2. Behavioral Evolution

Stanford University. The often asked question, what’s
the difference between Bio 150, Bio 250, and– is
it Hum Bio 160? No difference. It’s exactly the same. So like the same
requirements, same unit. So take whichever one
makes your life easiest. Let’s see. Any other procedural stuff? Well, the answers are back
from Monday’s questionnaire. And a variety of
interesting answers. Not surprisingly, given
the size of a group. Why have you taken this course? Really want to know about animal
behavior, but willing to deal with humans. [LAUGHTER] Because I’m substituting it Bio
43, which I don’t want to take. My dad used to make me read
books about human behavior and biology as punishment. [LAUGHTER] That doesn’t make any sense. I know one of the
TAs, so I figure that guarantees me an A. OK,
guys, that’s in your court. One I really liked,
because I want to be a filmmaker after college. Yay, interdisciplinary. What else? My first grade
teacher is making me. Tom McFadden told me to. I’m a hyper-oxygenated
dilettante. I wanted to, somewhat
correctly pointing out, why have you taken this class? I haven’t taken it yet. A number of people
reporting that, in fact, that was
the correct answer. And my favorite, why have
you taken this course? Yes. [LAUGHTER] OK. Relevant background,
relevant background. I’m human, I’m human
and I often behave. I’m human and I have biology. 19 years of being confused
about human behavior. Not really, sort of. Seeing crazy behavior as
an RA in an all frosh dorm. And I date a biologist. Let’s see. There was also the
question on there of, did the thing on the board
look more like an A or a B. And just to really
facilitate that one, I forgot to put
the A and the B up. But that taps into a
cognitive something or other, which maybe I’ll get
back to at some point. Telephone numbers. Reading them off,
accuracy dramatically tanked as soon as
the three number, four number motif
went down the tubes. And when it came back
briefly, accuracy came back a little bit. Finally, let’s see. All of you guys conform to
a standard frequent gender difference. Which is everybody was roughly
equally– by gender– roughly equally likely to see dependent
as the opposite of independent. A small minority went
for interdependent. However, one finding that
has come up over and over is that far more females are
interested in peace than males, males are more
interested in justice. OK, have you taken the bio core. Quote, no way Jose. Somebody pointing
out quite correctly, don’t settle for
peace or justice. Then of course,
there was the person who responded to that question
by writing those words are just symbols. Need to know assumed meaning. [LAUGHTER] OK. There was one questionnaire
that was carefully signed in something
approaching calligraphy, it was so beautiful. And was otherwise blank. For years running, the subject
that most people really want to hear, and most people
really don’t want to hear, is about the biology
of religiosity. And for 22 years running
now, Stanford students are more interested in
depression than sex. [LAUGHTER] OK. So we start off. I keep telling Hennessy about
this, but nothing gets done. We start off. We start off, if
I can open this– which is something
you can do if you have a certain type of training. If you’re some osteologist,
or whatever these folks are called. If you are presented
those two skulls and told this one’s
a female, this one’s a male, you can begin to figure
out stuff like how heavy, how large the body was
of that individual, what diseases they had, had they
undergone malnutrition, had they given birth, a
lot of times, a few times, were they bipedal. All sorts of stuff
you could figure out from just looking
at these skulls. What today’s lecture,
and Friday’s, is about is the fact that with the
right tools under your belt, you could look at
these two skulls and know that information. You are a field biologist, and
you’ve discovered this brand new species. And you see that this
one nurses an infant shortly before leaping
out of the tree, leaving only the skull. And this one has
a penis, shortly before leaping out of the
tree and leaving a skull. So all you know is this is an
adult female and an adult male. And if you’ve got the
right tools there, you can figure out who’s more
likely to cheat on the other. Is the female more likely to
mess around, or is the male? How high are the
levels of aggression? Does the female tend to have
twins, or one kid at a time? Do females choose males because
they have good parenting skills, or because
they’re big, hunky guys? What levels of differences
in life expectancy? Do they live the
same length of time? You would be able to tell
whether they have the same life expectancy or if there’s a big
discrepancy between the two. All sorts of stuff
like that, merely by applying a certain
piece of logic that dominates all of this. OK, so you’re back reading
those Time Life nature books back when, and there
was always a style of thing you would go through. Which is they’d
describe some species doing something absolutely
amazing and unlikely, and it goes like this. The giraffe, the
giraffe has a long neck, and it obviously has
to have a big heart to pump all that blood up there. And you lock up a whole
bunch of biomechanics people with slide rules, and out they
come out with this prediction as to how big the
giraffe heart should be and how thick the walls. And you go and you
measure a giraffe heart, and it’s exactly what
the equations predicted. And you say, isn’t
nature amazing? Or you read about some desert
rodents that drink once every three months, and
another bunch of folks have done math and figured
out how many miles long the renal tubules have to be. And somebody goes
and studies it, and it’s exactly
as you expect it. Isn’t nature wonderful? No, nature isn’t wonderful. You couldn’t have
giraffes unless they had hearts that were that big. You couldn’t have rodents
living in the desert unless they had kidneys that
worked in a certain way. There is an inevitable logic
about how organisms function, how organisms are
built, how organisms have evolved solving this
problem of optimizing the solution. And what the next two
lectures are about is, you can take the
same exact principles and apply them to thinking
about the evolution of behavior. The same sort of
logic where, just as you could sit there and,
with logical principles, come to the point of
saying, a giraffe’s heart is going to be this big. You can go through a
different realm of logic built around evolutionary principles
and figure out all sorts of aspects of social behavior. And we already know what’s
involved in, say, optimizing. What’s the optimal number
of whatevers in your kidney. What’s the optimal behavior
strategy or something. All of us, as soon as
we got some kid sibling, learned how to do the optimal
strategy in tic-tac-toe. So that you could never lose,
and it’s totally boring. But that’s a case of figuring
out the optimal solution to behavior, reaching what is
called the Nash equilibrium. And actually, I have no
idea what I just said. But I like making
reference to Nash, because it makes me feel
quantitative or something. So that is called
the Nash equilibrium. The Nash equilibrium, and
what the entire point here is, the same sort of
process of figuring out what are the rules of
optimizing tic-tac-toe behavior can be built upon the
principles of evolution to figure out all
sorts of realms of optimized social behavior. And broadly, this is a field
that’s known as sociobiology, emerging in the late
1970s– mid 1970s or so. And by the late
1980s, giving birth to another discipline known
as evolutionary psychology. The notion that you cannot
understand behavior, and you cannot understand
internal psychological states, outside the context of evolution
had something to do with sculpting those behaviors
and those psyches. So to start off with that, basic
song and dance about Darwin. Just to make sure we’re
up to speed on this. Darwin, just to get some
things out of the way. Darwin did not
discover evolution. People knew about
evolution long before that. Darwin came up with the
notion of a mechanism for evolution,
natural selection. And in fact, Darwin is
the inventor of that. There was another guy,
Alfred Russel Wallace, the two of them. And, for some reason, Wallace
has gotten screwed historically and Darwin gets
much more attention. But starting off with a
Darwinian view of how evolution works. First thing being that
there is evolution. Traits in populations
change over time. Traits can change enough
that, in fact, you will get speciation. New species will form. And the logic of
Darwinian evolution is built on just a few couple
of very reasonable steps. First one is that there are
traits that are heritable. Traits that could be passed
on one generation to the next. Traits that we
now can translate, in our modern parlance, into
traits that are genetic. And we will see, soon, how
that’s totally not correct to have said that. But traits that are heritable. The next thing is that there is
variability among those traits. There’s different ways in
which this trait can occur, and they’re all heritable. The next critical thing. Some versions of those traits
are more adaptive than others. Some versions work
better for you. For example, giraffe
who wind up with hearts the size of, like, a tomato,
that’s not an optimal version. Amid the range of
variability, some will carry with them more
fitness, more adaptiveness, than others. And that translates
into another sound bite that’s got to be gotten rid of. All of this is not about
survival of the most adapted. It’s about reproduction,
something we will come to over and over again. It’s about the number
of copies of genes you leave in the next generation. So you’ve got to have
traits that are heritable. There’s got to be
variability in them. Some of those traits are
more adaptive than others. Some of those
traits make it more likely that that organism
passes on copies of its genes into the next generation. And throw those three pieces
together, and what you will get is evolution in populations. Changing frequencies of traits. And when you throw in one
additional piece, which is every now and
then the possibility to have a random introduction
of a new type of trait in there– modern parlance,
a mutation– from that, you can begin to get actual
large changes in what a population looks like. OK, so these are the basic
building blocks of Darwin. And it is easy to apply
it to giraffes’ hearts and kidneys of desert rats,
and everything we think about in the world of
physiology, anatomy, in the context of evolution. So how do you apply
it to behavior? And the basic notion,
for folks who’ve come from this
Darwinian tradition into thinking about behavior,
is you do the exact same thing. There are behaviors that are
heritable, types, traits, classes of behaviors. They come with a certain degree
of variation among individuals. Some versions of them are
more adaptive than others. Over time, the more
adaptive versions will become more commonplace. And every now and then,
you can have mutations that introduce new variability. Totally logical,
absolutely unassailable. And what we’re going to spend
an insane amount of time in this class on is
one simple assumption in there, which is that certain
behaviors are heritable. That certain behaviors
have genetic components. And as you’ll see,
this one is just going to run through
every lecture wrestling with that issue there. This is a big incendiary issue
there as to how genetic– and that’s not the
same thing as saying how genetically determined–
how genetic behavior is. So that’s going to be an
issue we come back to again and again. So now, transitioning
into how you would apply these Darwinian principles. First thing before
starting, a caveat. You’re going to wind up,
in order to think about all of this most efficiently,
hopefully do some personifying. Personifying as in, you’ll
sit around saying, well, what would a female
chimpanzee want to do at this point to
optimize the number of copies of her genes in the
next generation? What would this
brine shrimp want to do to deal with this
environmental stressor? What would this cherry tree do? They’re not planning. They’re not conscious. They’re not taking classes
in evolutionary biology. What would this
organism want to do is just a shorthand
for something sculpted by the sort of
exigencies of evolution, and reducing the optimal. They want to do this. This is just going to be
a short hand throughout. Once you get past
the apes, nobody is wanting to do any of
these optimization things. So just getting that sort of
terminology out of the way. OK, so we start off with
what’s the first building block of applying Darwinian
principles to behavior. Something that is absolutely
critical to emphasize, because the first
thing we all need to do is unlearn something we all
learned back when on all those National Geographic specials
and that would consistently teach us something about
this aspect of evolution, and would always
teach it to us wrong. Here’s the scenario. So you’re watching, and there’s
this wildlife documentary. It’s dawn on the savanna. And you see, there’s
a whole bunch lions on top of some big
old dead thing. Some buffalo, or something. And they’re chewing away
and having a fine time. So something happens
at that point, which is, they have to deal
with how they divvy up the food. Or let me give you
another example. Another standard, sort
of endless vignette that comes up in these films. Once again, now, you’re
back on the savanna. It’s not dawn this
time, but you are looking at one of the
magnificent things of the natural world, which
is the migration of zebras throughout East Africa. A herd of 2 million of them
migrate around, following a cyclical pattern of rains. So they’re always going
where the grass is greener. So you’ve got this wonderful
herd of 2 million wildebeest, and there’s a problem. Which is, there’s some great
field right in front of them full of grass, and
bummer, there’s a river in between them
and the next field. And especially a bummer, a
river teeming with crocodiles just ready to grab them. So what are the
wildebeest going to do? And according to the
National Geographic type specials we would get,
out would come a solution. There’s all the wildebeest
hemming and hawing in this agitated state
by the edge of the river. And suddenly, from
the back of the crowd, comes this elderly wildebeest
who pushes his way up to the front, stands on
the edge of the river and says, I sacrifice
myself for you, meine kinder, and throws
himself into the river– [LAUGHTER] –where immediately, the
crocs get busy eating him up. And the other two
million wildebeest could tiptoe around the
other way across the river, and everybody is fine. And you’re then saying,
why’d this guy do this? Why did this guy fling
himself into the river? And we would get the
answer at that point. The answer that is permeated
as, like, the worst urban myth of evolution. Whatever. Why did he do that? Because animals behave for
the good of the species. This is the notion that has
to be completely trashed right now. Animals behaving for
the good of the species really came to the forefront,
a guy in the early 60s named Wynne-Edwards. Hyphenated, Wynne-Edwards. Some hyphenated Brit zoologist,
who pushed most strongly this notion of
that animals behave for the good of the species. He is reviled throughout
every textbook, Wynne-Edwards and group selection. That would be the
term, selection for the good of groups,
for the selection for the good of the species. Wynne-Edwards and
group selection. I’m sure the guy did all
sorts of other useful things. And anyone who really has any
depth to them would find out. But all I know is that
the guy is the one who came up with group selection. Animals behave for the
good of the species. This isn’t the case at all. Animals behave for passing on
as many copies of their genes as possible. And what we’ll see
is, when you start looking at the nuances
of that, sometimes it may look like behaving for
the good of the species. But it really isn’t the case. So animals behave
in order to maximize the number of
copies of genes they leave in the next generation. Remember, not survival
of the fittest, reproduction of the fittest. So first thing you need to do
is go back to that vignette and saying, so what’s up
with the wildebeest there? And what’s up with the elderly
guy who jumps in the river? And finally, when you
look at them long enough instead of the camera crew
showing up for three minutes, when you studied
this closely enough, you see something that
wasn’t apparent at first. Which is, this
elderly wildebeest is not fighting his
way through the crowd. This guy is being
pushed from behind. [LAUGHTER] This guy is being
pushed from behind, because all the other
ones are saying, yeah, get the old
guy on the river. Sacrificing himself, my ass. This guy is getting pushed
in by everybody else. He is not sacrificing himself
for the good of the species. He does not like the
idea of this whatsoever. So he gets pushed in
because the old, weak guy. None of this group
selection stuff. What came in by the
’70s as a replacement, a way to think about this,
is this notion of animals, including us, behaving not
for the good of the species or of the group, but to maximize
the number of copies of genes left in the next generation. And what you see is three ways
in which this could occur. Three building blocks. The first one being known
as individual selection. The first one, built
around the notion that sometimes the
behavior of an animal is meant to optimize the
number of copies of its genes that it leaves in
the next generation by itself reproducing. The drive to
reproduce, the drive to leave more copies
of one’s genes. This was once summarized
really sort of tersely as, sometimes a chicken is an egg’s
way of making another chicken. No, that’s backwards. Sometimes a chicken is an egg’s
way of making another egg. OK, ignore that. What the guy said is, sometimes
a chicken is an egg’s way of making another egg. All this behavior stuff,
and all this animate social interaction, is just
an epiphenomenon to get more copies of the
genes into the next generation. Individual selection, a subset
of way of thinking about this is selfish genes. What behavior is
about is maximizing the number of copies of
genes in the next generation. And sometimes the best
way to do it, sometimes the way that animals maximize,
is to get as many copies by way of reproducing
themselves. It’s not quite equivalent
to The Selfish Gene, but for our purposes,
individual selection. And this can play out
in a number of realms. And bringing in sort
of a big dichotomy in thinking about
evolutionary pressures, Darwin and the theory of
natural selection. What natural
selection is about is processes bringing about an
organism who is more adaptive, what we just went through. Darwin soon recognized there
was a second realm of selection, which he called
sexual selection. And what that one’s
about is, this is selecting for
traits that have no value whatsoever in terms of
survival or anything like that. Traits that carry
no adaptive value, but for some random, bizarre
reason, the opposite sex likes folks who look this way. So they get to leave more
copies of their genes. And suddenly, you could have
natural selection bringing about big, sharp
antlers in male moose, and they use that for fighting
off predators or fighting with a male. That would be natural selection. Sexual selection might
account for the fact that the antlers are
green, paisley patterns all over for that. And for some reason,
that looks cool. The female moose is,
and what you wind up getting as a mechanism
for sexual selection is, as long as individuals
prefer to mate with individuals with some completely
arbitrary traits, those traits will also
become more common. So this dichotomy
of natural selection for traits driven by
traits that really do aid leaving copies of genes
outside the realm of just sheer sexual preference,
sexual selection. And sometimes they can go in
absolutely opposite directions. You can get some species
where the female fish prefer male fish that have
very bright coloration. And that’s advantageous, then,
to have the bright coloration by means of sexual selection. But the bright
coloration makes you more likely to get predated
by some other fish. Natural selection pushing
against bright coloration in males. Very often, you’ve got the
two going against each other, having to balance. So how would that be
applied in this realm of individual selection? This first building block. Sometimes an egg– damn. Sometimes a chicken is an egg’s
way of making another egg. Sometimes what behavior is
about is one individual trying to maximize the number
of copies of their genes in the next generation. A natural selection
manifestation of it being, you’re good at
running away from predators. Selection for speed, for certain
types of muscle metabolism, for certain sets of sensory
systems that will tell you there’s somebody scary around. That would be the realm of that. Individual selection, selecting
the realm of sexual selection to have more of whatever those
traits that are attractive. So this first building block,
it’s not group selection. It’s not behaving for
the good of the species. It’s behaving to maximize the
number of copies of one’s genes in the next generation. And the most
straightforward way is to behave in a way to
maximize the number of times you reproduce yourself. Second building
block, which is, there is another way of accomplishing
the same thing that you just did with individual
selection, as follows. One of the things that
can be relied upon in life is that you are related
to your relatives. And what you get is, the
more closely related you are, the more genes you share
in common with them. On a statistical
level, identical twins share 100% of their genes. Full siblings, 50%. Half siblings, 25%. This is exactly
something that’s going to be covered in the catch
up section this week. If you’re not comfortable with
this stuff, this sort of thing will be reviewed in more detail. OK, so the closer a
relative is to you, the more genes they
share in common with you. So suddenly, you’ve
got this issue. You’re an identical twin
and your identical sibling has the same genes that you do. Individual selection, you
will be just as successful as passing on copies of your
genes into the next generation if you forgo
reproducing to make it possible for your
identical twin to do so. Because on the level
of just sheer numbers of copies of genes in
the next generation, they are equivalent. And sometimes, you will thus get
behavior which really decreases the reproductive
success of an individual in order to enhance the
success of a relative. But you’ve got a
constraint there, which is, all of
your relatives don’t share all your genes with you. They have differing
degrees of relatedness. And what that winds up
producing is another factor, another observation. One of the great, witty
geneticists of all time, a guy named Haldane who,
apparently, once in a bar was trying to explain
this principle to somebody and came up and
said, I will gladly lay down my life for two
brothers or eight cousins. And that’s the math
of the relatedness. You passing on one
copy of your genes to the next generation is, from
the sheer mathematics of just how evolution is going to
play out over the generations, is exactly equivalent as giving
up your life for eight cousins to be able to each pass
on a copy of their genes. Because you share 1/8
with each of them, and it winds up being
a whole [INAUDIBLE]. And it’s that math. And out of that, you
get something that makes perfect sense instantly. Which is, evolution selects
for organisms cooperating with their relatives. Something along those lines. And thus we have this
second building block known as kin selection. Inclusive fitness. Kin selection. First building block, individual
selection, passing on copies of your own genes as a way
to maximize future success. Second version,
helping out relatives. Helping out relatives
in terms of increasing their reproductive success
with this vicious mathematical logic, which is
one identical twin to have two full siblings,
eight cousins, and so on, as a function of
degree of relatedness. And what this begins to
explain is a whole world in animal behavior of animals
being obsessed with kinship. Animals being fully aware of
who is related to who in what sorts of ways. Animals being
utterly aware of you cooperate with relatives,
but as a function of how closely related they are. Animals put us in Social
Anthropology, in kinship terms, and could you marry the daughter
of your uncle’s third wife or whatever, to
shame in terms of how much a lot of social animals
deal with relatedness. So inclusive fitness,
kin selection. Here would be evidence for it. Here’s one example. Very cool study done some years
back by a couple, Seyfarth and Cheney, University
of Pennsylvania, looking at vervet monkeys. And these were vervet monkeys
out in Tanzania, I believe. What they did was, a whole
bunch of these vervet monkeys were sitting around. And they, the researchers,
had made really high quality recording recordings of
various vocalizations from the monkeys over time. So they had the sound of each
animal giving an alarm call, giving a friendly gesture
call, giving a whatever. And what they would then
do is hide a microphone inside some bushes and play
the sound of one of the infants from the group
giving an alarm call. So what does the mother
of that infant do? She instantly gets agitated
and looks over at the bush. That’s her child, all of that. How to know that everyone
else in that vervet group understands kin selection,
what does everybody else do? They all look at the mother. That’s whoever’s mother,
what is she going to do next? They understand the
relatedness, and they understand what the response will be. All the other vervets look
at the mother at that point. Whoa, I’m sure glad that’s
not my kid giving an alarm call from the bushes. They understand kinship. Another version of that
came out in these studies. So you’ve got two females, each
of whom has a kid, a daughter, whatever. And female A and female
B. And one day, female A does something absolutely
rotten to female B. And later that day,
the child of female B is more likely than chance
to do something rotten to the child of
female A. They’re keeping track of
not only revenge, but not revenge on
the individual who did something miserable to
you, but displaced by one degree of reproduction. Keeping track of kinship. Animals can do this. All sorts of primate
species can do this. And as we’ll see, all sorts of
other species can do this also. There is that caveat again. All sorts of other
species want to figure out who their cousins– they
don’t want to figure out. Evolution has
sculpted an ability to optimize behavior
along lines of relatedness in all sorts of species. So how would natural
selection play out in this realm of kin
selection, I will lay down my life for eight cousins. And that’s just sort of
obvious there by now. How would sexual selection
play out in this realm. I am willing to expend
great amounts of energy to convince people that my
sibling is incredibly hot. And with any
chance, then passing on more copies of genes. That would be inclusive fitness,
kin selection in both cases. Decreasing your own
reproductive potential by way of being killed by a
predator to save the 8 cousins, or having to spend so much time
haranguing about your sibling. Doings that, in
order to increase the reproductive
success of relatives, where you were willing
to give up more energy and potential on your part,
the more closely related the individual is. So you throw those
two pieces together, and you’re suddenly
off and running with explaining a lot
of animal behavior. Individual selection,
none of this for the good of the species. Maximizing the number of
copies of your own genes. And the easiest way, the
most straightforward, is you yourself
maximizing reproduction. Foundation number two the
whole thing, kin selection. Sometimes the best way of
leaving more copies of genes in the next
generation is using up your own reproductive
potential foregoing to help relatives as a function
of degree of relatedness. OK, that’s great. So now the third piece, the
third final building block of making sense of social
behavior in the context of real contemporary
evolutionary theory, the third block here. Which is, you look at animals
and they’re not all just competing with non-relatives. Animals forego competition
at certain points. Animals would have
the potential to be aggressive to other animals,
and they will forego doing so. And there’s one circumstance
in which that can happen, where you get what is called a
rock-paper-scissors scenario. You’ve got animals A, B, and
C. A has a means of damaging B, but it costs A. B has
a means of damaging C, but it costs B. C
can damage A, but it costs A. You get the right
distribution of individuals with one of those
traits in a population, and you will reach a
rock-scissors-paper equilibrium where nobody’s doing anything
rotten to each other. Great example, totally
cool example that got published some years ago by a
guy named Brendan Bohannan, who was assistant professor in the
department here at the time. He was studying something
or other about bacteria showing a rock-paper-scissors
circumstance. You had three different types,
three different versions, of this bacteria in
this colony he had made. The first one could generate
a poison, but it cost. It had to put the effort
into making that poison and protecting itself from
that poison, all of that. The second type was
vulnerable to the poison. It happened to have some
transporter on its membrane that took up the poison,
and that was bad news. But it had an advantage,
which is the rest of the time, that transporter
took up more food. The third one, the
good thing going for it is that it didn’t
have– the bad thing was, it didn’t have poison. A good thing going
for it was it didn’t have to spend
energy on a poison, and it didn’t have
that transporter. So each one of those has a
strength, each one of those has a vulnerability. They’re like, I don’t
know, Pokemon or something. And you put them
all together there, and you get a
rock-paper-scissors scenario where you get equilibrium,
where they are not attacking each other. Because note, if I
am A and I destroy B, B’s no longer
wiping out C, who’s the one who could damage me. It’s got to come to
an equilibrium state. So you can get the evolution
of stalemates like that, and that’s quite
frequently seen. And note here, this
was the evolution of stalemates not in chimps, not
in cetaceans, but in bacteria. What we’re going to see
is bacterial behavior, to the extent that this is sort
of a metaphor for behavior. Behavior of all sorts
of unlikely species are subject to these
same rules of passing on copies of your genes. These three different
strains of bacteria are competing with each other. None of them are behaving for
the good of the species there of the three of them. So rock-paper-scissors
is very cool, and you get versions
of that in humans. That’s been sort of studied
quantitatively, all of that. But that’s not real cooperation. That’s merely
everybody realizing we have to cut back
on the competition. We have to cut back
on the aggression. Because every time
I damage whoever, I am more vulnerable
in another realm. That’s a stalemate. That’s a truce. But you look at animals,
and in all sorts of realms, it’s not just
rock-paper-scissors stalemates they’re reaching. They actually cooperate
with each other. And you look close enough, and
you see they’re not relatives. They’re not
relatives, yet you get all sorts of
altruistic behavior, and you’ve got it under
a whole bunch of domains. Because this brings
up the question, why should you
ever be cooperative with another individual if
you are a social animal. At every possibility, you
should stab them in the back and be selfish. And the reason why
that isn’t a good idea is, there’s all sorts
of circumstances where many hands make the task light. Or whatever that is, cooperation
can have synergistic benefits. And you see that
with species that are cooperative hunters,
where they are not necessarily relatives. They will chase one,
chasing an animal while the other is getting
ready to cut a corner on it. Cooperative behavior, and
they increase the likelihood of them getting a kill. Another example of this. Research by a guy
named Mark Hauser at Harvard looking
at rhesus monkeys. And what he showed was,
he would put these monkeys in a situation where
they had access to food. They had access to food
under one circumstance, where they could reach for it
and take it in and share it with another monkey. Under the other circumstance,
it required two monkeys to get the food in there. And what he showed was
clear cut reciprocity. Monkeys who were
sharing with this guy were more likely to
get shared back with and got more cooperation when
it was a task where two of them had to work together
to get the food. One alone wasn’t enough. Many hands make the task
lighter under all sorts of circumstances. Cooperation has a strong
evolutionary payoff, even among non-relatives,
with a condition. Which is, you’re not
putting more into it than you are getting. That is reciprocal. And ‘ opens up the third
building block of all of this, which is reciprocal altruism. Cooperation, altruistic
behavior among non-relatives, but undergoing very
strict constraints of, it’s gotta be reciprocated with
all sorts of rules like that. So what does that look like. You’re going to see
reciprocal altruism, when would you see that. What’s the immediate
thing, what sort of species would show systems of
reciprocal cooperation among non-relatives. They’ve got to be smart animals. They’ve got to be social. They’ve got to be smart. Why do they have to be smart? Because they have
to remember, this is the guy who owes me a
favor from last Thursday. They need to be able to
recognize individuals. They have to be long lived
enough so that there’s a chance of interacting
with that individual again and establishing
this reciprocity. You would thus
predict you would see systems of reciprocal
altruism only in long lived social vertebrates. But you see the exact sorts
of things in bacteria. You see the exact sort
of things in fungi. You see that in all
sorts of other realms. You get social bacteria,
colonizing bacteria. And where what you might
get are two clonal lines that are together. In other words, two
genetically– two lines, each of which is,
all the bacteria have the same genetic makeup. So think of it as one individual
who’s just kind of dispersed. Another one who’s just
kind of dispersed. And they’ve come
together in something called a fruiting body, which
is how bacteria reproduce or whatever. And there’s two parts
to a fruiting body. There’s one which
is the stalk, which attaches to something or other. And then there is the
part that actually fruits. So you want to be in
the fruiting part, because that’s the part
that actually reproduces, and the stalk is doing
all the work there. And what you see is
attempts at cheating. Attempts at one of
these strains trying to disproportionately wind
up in the fruiting part, and what you also
see is, the next time around, this other strain
will not cooperate with it. Will not form a social colony. So that’s getting played off
at the level of single cell organisms forming
big social colonies. Getting played at that level. Yes, as we will see,
reciprocal altruism works most readily
in big, smart, long lived social beasts. But it can occur in
all sorts of systems. What it’s built around is
reciprocal cooperation. And intrinsic in that it
is another motivation going on there. Not just to involve the
reciprocal relationship with a non-relative, and
many hands, and light tasks, and all of that. But also, whenever
possible, to cheat. To take advantage of
the other individual. And thus, another
key facet of it is to be very good at
detecting when somebody is cheating against you. To be vigilant about
cheating in what would otherwise be a stable,
reciprocal relationship. And an awful lot
of social behavior is built around
animals either trying to get away with something
or spotting somebody else doing the same. An example of it. There is a test that’s used
in evolutionary psychology where you are given this
very complicated story, or another version of a
complicated story, where somebody promises if you do
this, you’ll get this reward. But if you do that, you’re
going to get this punishment. And really complex. And one outcome,
the outcome of it is, the person isn’t
supposed to get rewarded. But the individual
decides to reward them. Spontaneous act of kindness. In another
circumstance, the person is the individual who is
supposed to get rewarded, and instead, they get punished. A cheater in that case. And amid these
convoluted stories, people are much
better– 75% to 25%– are much better at detecting
when cheating has gone on in the story than when a
random act of kindness has gone on. We are more attuned to
picking up cheating. And remarkably, some
very subtle studies have been done
with chimps showing that chimps have the same bias. They are much
better at picking up social interactions involving
cheating than ones that involve spontaneous altruism. So you see here, this
balance between cooperation, reciprocal, even
among non-relatives. And that’s great,
but you should cheat when you can get away with it. But you should be
vigilant against cheaters. And what, of course,
it comes down to then is tic-tac-toe and giraffe
hearts and all of that. What is the optimal strategy
in a particular social species for a particular individual. What is the optimal strategy. When do you cooperate
and when do you cheat. When do you defect on the
cooperative relationship you’ve had. And this introduces
us to a whole world of mathematics built around
what is called game theory. The notion that there are
games, formal games, that have mathematically
optimal strategies, or multiple strategies,
multi-equilibrium. And a whole world
of research has been built around them in
terms of when to cooperate and when to defect. So game theory stuff. This was starting off
in a world of people studying economics, and
negotiation, and diplomacy, and all of that. And that was a whole world
built around this logic of when do you cooperate,
when do you cheat. And what came out of
there were all sorts of models of how to optimize
behavior in terms of that. And the building block, sort of
the fruit fly of game theory, is a game called the
prisoner’s dilemma. Prisoner’s dilemma, sort of
cutting to– sort of getting rid of the details. Two individuals are
prisoners, and they escape, and they’re both captured. And they’re
interrogated separately. And both of them refuse to
talk, that’s great for them. If they both squeal,
they both get punished. If one of them is able to
squeal on the other one, they get a great reward. If the other one–
what you get formally are four possible outcomes. Both individuals
cooperate, both individuals cheat against each other,
individual A cooperates and B cheats, individual B
cooperates and A cheats. And what you get in
prisoner’s dilemma is a formal payoff for each. What gives you the
greatest payoff, stabbing the other guy in the back. You cheat and they cooperate. You have exploited them, you
have taken advantage of them, isn’t that wonderful. That’s the highest payoff
in prisoner dilemma games. Second highest payoff,
you both cooperate. Third highest payoff–
which is beginning to not count as a payoff, but in
a lot of the games, this set up is the start of
punishment– both of you cheat on each other. Fourth worst possible
payoff is you’re the sucker. You cooperate, and
the other individual stabs you in the back. So what the prisoner’s
dilemma game is set up these circumstances
where individuals will play versions of this against each
other with varying rewards and that sort of thing,
and parameters that we will look at in a lot of detail. And seeing when is it
optimal to cooperate, when is it optimal to cheat. When would you do this. So you’ve got examples
of this, and this was the building block. And what anyone would
say looking at this is, it’s obvious. What you want to
do is, in some way, rationally maximize your payoff. This whole world
of Homo economists, the notion of humans as being
purely rational decision makers. And what you begin to see in
this world of game theory is, there is anything
but that going on. Later in the course,
we’re going to see something very interesting. People playing prisoner’s
dilemma games inside a brain scanner, looking at a
part of the brain that has a lot to do with pleasure. And what you see
is, some individuals activate that part of the brain
when they have successfully stabbed the other
guy in the back. Some individuals activate it
when they have both cooperated. And there’s a big
gender difference as to which circumstance. [LAUGHTER] So you just guess which
one is going on there. We’re going to see
a number of studies like that coming down the line. So the question
becomes, how do you optimize prisoner dilemma play? And what emerged
at that time was the notion of all sorts of
theoretical models and stuff. And then in the 1970s,
there was an economist at University of Michigan
named Robert Axelrod who revolutionized the entire field. What he did was he took
some paleolithic computer and programmed in how the
prisoner’s dilemma would be played. And he could program in as
if there were two players. And he could program in what
each one’s strategy would be. And what he then did was, he
wrote to all of his buddies and all of his mathematician
friends and prize fighters and theologians and serial
murderers and Nobel Peace Prize winners, and in
each case, explained what was up and saying,
what strategy would you use in a prisoner’s dilemma game? And he gets them all
back, and he programs all these different versions. And he runs a round
robin tournament. Every strategy is paired
against every other strategy at one point or other. And you look at
what the payoff is. You ask, which is the
most optimal strategy. And out of it,
shockingly to everyone– because this was a computer
teaching us optimizing human behavior– out of it
came one simple strategy that always out-competed the others. This is people sitting
there, probabilistic ones as to when to cooperate, and
lunar cycles as to what to do. The one that always won
is now called tit for tat. You start off cooperating
in the very first round with the individual. You cooperate. If the individual has cooperated
with you in that round, you cooperate in the next round. And you cooperate,
cooperate, as long as the other
individual cooperates. But as soon as there is a round
where the individual cheats against you, you cheat
against them the next time. If they cheated at
you that time also, you cheat against
them the next time. If they go back to
cooperating, you go back to cooperating
the next time. You have this tit
for tat strategy. In the absence of somebody
stabbing you in the back, you will always cooperate. And what they found
was, run these hundreds of thousands of versions of
these round robin tournaments, and tit for tat was the
one that was most optimal, to begin to use a
word that is not just going to be a metaphor. Tit for tat always drove
the other strategies into extinction. And what you wound up seeing
is this optimized strategy. And it was very clear why
tit for tat worked so well. Number one, it was nice. You start off cooperating. Number two, it retaliates if
you do something crummy to it. Number three, it is forgiving. If you go back to cooperating. Number four, it’s
clear cut in its play. It’s not some
probabilistic thing. What you get, then,
with tit for tat is, suppose you’re playing three
rounds with another individual. You both cooperate
the first one, you both cooperate the next one. You’re playing tit
for tat strategy, so you cooperate on this one. And they stab you in the back,
and you can’t get back at them, because this is the last round. What you’ll see is, under
lots of circumstances, tit for tat is disadvantageous. But what the soundbite is
about it is, tit for tat may lose the battles,
but it wins all the wars. This pattern of being nice,
but being retaliatory, being forgiving, and being
clear in the rules, drives all the other
strategies into extinction. OK, at this point my
alarm just went off, which was to remind
me to ask somebody who is wearing a life vest– is
somebody wearing a life vest? [INAUDIBLE] Over there. Where are you? She just left. She left. Isn’t that interesting? Somebody put me up to
having to ask this person, why are you wearing a life vest? And apparently the
answer she would give was going to free all sorts of
captives in some rebel group in Colombia. And she fled. OK, what that does is– [LAUGHTER] I don’t know what that says
about reciprocal altruism. But what that says also
is, after I do a summary, don’t make a move. We will have a
five minute break. So what do we have
at this point, we have the first building
block of optimizing the evolution of behavior,
like optimizing giraffe hearts. First piece, you don’t behave
for the good of the species. Individual selection,
passing on as many copies of your own genes as possible. Sometimes a chicken is an egg’s
way of making another egg, he says triumphantly. Building block number
two, kin selection. Some of the time, the best way
to pass on copies of your genes is by way of helping relatives. Kin selection, with the
mathematical fierceness of degree of
relatedness driving it. Piece three, sometimes
what’s most advantageous is to cooperate, even
with non-relatives, but with the rules of
it has to be reciprocal and you have to
cheat when possible. You have to be on
guard against cheaters. And as we’ve just seen, game
theory, prisoner’s dilemma, beginning to formalize
optimal strategies for that. OK, let’s take a
five minute break. But promise you will
come back if you go out, and everyone won’t wander off. Altruism [INAUDIBLE] game
theory as being a form or way to maximize that behavior
in a very artificial realm, but stay tuned. Prisoner’s dilemma
as the building block of how to do this amid
lots of other types of games that are used. But prisoner’s dilemma
is the most basic one. And that round robin tournament,
that computer simulation, Axelrod asking all his
buddies to tell him what strategy would you use,
run them against each other, and out comes tit for tat. Tit for tat drives all the
others into extinction. However, there is
a vulnerability in tit for tat,
which is– OK, so. We have the technical way of
showing prisoner’s dilemma play. And first round, both
individuals are cooperating. Second round, both
individuals are cooperating. Third round, this one
cheats– those are fangs. This one cheats and
this one cooperates. So the next round, this
one now cheats and this one goes back to cooperating,
and we’ve just gotten through a scary thing
that tit for tat solves, and it’s great. Wonderful. What if, though, your
system is not 100% perfect. What if there’s
a the possibility of a mistake being made, of
sending the wrong signal. What if there’s the possibility
of noise in the communication system. And at some point,
an individual who does a cooperative
behavior, thanks to a glitch in the system, it is read
as having been defection. So what happens as a result? This individual– forget it. OK, what happens as a result.
The individual who cooperated, but somehow the message
got through as cheating, they don’t know. Something got lost in the wires
between them in translation. The other individual
was saying whoa, that individual
cheated against me. I’m going to cheat
in the next round. So along comes the next
round, and that individual cheats against them. This one who’s cooperating,
because they’ve been cooperating all along. They don’t know
about this error. And they say whoa, that person
just cheated against me. I’m going to cheat
in the next round. So they cheat in the next round. This one says whoa, they
just cheated another time, again and again and again. And what you get is a seesaw
pattern for the rest of time. You’ve just wiped out
50% of the cooperation. And what you’ve got is
tit for tat strategies are vulnerable to signal error. That’s something that soon
came out in these studies of Axelrod’s. When I was a kid, there was
like one of these thriller books I remember reading where
there’s a glitch in the system. And at the time, the
mean scary Soviet Union launched a missile that–
no, it was the United States. The United States,
by accident, launched a missile, a nuclear weapon,
where they didn’t mean to. Some cockroach chewed through
a wire some place or other. And the missile went off, and
wound up destroying Moscow. And oh my god, we had
a cooperative system of mutually restraint of
aggression, all of that. And thanks to a signal
error, a cheating signal was accidentally sent off. And how did the book end? A tit for tat response. In order to avoid
thermonuclear wasteland, the Soviet Union was
allowed to destroy New York. All right, so that
shows exactly how you could then get into
a see-sawing thing, simply by way of if the
system has any vulnerability to signal error. So it soon became clear,
as soon as Axelrod began to introduce the
possibility of signal errors, that tit for tat didn’t work as
well as another strategy, one that quickly came
to the forefront. And that one– for
some strange reason, that’s the way it’s shown. That one was called
forgiving tit for tat. What happens with
forgiving tit for tat? The usual rule, like tit
for tat, if you cooperate, if they cooperate,
you always cooperate. If they cheat against you, you
punish them in the next round. Exactly the same
thing as tit for tat, but oh no, what if there’s
a signal error in the system and you’ve gotten caught in
one of these horrible seesawing things. What forgiving tit
for tat does is, we’ll have a rule, for
example, that if we see saw like this
five times in a row, I will forego cheating
the next time. And instead, I’ll cooperate. And that will get
things back on track. I am willing to be
forgiving in one round in order to
re-establish cooperation after the signal error came in. And that one– as
soon as you introduce the possibility of signal
error, that one out-competes tit for tat. Because it makes perfect sense. It’s a great way of
solving that problem. So that was terrific. Tit for tat with the
ability to forgive, and what you would then see is
variability, how many of these do you need to go through
before you forgive, what’s the optimal number
of see-sawings, all of that. So a whole world of optimizing
how soon you’re forgiving. Nonetheless, the general
theme being forgiving tit for tat out-competes tit for tat
when you can have signal error. But there is a vulnerability. There is a vulnerability
here to this one, which is, you could be exploited. If you’re playing against,
for example, a tit for tatter, or all sorts of other
strategies, where they don’t have forgiving
strings of defection and you do, what’s
going to happen is you’re going to keep
going back to cooperating, they’re going to keep
stabbing you in your back. Forgiving tit for tat is
vulnerable to exploitation playing against
individual players that don’t have forgiveness in them. So what soon became apparent was
an even better strategy, which is you start off with
a tit for tat strategy. Which is, you are
punitive, you are retaliatory amid being
forgiving, clear and nice initially. You are willing to punish, and
you cannot be exploited in this way. If and only if you have gone
whatever number of rounds without the other individual
ever cheating on you, if you’ve gone long enough
without that happening, you switch over to
forgiving tit for tat. What is that? That’s deciding
you trust somebody. You’ve had enough
interactions with them that you are willing
to trust them. This is the transition from
pure rational optimizing to switching over, forgiveness
coming in there protects you from signal error. And of course, now, a whole
world of how many rounds do you need to do this before
you switch that as to what the optimal deal with that is. But again, this is a
way of transitioning to solve the problem
of signal error, but forgiving too readily
and being taken advantage of. Soon, another strategy appeared,
which was called Pavlov. And those of you who
know Pavlovian psychology will see that this, in fact,
has nothing whatsoever to do with Pavlovian psychology, and
I don’t know why they did that. But they thought it
was kind of cool. But the rule was
remember, if you stab the other guy in the back,
you get a bunch of points. If you both cooperate, you
get points, not as many. If you both cheat,
you lose some points. If you’re taken advantage
of, you lose a lot of points. So two outcomes you gain,
two outcomes you lose. In Pavlov, the simple rule
is when I do something, if I get points, if I get
some degree of reward, I do it again the next time. If I get rewarded in either of
the first two types of payoffs, I do the same thing again. And the other part, of course,
is, if I play my strategy and I lose one of the
two bottom outcomes, I switch to the other
strategy the next time. And what you see is that
can establish very good tit for tat stuff. But if you sit and
spend hours tonight with a long roll of
toilet paper and playing out all the rounds
of it, you will see what Pavlov allows
you to do is exploit somebody else who is forgiving. So Pavlov goes along
just fine with this. And as long as Pavlov continues,
whenever they switch over to a forgiving tit
for tat, Pavlov will out-compete them,
because Pavlov exploits. What then emerged was just
zillions of people studying all sorts of games like this. There’s other ones, ultimatum
game, there’s a trust game. It’s the same notion
of business there, which is you choose to
cooperate, you choose to cheat, what’s the optimal outcome. There are mathematically optimal
outcomes that you can use, and you run all of it
against the computer, and you get the optimization
popping out the other end. Wonderful. So there’s Axelrod and
his buddies using terms like oh, this
strategy will drive the other one into extinction. Or this strategy works,
but if you program in that every now and then
there could be a glitch, there can be a mutation,
this will be– they’re using all this biology jargon,
obviously metaphorically. But right around this
point, the biologists look at this, who are
just beginning to think about the social biology stuff. Formal patterns of
optimizing behavior. And they say whoa, does
this apply to the behavior of real organisms? Because at this point, it’s just
economists and computer types and diplomats learning
when to optimize, all that sort of thing. Around the time there
was a paper published, somewhat before that. This is a name nobody
is going to know, lost in history, a guy
named Daniel Ellsberg. Daniel Ellsberg became
very famous around 1970, by he was working
in the Pentagon and he stole thousands
of pages of secret files there, and gave it
to the New York Times showing how utterly
corrupt everything that went on behind the scenes was
in getting us into Vietnam. Major blowout, all of that. He had spent the early part of
his career perfectly happily working in the Pentagon for the
military as a game theorist. As a game theorist coming
up with optimal patterns. And he wrote one paper
called “The Optimal Benefits of Perceived Madness”. What times do you
want your opponent to think you are
absolutely out of your mind and going to do all
sorts of crazy stuff, and where they
wind up cooperating to keep you from doing that. The advantages of
madness, what’s that. That’s systems where things like
mutually assured destruction doesn’t work, because you
are willing to set it off. The advantages of madness. This whole world of people
working on it, mathematicians and war strategists. And there’s the zoologists now
looking at this saying whoa, this is cool. I wonder if animals
behave that way. And that’s when people, now
armed with their insights into prisoner’s dilemma
and tit for tat, all this stuff, started to
go and study animals out in the wild and see, were
there any examples where this happened. Yes. In all sorts of
interesting realms. First example, vampire bats. Vampire bats, we are all
set up to be creeped out by vampire bats. But in actuality, when you
see a vampire bat drinking the blood of some
cow or something, you are watching a mommy
getting food for her babies. Because vampire bat
mothers are not actually drinking the blood. They’re filling up
this throat sack thing, and they go back to the
nest and they disgorge the blood to feed their babies. She’s just watching
out for her kids. It happens that vampire bats
have an interesting system of reciprocal altruism, which
is a whole bunch of females will share the same nest. Will have all their
kids in there mixed in. And these are not
necessarily related, so we’ve just left the
world of kin selection. They’re not necessarily
related, but they have reciprocal altruists system. Each female comes in,
disgorges the blood, and feeds everybody’s babies. And they all feed
each other’s babies, and everything is terrific. And they have this blood
vampire commune going there. And they’ve reached a nice
state of stable cooperation. Now, make the bats think
that one of the females is cheating on them. Out comes that female flying off
to find some blood, and instead you net her and
get a hold of her, and take some
syringe full of air and pump up the throat
sack so the throat sack is really
full and distended, but there’s no blood in there. You’ve just pumped
air into there. And stick her back
into the nest there. And she’s just
sitting there happily, and the other
females are sitting saying look at her, look at
how much blood she’s got there. I can’t believe it, because
she’s not feeding our kids. She’s cheating on us. And the next time
they go out to feed, the other females
don’t feed her kids. A tit for tat. What you saw here
is an exact example of introducing signal error. Signal error, in this case,
being some grad student pumping up the throat
of some vampire bat and showing that they’re using
a version of a tit for tat strategy. Totally amazing. People were blown away by this. Another example, fish. Stickleback fish who, in the
world of animals– you know, bats are probably not some of
the brightest folks around. But I don’t think sticklebacks
are within light years of them. But stickleback fish can
do a tit for tat strategy. Here’s what you do. You have a stickleback
fish in your fish tank, and you make the fish
believe that he’s being attacked by another fish. What do you do? You put a mirror up against
the edge of the tank there. So within a very short
time– I told you they were not that smart. So within a very
short time, he’s lunging forward at
this mirrored thing and maintaining his
territory against this guy and barely holding on. And that other guy is
just– he doesn’t get tired. Thank god I don’t get tired. And they’re just going at it. And now make him think he
has a cooperative partner. Put in a second mirror
that’s perpendicular here. In other words, he sees
his reflection there. And every time he
moves forward, the sees that one moving
forward, which is fortunate because he’s also seeing another
fish coming from that way. And he’s sitting there
saying, this is great. I don’t know who this guy is,
but wow, what a team we are. [LAUGHTER] Doubles, this is great. He’s in there and the thing
is, it’s funny how those two guys are so synchronized. But whoa, we’re holding
them off and we’re doing it. Now make him think his
cooperating partner is, in fact, cheating on him. Take the mirror and
angle it back a little bit so the reflection
is set back some. And what he now sees is
the fish moving forward, but not all the way
up to the wall there. The fish is hanging back there. The fish is cheating. And this stickleback is sitting
there saying, in effect, that son of a bitch. I can’t believe he’s
doing that to me. We’ve worked together for years. I can’t believe he’s– oh
he’s pretending to go forward. But I see he’s not
really doing that. Fortunately, that guy isn’t
coming forward anymore, either. Phew. But I can’t believe
the guy is cheating. And the next time you set up
this scenario, the next time there’s a chance the
stickleback doesn’t attack its own reflection there. It is tit for tatting
against this guy. So here we’ve managed to
set up one of these deals within one fish and
carrying it out forever. One fish, ultimately with
some very blistered lips. Tit for tat, once again. Another example. This is the most bizarre
one I can imagine, and leads to all sorts of
subjects that are going to come many lectures from now. But there are fish species
that will change sex. And they do it under all sorts
of strategic circumstances that suddenly begin to fit
into this realm of what we’ve been learning about. And you’ve got one of these
things called black hamlet fish. And they can change gender. So you’ll have a
pair of them who hang out with each other
of opposite genders, and they take turns. They flip back and forth. For a while, this one’s
female, and for a while, this one’s female. And they go back and
forth, and that’s great. But there’s an
inequity there, which is that the price
of reproduction is greater for the
female than for the male. As is the case in
so many species, the female doing all
that egg and ovaduct and progesterone stuff,
or whatever it is. And the male’s just got to
come up with some sperm there. Doing to reproduction
as a cooperating pair, they’re not relatives. Reciprocal altruism, maximizing
each of their reproductions. Whoever’s the female
in any given round is the one who’s paying more. What you see are reciprocal
relationships there of the fish using tit for tat. If you get one fish that
begins to cheat and winds up being a male too
much of the time, the other fish stops
cooperating with them. Again, tit for tat stuff. So people were just blown out
of the water at this point, seeing whoa, forget rational
human economic thinking, all of that. You go out into the wild,
and bats and stickleback fish and gender switching
fish and all of that, they’re following some of
the exact same strategies. Isn’t nature amazing. No, nature isn’t amazing. It’s the exact same
logic as saying a giraffe has to
have a heart that’s strong enough to
pump blood to the top of the head of a giraffe. Or else there
wouldn’t be a giraffe. And when you look at this realm,
it’s applying the same notion. This same sort of wind tunnel
of selective optimization for behavior– in this
case, when to cheat, when to cooperate–
sculpts something that is as optimized
as a giraffe’s heart being the right size. So this made perfect sense. Wonderful. But then people began to
look a little bit closer, and began to see the very
distressing real world beginning to creep in there. Which were exceptions. First exception. This was done by a guy named
Craig Packer, University of Minnesota, looking
at lions in East Africa. What you get is,
typically, prides are a whole bunch of relatives,
usually female, sisters, nieces, all of that. But you will sometimes
get prides that are not of close relatives. Nonetheless, they will get
reciprocal altruistic things going on. Lions, in this case,
having the same trick as was done on those
vervet monkeys. Researcher putting inside
the bush there a speaker, and playing the sound of like
400 menacing lions all at once. What you’re supposed to do
is freak out at that point. And all of you need to very
carefully approach and see what’s going on in that bush. So what would happen
in a reciprocal system, and everybody does this. Or if one time, one
of them cheats on you, you push that one
forward the next time. Or some such thing. That’s what you would expect. But what he would
begin to notice is, in a bunch of these groups,
there’d be one scaredy cat lion, one who habitually
stayed behind the others and who wasn’t punished for it. So this produced
this first puzzle that oh, sometimes animals
aren’t optimizing tit for tat. Sometimes animals haven’t read
Robert Axelrod’s landmark 1972 paper, that sort of thing. And what you suddenly
have is the real world. What could be
possible explanations? One thing being, maybe they’re
not really paying attention. Maybe they’re not
quite that smart. Wait, bacteria are doing
versions of tit for tat. What else could be going on? Oh, lions interact
in other realms. Maybe this individual is
doing very reciprocal stuff, forgiving overly altruistic
stuff in some other realm of behavior. Maybe this lion eats
less of the meat and backs off earlier,
or something like that. Maybe there’s another game
going on simultaneously. And this is introducing
the real world in which it is not
just two individuals sitting there playing prisoner’s
dilemma and optimizing. You suddenly begin to get
real world complexities coming in there. And by the time we
get to the lectures, way down the line, on
aggression and cooperation, what you’ll see is things
get really complicated when you have individuals
playing games simultaneously. The rules that you apply
to one psychologically begin to dribble
into the other one. All sorts of things like that. It will get very complicated. So a first hint there
that, in fact, everything doesn’t work perfectly
along those lines. Here’s another version. Here’s one of the truly
weird species out there, something called
the naked mole rat. If you ever have
nothing to do and you’ve got Google Image up there, go
spend the evening looking up close up pictures
of naked mole rats. These are the weirdest
things out there. They are the closest
things among the mammals to social insects, in terms
of how their colonies work. They’re totally
bizarre, all of that. But they live in these
big, cooperative colonies that are predominately
underground in Africa. And they were discovered, I
think, only in the 1970s or so. And for a while when
zoologists got together, if you were a naked
mole rat person, you were just the
coolest around. And everybody else
would feel intimidated, because you were working on
the best species out there. And you would see these
big cooperative colonies, soon shown to not
necessarily be of relatives. And reciprocity and all
those sorts of rules. But people soon
began to recognize there would be one or two
animals in each colony that weren’t doing any work. Work digging out
tunnels, bookkeeping, I don’t know what naked mole
rats do in terms of work. But there would be a
few individuals who would just be sitting around. And they were these big
old naked mole rats. They were much bigger
than the other ones, and they were scarfing
up food left and right. There goes Robert
Axelrod down the drain. There goes all
that optimization, because no one would be
punishing these guys. What’s the deal? And it took enough watching
these animals long enough to see this notion
of oh, there’s another game going
on in which they play a more important role. And it is sort of
dribbling across. When the rainy season comes,
these big naked mole rats go up and turn around and they
plug the entry to the tunnels then. [LAUGHTER] That’s what they do. And suddenly,
these guys who have been sitting around doing
no work whatsoever all year and eating tons of stuff, they
suddenly have to now stick their rear ends out for
the coyotes to be around or whatever it is
that predates them. What we have is role
diversification. Real animals, real
organisms, are not just playing one formal prisoner’s
dilemma game against each other at the same time. And by the time we, again,
get to the later lectures on aggression,
cooperation, all of that, we will not only see that things
get much more complicated when you’re playing
simultaneous games, when you’re playing a game
against one individual while you’re playing
against another one, and then against
triangular circumstances. How play differs if you
know how many rounds you are playing against
the individual versus if you have no idea. How play differs
if, when you are about to play
against someone, you get to find out what
their behavior has been in the previous trials
with other individuals. In other words, if somebody
shows up with a reputation, we’ll see this is a much
more complicated world of playing out these games. A much more realistic one. So we begin to see a first pass
at all this optimization stuff, and how great that all is. One final interesting addition
to this game theory world of thinking about behavior like
that, which came from a guy named James Holland,
who apparently– might have a different first name. But Holland, apparently, as an
interesting piece in history, he’s the person first
person to ever get a PhD in Computer Sciences. Which I think was in the late
50s, University of Michigan. Apparently, there are realms
of computer programmers who worship this guy. And he, like a lot of other
folks in that business, got interested in this
game theory evolution of optimal strategies. And he designed ways
of running all of this. And he introduced
a new ripple, which is the possibility of a
strategy suddenly changing. The possibility of a mutation. What he could then
study was mutations, how often they were
adaptive, how often they spread throughout the strategy
there, of individuals playing. How often they drove
the other strategies into extinction versus
ones that were quickly driven to extinction themselves. More cases where we are
getting these systems where maybe they’re not just
metaphorically using terms from biology. Maybe they are exactly
modeling the same thing. And we will see more and
more evidence for that. OK, so reciprocal altruism. How would that play out in the
world of natural selection. Natural selection,
cooperative hunting. And there’s lots of species
that have cooperative hunting. Wild dogs, jackals, some
other species as well. Clearly, that’s
like the definition of cooperative hunting,
of reciprocal altruism, if they’re not relatives. How would sexual
selection play out in the realm of
reciprocal altruism? A little bit less obvious there. That would be if you
and some non-relative spent an insane amount
of energy and time making sure you both look really
good before going to the prom. That would be sexual selection
working on reciprocal altruism system. So what we have now are
three building blocks. This whole trashing of it’s
not survival of the fittest. It’s not behaving for
the good of the species. It’s not behaving for
the good of the group. But instead, these
three building blocks, the ways to optimize
as many copies of your genes in the next generation
as possible. Way number one,
individual selection, a version of selfish genes. Sometimes a chicken is an egg’s
way of making another egg. Behavior is just a way of
getting copies of genes into the next generation. Piece number two, inclusive
fitness kin selection. That whole business,
that sometimes the best way of passing on copies
is to help relatives do it. And it’s a function of
how related they are. The whole world of cooperation
more among related organisms than unrelated ones. And as we will see way
down the line, what is very challenging
in different species is, how do you figure out
who you are related to? And humans do it in a very
unique way that sets them up for being exploited in all
sorts of circumstances that begin to explain why culture
after culture, people are really not nice to thems,
and it flows along those lines. This is something we will
get to in a lot of detail. So degree of relatedness,
a lecture coming. How do you tell who
you’re related to. But that second
piece, kin selection. Third piece,
reciprocal altruism. You scratch my back and
I’ll scratch your back. And whenever possible, you want
to instead scratch your back, and they want to
make sure you’re not scratching your back. Or whatever cheating counts as. But trying to cheat,
being vigilant against it, formal games where you can
optimize it, very complicated. And can you believe it, you
go out into the real world, and you find examples
of precisely that. Optimization with tit for
tat, isn’t nature wonderful. It’s gotta work that way. Then you begin to see how the
real world is more complicated. Multiple roles, naked mole
rats stuck in plumbing, things of that sort. These are the principles. And what people of this
school of evolutionary thought would say, armed with
these sorts of principles, you could now look at all
sorts of interesting domains of animal behavior
and understand what the behavior is going
to be like by using these. OK, we start with
the first example. Here we return to these guys. And we have one species
here, and knowing this guy had a penis
and this one nursed, we’ve got an adult male
and an adult female. What is it that
you can conclude? In this species, males are
a lot bigger than females. Let’s state it here as there’s
a big ratio of males to females. Meanwhile in the
next county, you’ve discovered another species
where somebody’s got a penis and somebody else is nursing. And their skulls are
the exact same size. Oh, here’s a species
where there’s no difference in body size
between males and females. Let’s begin to see, just
using the principles we’ve got in hand already, what
sort of stuff we can predict. Starting, which of those
species– in one case, you have males being a
lot bigger than females. In one case, you’ve got males
being the same size as females. In which of those species,
the first one like this, or the same size
ones, which ones would you expect to see
more male aggression? First one. First one. OK, how come? Their bodies are built for it. Their bodies are built for it. Which begins to
tell you something, their bodies are
built for it, maybe because females have
been selecting for that. You will see higher
levels of aggression in species like this, where
there’s a big body size difference, and much
less of it in these guys. Next, you now ask how
much variability is there in male reproductive success. In one of these
species, all the males have one or two kids
over their lifetime. In another species,
95% of the reproducing is carried out by
5% of the males. A huge variability skew in
male reproductive success. Which species do you
get the every male has a couple of kids, and that’s
about it, and all equally so? Which one? [INAUDIBLE] Second one. How come? Because these guys are being
selected for aggression. If they’re fighting,
there’s going to have to be something
they’re fighting for. Deferential reproductive access. OK, so you see more variability
in species that look like this. Next, females come
into the equation. What do females want? What do females want in
the species on the left versus the one on the right? The one on the
right, again, skull’s the same size, same body size. On the left, what
does the female want? [INAUDIBLE] What sort of male is the
female interested in? [INAUDIBLE] Big. Exactly. That’s exactly the
driving force on this. How come? Because she’s not going to get
anything else out of this guy. This guy is just going
to, like– the present is going to be some sperm. It might as well be some
good sperm, some genetically well-endowed sperm that makes
her a big healthy offspring, increasing the odds of her
passing on copies of her genes in the next generation. What about in this species? What’s females looking for? [INAUDIBLE] OK, good. Hold on to that for
a second, and let’s jump ahead a few lines. One of the species,
males have never been known to do the slightest
affiliative thing with infants. They just get irritated and
harass them and all of that. In the other, you
have soccer dads who are doing as much raising
of the kids as the females are. In which species do you get
lots of male parental behavior? Smaller. The one on the right. OK. So lots of male
parental behavior here. Somebody just gave the
answer here, female choice. What would you see
in this species? You want big, muscular guys. You want whatever is
selling that season for what counts as a hot male, because
you want your offspring to have those traits. And somebody else
called out here, what do females want
in this category? And what was it you said? Good personality. [LAUGHTER] Good personality. Yes. Able to express emotions. [LAUGHTER] That, too. OK, somebody else
shouted out something that gets at the broader,
more globally Oprah version. OK, somebody shouted out– [INAUDIBLE] –parental behavior. You want a male who is going
to be competent at raising your children. What is it that you
want, really most deeply? You want to get the male who
is the most like a female you can get a hold of. You don’t want some
big old stupid guy with a lot of muscle and canines
who’s wasting energy on stuff like that he could be using
instead on reading Goodnight Moon or some such thing. What you want
instead is somebody who’s as close to a female as
you can get to without getting this lactation stuff. Males are chosen who are
the same size as females. So the term given here is
choosing for paternal behavior, parental behavior. Parental, let’s just
put that in there. And that begins to explain
the top line, species in which there’s a lot
of sexual dimorphism. Morphism, shapes of things. Sexual dimorphism,
big difference in body size as a
function of gender. And in these sorts
of species where you get male parental
behavior, not much variability in male
reproductive success, low levels of
aggression, and what females want is
a competent male. These are ones where you see low
degrees of sexual dimorphism. So how’s a female
going to figure out that this guy is going
to be a competent parent? Once again, we just figured out,
if he looks kind of like you. Because that suggests he hasn’t
wasted health and metabolism on stupid, pointless
muscles when there’s more important things
in life for making sure your kids have good values. What else would the female
want to know when she’s first considering mating with a male? Is he a nice guy,
is he sensitive, does he express his feelings. Is he competent
at being a parent. What do you want the
individual to do? Prove to you that he can
provide for the kids. And suddenly you have a world of
male birds courting the females by bringing them worms. Bringing them
evidence that they are able to successfully forage,
they are able to get food. Female choice is built
around appearance and behavioral
competence at being able to be a successful
parent in order to pass on as many
copies of genes to the next generation
as possible. OK, how about life span. In which species is there a big
difference in life expectancy as a function of gender? First one. First one. Here you’re choosing
for males to be as close to females as possible,
and thus the physiology. Here you’ve got
these guys who are using huge amounts
of energy to build up all this muscle, which
takes a lot more work to keep in calories. And you’re more
vulnerable in famines. You’ve got these males
with high testosterone, which does bad stuff to
your circulatory system. You’ve got males who, thanks
to all this aggression, are getting more
injuries, more likely. In species in which you have
a lot of sexual dimorphism in body size, you get a lot of
sexual dimorphism in life span. Then you look at these
guys, and it’s basically no difference by gender. Moving on. Considering primates
that are one of these two patterns, in
which one do you always want to give birth to twins,
in which one do you never want to give birth to twins? Who gives birth to twins? [INAUDIBLE] The one of the right, of course. How come? Because you’ve got two
parents on the scene. You are not a single mother. And you are a single mother
rhesus monkey or something, and you give birth to
twins, and you do not have the remotest
chance of enough energy, enough calories on board, to
get both of them to survive. A twin that is born
in a species like this has the same rate that it occurs
in humans, about a 1% rate. And it is almost inevitable that
one of them does not survive. Meanwhile, there’s a whole
world of primate species with this profile where
the females always twin. Finally, you are
the female and you are contemplating
bailing out on your kids and disappearing,
because there’s some really hot guy over there
who you want to mate with. And you are trying to
figure out this strategy. So you are going to leave
and abandon your kids. In which species do
you see that behavior? The one on the right. The one on the right, because
you bail out and the male is there taking care of them. You bail out in here, and you’ve
lost your investment and copies your genes for the
next generation. You see female cuckoldry,
this great Victorian term. You see females cheating on
the fathers in this species, but not in species like this. Because the father is long gone
and three other counties there, courting somebody else. And it doesn’t
matter, you’re not going to get any help from him. In primate species
of this profile, you always see twinning. And they both survive. And what studies have
shown in these species, and we’ll get to
them shortly, is after birth, in fact, the males
are expending more calories taking care of the
offspring, then the females go bail out on him
and go find some other hot guy. Which, in your species,
counts as some guy who looks even more like you
than he does in terms of what you want out of the individual. So that. So what have we done here? We’ve just gone through
applying these principles in this logical
way, and everybody from the very first step was
getting the right outcome. And go, and these are
exactly the profiles you find in certain species. Among social mammals,
these would be referred to as a tournament species. A tournament species,
whereas the one on the right is referred to as a pair
bonding, a monogamous species. Because in this one,
males and females stay together, because they
both have equivalent investment in taking care of the kids. All of that. What you have here
is this contrast between tournament species
and pair bonding species. Tournament species,
these are all the species where you get males with
big, bright plumage. These are peacocks,
these are all those birds and fish species where the
males are all brightly colored. What are the females
choosing for? Peacock feathers does not make
for a good peacock mother. Peacock feathers are signs
of being healthy enough that you can waste
lots of energy on these big stupid
pointless feathers. That’s a sign of health. That’s a sign of all I’m getting
from this peacock is genes, I might as well
go for good ones. That’s the world
of peacocks, that’s the world of chickens
with pecking orders, dominating like that,
lots of aggression. That’s the world of primates
where, as in savanna baboons, the male is twice as
big as the female. Tournament species, where a
lot of passing on of genes is decided by male-male
aggression in the context of tournaments producing
massive amounts of variability in reproductive success. Where males are being selected
for being good at this, so they sure are being selected
for having big bodies, which winds up meaning
a shortened life span for a bunch of reasons. Females are choosing for that. These are guys who are
not using their energy on parental behavior,
thus you do not want to have twins if
you are a female baboon, and you do not want to
bail out on the kids because nobody else is
going to take care of them. Go and look at a
new primate species, and see this much of a
difference in skull size, and you’d just be able
to derive everything else about its social behavior. Meanwhile, these guys on the
right, pair bonding species. These are found among South
American monkeys, marmosets, tamarins. You put up a picture
of them, which I will do if I ever
master PowerPoint in some subsequent
lecture– you put up a picture of a marmoset
pair, and you can’t tell who’s the male and the female. This is not the world
of the mandrill baboons, with males with big, bright,
bizarre coloration on the face, and with antlers when
the females don’t, and that whole world
of sexual dimorphism. You can’t tell which
one is the male and which one is the female
marmoset by looking at them. You can’t tell by seeing
how long they live. You can’t tell by
how much they’re taking care of the kids. You can’t tell in terms of
their reproductive variability. That’s a whole different
world of selection. All of the South American
tamarins and marmosets, the females always twin. They have a higher
rate of cuckoldry, of abandoning the kids. The males take as much
care, if not more, of the kids than
the female does. Very low levels of aggression. Same body size, same lifespan. All the males have low
degree of variability. How come? Because if you’re
some marmoset male, you don’t want to get 47
marmoset females pregnant. Because you are going to have
to take care of all the kids. Because as we will see way
down the line in lectures on parental behavior,
the wiring there is such is bonding with the offspring
and taking care of them. No wonder among
species like these, you have very low variability. All the males reproduce
once or twice. This is the world of 5%
of the guys accounting for 95% of the matings. This is totally
remarkable because again, that starting point. You start off here,
and you look at these, and oh, you can tell if
they were bipedal and were they diseased or malnourished,
simply by applying these principles of individual
selection, reciprocity, all of that. One factoid, you see
a new primate species, and you see one nursing
and one with a penis, and they’re the same size or
there’s difference in the size, and you already know all
about their social system. Very consistent across birds,
across fish, across primates. Of course, all of
those, this dichotomy between tournament species
and pair bonding species. As we will see
way down the line, among some species,
types of voles, rodents, that are famous in Hallmark
cards for their pair bonding, for their monogamy. As we’ll see, they’re
not quite as monogamous as you would think. But nonetheless, a general
structure like this. So, one asks expectedly, where
do humans fit in on this one? Where do humans fit? And the answer
is, complicatedly. Are we a tournament species,
are we a pair bonding species. What’s up with that? What we will see is
we’re kind of in between. When you look at the degree
of sexual dimorphism, we are not like baboons, but
we’re sure not like marmosets. We’re somewhere in the middle. Variability is somewhere
in the middle there. I’m not going near that one. Life span, the
dimorphism in lifespan tends to be in between. Parental behavior and
likelihood– all of those, you look at a
number of measures. And by next lecture,
we’ll be looking at some genetics of what
a monogamous species and tournament
species look like. And we’re right in the middle. In other words, that explains
like 90% of literature. Because we’re not a classic
tournament species and we’re not a classic pair bonding one. We are terribly confused
in the middle there. And everything about
anthropology supports that. Most people on the
planet right now are in a form of
monogamous relationships in a culture that
demands monogamy. An awful lot of people who are
in monogamous relationships in such cultures aren’t really
in monogamous relationships. Traditionally, most cultures on
this planet allowed polygamy. Nonetheless, in most of
those polygamous cultures, the majority of individuals
were pair bonded and monogamous. You get two different
versions of polygamy in different social
systems of humans. One is economic polygamy,
which is you’re basically sitting around, and the
wealthiest guy in the village is the one who can have the
largest number of wives. An enormous skew in
reproductive success that’s driven by economics. The other type is demographic. You have a culture
where, for example, you have a warrior class. Guys spend 10 years as
warriors– worriers, warriors, New York City accent. As warriors, they don’t worry. There’s no anxiety. But they eventually worry
about getting a wife, because by the time they’re
done being a warrior, they’re like 25. And they marry someone
who’s 13, which is what you see in a lot
of traditional cultures that follow that pattern. And at that point,
you’ve got a problem, which is an awful lot of
those guys have been killed over the course of 10
years of being involved in high levels of aggression
and 10 more years of life expectancy to catch up with you. There’s is a shortage of males. So you see polygamy there
driven by demographics, and you see polygamy
driven by economics in other types of society. So most cultures on this
planet allow– traditionally, before the
missionaries got them– most cultures on this
planet allow polygamy. Nonetheless, within most
polygamous cultures, the majority of people
are not polygamous. We have one really confused,
screwed up species here. Because we are halfway in
between in all sorts of these measures. OK, so what do we
have next, which we will pick up on Friday. What we’ve just
started with here is the first case of using
all these principles, individual selection, kin
selection, reciprocal altruism, to understand all sorts
of aspects of behavior. We will then move
on to seeing how they explain other aspects
of animal behavior, some ones which, if you are behaving for
the good of the species circa 1960, there’s no explanation
at all, because you’re doing things like killing
other members of your species. And then finally,
we will see how this applies to humans and
some of the witheringly appropriate– For more, please visit
us at stanford.edu.