Prof: Okay,
I think it's probably
appropriate that the course
finishes on this note.
These are some of the most
interesting and most nuanced and
deepest issues that we've
addressed in ecology and
evolution,
and they bring all these fields
together: evolution,
ecology and behavior.
So the outline of the lecture
is given here,
and basically what I'm going to
tell you is that the initial
idea on how altruism and
cooperation could evolve was kin
selection;
later alternatives were
proposed, and the current
situation is a bit more nuanced.
We currently have pretty good
explanations for why unrelated
individuals can cooperate.
 
You've seen a bit of that
perhaps with the vampire bats,
and you'll see some more
examples in other cases.
Now, this line of research was
really provoked by Darwin's
honest admission;
something that I think every
transparent and intellectually
honest scientist ought to do.
He stated the conditions under
which he should be willing to
abandon his theory.
 
If ever it could be shown that
individuals repeatedly and
reliably sacrificed their own
fitness to increase the fitness
of others,
the theory of natural selection
would be refuted.
 
Well, naturally that attracted
attention.
The logic is given here,
and the conclusion that one
would come to from that is that
if you just take a simple-minded
view,
mid-nineteenth century view,
of the theory of natural
selection,
altruism and cooperation should
be impossible.
And an early alternative
explanation focused on group
selection, and the iconic
example there was the red grouse
in Scotland;
it's a kind of ptarmigan.
And the group selection claim
was that they would curtail
their reproduction to keep their
population from over-cropping
the food supply and thereby
preserve the population as a
whole.
 
And so the issue was why
shouldn't an individual reduce
reproduction?
 
Why should one not reproduce
reproduction and thus avoid
over-exploiting the food supply?
 
And the problem is that if you
look at the decision made by any
single individual,
it's benefiting the whole
population,
but at the cost of its own
offspring.
 
Okay?
 
And everybody benefits,
but the costs are paid by that
single individual.
 
And so any selfish individual
who decided to defect,
who wouldn't reduce its
reproduction,
would benefit.
 
The others would cut back,
it would get more.
And so group selected altruism,
as we've seen from evolutionary
game theory, is not going to
invade when rare.
It's not an evolutionarily
stable strategy,
and it doesn't resist invasion
by selfish alternatives.
So the group selection
explanation is logically faulty.
That doesn't mean that group
selection never works;
we'll pretty soon state the
conditions under which it might,
but it certainly doesn't work
in this case.
So this is very similar to the
tragedy of the commons.
And the reason that the red
grouse reduce their reproduction
when the population is dense,
I think you already know.
Can anybody tell me why?
 
Population density goes up,
what happens to fertility,
and why?
 
Yes?
 
Student:
>
Prof: Right, exactly.
 
They have a very straight
physiological response to that.
Population density goes up,
they have less to eat,
they can't make as many babies.
 
That's why the red grouse don't
make as many babies in the fall,
when the population is dense.
 
So let's go back to the basics,
to see what the critique of
group selection is.
 
Because this had to be worked
through before people could
really understand it and abandon
it and seek other alternatives.
We're back to day one of the
course;
we're on the last day of the
course, we're going back to day
one.
 
So if there's any selection
process going on,
its ability to produce change
is determined by how much
variation in reproductive
success there is,
among the things being selected;
by the correlation between the
trait under selection and the
variation in the success of the
unit,
which would be in this case
either an individual or a group,
a whole population of red
grouse;
and the genetic variation of
the trait among the units.
 
Well let's just step through
all of those conditions.
Usually the correlation between
a trait and reproductive success
is much stronger for the
individual agents for the group
than for the group in which
they're embedded.
And you have to think of the
reproductive success of an
individual as being its
offspring,
and the reproductive success of
the group as being the number of
groups that it might found.
 
The variation in reproductive
success itself is greater among
individuals than among groups,
usually, and that's
primarily--I mean,
you can just see it
statistically.
 
You're taking--the reproductive
success of the group is going to
depend upon the average of the
reproductive successes of the
individuals in it,
and so normally the variation
will be greater among the
individuals than it would be
among the groups.
 
The amount of genetic variation
in a trait that could be
accounted for by differences
among individuals is also a lot
larger.
 
So inter-individual variation
is usually much greater than
variation among groups.
 
We saw that,
by the way, when we did the
analysis of genetic variation
among ethnic groups and we saw
that 85% of human genetic
variation is among individuals,
and only about 15% is elsewhere.
 
The generation time of
individuals is a lot shorter
than that of groups.
 
When you get into things like
species selection--remember,
the average lifetime of a
species is one to ten million
years.
 
If you want to talk about
reducing the extinction rate of
species on the basis of group
selection,
you've got a real problem,
because you only get a
selection event once every
million years to once every ten
million years.
 
So anything that's cranking
along at the level of the
individual is going to happen
many,
many, many times before a
single event will happen at the
level of a group.
 
And that is this final point,
which is the number of
incidents of selection on
individuals, in any given unit
of time, is normally much,
much greater.
Okay?
 
So it's the combination of
these six conditions that makes
it possible for a selfish mutant
to invade a resident population
of self-sacrificing altruists.
 
So that's the more precise
analysis of why the original
nineteenth century Darwinian
theory said we expect
individuals to be selfish.
 
But look what we find.
 
We find communal colonial
living, group hunting and
sharing food,
alarm calls,
reproductive helpers;
you just saw three examples of
them in the video.
 
And these are the leading
alternatives to group selection:
kin selection,
punishment, and mutualism.
So let's go through them.
 
The basic idea of kin selection
I think you're already familiar
with.
 
It has interesting and
unsettling philosophical
implications.
 
If what matters isn't the
survival of the adult phenotype,
of the whole organism,
but an increase of frequency of
genes that that individual
carries,
then it will pay for that
individual to sacrifice itself
if more copies of its genes get
into the next generation than if
the individual did not sacrifice
itself.
So the costs and benefits have
to be weighed in genetic
currency.
 
The genes are not only in it,
but they're also in its
relatives.
 
So if it can help its relatives
to survive and reproduce then--
and if the increase that it
gets by doing that is greater
than the cost that it suffers by
doing that--
then that behavior will be
selected.
So to formalize that,
just that the benefit is the
increase in the relative's
fitness, as a result of the act.
The cost is the decrease in the
donor's fitness.
R is the coefficient of
relationship.
So you are .5 related to full
sibs, .5 related to mom,
.5 related to offspring.
 
Then calculating out:
.125 to first cousins and
things like that.
 
That's what R is.
 
And that is calculated as the
probability that a gene in the
donor and a gene in the
recipient are so-called
identical by descent from a
common ancestor.
So R varies between 0 and 1.
 
Then the condition for helping
is that B divided by C is
greater than 1/R,
or the benefit times the degree
of relationship is greater than
the cost.
Or to put it into words,
the increase in the relative's
fitness as a result of the act,
times the relationship to the
relative--
right here--is greater than the
decrease in the donor's fitness
as a result of the act,
times its relationship to
itself;
which is 1.
 
Okay?
 
So that is a very simple
inequality, and it's a very
powerful idea.
 
This is the guy that had it;
this is Bill Hamilton.
And Bill is a remarkable man.
 
He died in 2000,
after having--I think I've told
you--
after having gone to the Congo
to see whether or not AIDS got
into humans through a polio
vaccine.
 
And he was a very creative and
iconoclastic scientist;
certainly one of the major
minds in evolutionary biology in
the last hundred years.
 
Now some of the traits that
people think might be kin
selected are alarm calls,
guarding behavior,
helping at the nest,
and suppressed reproduction.
By the way, if you printed out
the lecture,
I've taken out the two slides
on social hymenoptera,
just to save a little time,
because I wanted a little more
time for Sir David.
 
And I'm not really sure I'm
going to get through all of
this.
 
But these are the kinds of
things that people think can be
explained by kin selection.
 
So one of the early ones was
the contrast between ground
squirrels and marmots.
 
And this is based on a
difference in their social
organization,
and in the probability that a
given sex will be close to
relatives.
So in the ground
squirrels--these guys live in
Yosemite--
the males wander off,
the females stay near their
burrow,
and it's the females who give
alarm calls,
and they usually do so when
offspring are threatened,
and sometimes they give alarm
calls when a niece is
threatened.
 
And that's because the females
don't move so far,
and the daughters and nieces
and so forth are living in
adjacent burrows.
 
So an adult female will watch
and will give the alarm call.
It's quite different in marmots.
 
In marmots they hold harems.
 
The male who is sitting on a
pile of rocks,
with a bunch of females in it,
knows that all the babies in
that pile of rocks are his own.
 
And so in this case it is the
male that is giving the alarm
call.
 
And the contrast between the
two species--I think you can see
some of the power of the
comparative method here.
They're very similar in their
biology otherwise,
but in one case the male gives
the call and in the other case
the female gives the call,
and the contrast tells you that
it seems to be pretty tightly
associated with how close they
are in space to their offspring.
 
So you might want to consider
whether or not this evidence of
parental care really is evidence
of kin selection,
or is it simply the act of the
individual completing
reproduction.
 
So I'll leave that up in the
air.
But this is some of the early
evidence that was used.
Now perhaps a little bit more
convincing are helpers at the
nest.
 
There are quite a few birds in
which there are helpers at the
nest.
 
Here are four of them;
so Pied Kingfisher,
Florida Scrub Jay,
Acorn Woodpecker,
and White-fronted Bee-eater.
 
We'll do the Pied Kingfisher
example, which was done by Ueli
Reyer.
 
And he did this in East Africa,
contrasting colonies living on
Lake Victoria and Lake Naivasha.
 
So basically the reason he
contrasted them is that one of
them has rough water and one of
them has smooth water.
And when the water is rough
it's harder to hunt and you need
more help to feed your babies,
and when the water is smooth
it's easier to hunt and you
don't need so much help to feed
your babies.
 
And indeed the percentage of
nests with no helpers was higher
at Lake Naivasha,
with smooth water.
Primary helpers were not so
frequent.
Primary and secondary helpers
were pretty rare;
almost no secondary helpers at
all at Lake Naivasha.
Primary helpers are older sibs
and secondary helpers are
unrelated birds.
 
And these are the proportions
of encounters in which mated
males are attacking or greeting
potential secondary helpers.
So this relates for unrelated
birds coming into the nest.
Do they attack them or greet
them?
And if you have two to three in
the nest,
they usually get attacked at
Lake Naivasha,
but if you have four or five
babies,
and you really need help,
then they are greeted.
And at Lake Victoria,
with two to three in the nest,
they are greeted,
and if you have a reduced
clutch they get attacked.
 
So this was a case in which
there was a clutch manipulation.
So basically if you need help
you greet helpers,
and if you don't need help you
chase them away.
And what's going on here is
that there's both degree of
relationship for the primary
helpers who are sibs,
but then there's also the issue
of can I get a nest site?
And why is it if I'm not
related to these guys am I
helping them out?
 
And the answer is that the
helpers inherit the nest sites.
So nesting is done in cliffs.
 
There's not very much available
cliff habitat.
They dig a meter-long burrow,
which is a lot of effort,
back into the cliff--so if you
can take one of these over,
you don't have to dig it
yourself--and they lay their
eggs way at the back of the
burrow.
So there's an ecological
constraint on the system,
and it's interacting with
degree of relationship.
So overall, if you look at
total fitness of the different
kinds of roles that are being
played in the population--
the breeding birds,
the primary helpers,
the secondary helpers,
and those not helping--
and you calculate both direct
fitness and indirect fitness
through relatives,
over the lifetime of the
birds--so this takes years to
gather;
this is a summary of a lot of
work--mating is better than
helping.
 
We see that here.
 
Helping's better than not
helping, because it puts you in
a position to inherit a nest
burrow.
If you do help,
it's better to help a relative
than a non-relative.
 
And if you are a breeding bird,
you only should accept help if
you really need it,
because the helpers might get a
little frustrated and restless
and try to kick you out,
so they can breed.
 
Now in social carnivores the
situation is interesting because
they are cases of reproductive
suppression.
And in African hunting dogs,
in hyenas,
in mongooses,
there will usually be,
in social mongooses,
there will be a social group
that forages together,
and usually the dominant female
does all the breeding.
 
The group living brings with it
protection from things like
predators.
 
And if I go back,
these guys are usually all
related in a family,
but they do accept
non-relatives;
the majority will be in a
family but they will accept
non-relatives coming in.
And so kin selection is one of
the things that's going on in
social carnivores,
and it's implying sacrificing
self for relatives.
 
And when we ask what is the
best evidence for this
gene-centered interpretation of
evolution,
we see that wow,
there's some of it from kin
selection,
and that does seem to work some
of the time,
although often there are
alternative explanations.
 
But the really convincing
evidence that it is genes that
are being operated on by natural
selection,
and not individuals,
is the evolutionary theory of
aging and all of the evidence
that now supports it;
which is extensive.
 
And that is that the soma,
which is us,
is sacrificed for the germ
line, which is our offspring
going forward.
 
And here we have lots of
experimental proof that this is
really the case.
 
Okay?
 
It's been done now in possums,
fruit flies,
worms, bacteria.
 
So we have experimental
evolution confirming this idea.
And therefore I would say that
overall this view,
that genes really are what
evolution is operating on,
is pretty well supported.
 
Now that doesn't mean that kin
selection is wrong,
it just means we're more
certain that the evolutionary
theory of aging is correct.
 
I would say that virtually
everyone in behavioral ecology
today accepts that kin selection
is an important thing.
I emphasize these points
because I actually lived through
the period in science when these
were all alternative
explanations and evidence was
accumulating,
and it was clear that things
like the comparison of the
ground squirrels with the
marmots wasn't necessarily
convincing evidence,
because there was the
alternative that they were just
completing the act of
reproduction.
 
Okay?
 
Since then I would say there
have been enough confirmations
of kin selection effects to make
us think that it's very probably
correct.
 
Okay.
 
It does have some problems.
 
There are highly specialized
societies that have fine
division of labor,
extensive cooperation,
and the individuals in them are
no more closely related than are
individuals in simpler
societies.
There has been a tendency to
over-estimate indirect fitness
benefits;
so kin selected fitness
benefits.
 
And that has been done by
including direct descendants of
the pair rather--
which could be,
for example,
parental care--
rather than looking at nieces,
nephews,
aunts, uncles, things like that.
 
The direct fitness benefits
have often been under-estimated.
So there has been more or less
a tendency,
once people learned about kin
selection,
to try to take the world and
fit it into that theoretical
construct,
and in the process people
ignored some simpler
explanations.
So if we want to explain social
living and cooperation,
it might be good to take a look
at some of the alternatives,
because it doesn't look like
kin selection is going to do all
of it.
 
And Tim Clutton-Brock has made
a career out of coming up with
simple alternatives for current
bandwagon explanations,
and this paper here is one of
them.
So let's take a look at social
carnivores.
If the only possibility of
surviving at all is to be in a
group,
and if that group's policed by
a dominant female,
then she has the opportunity of
telling subordinate females that
they've got to stay in the
group,
even if they don't have
offspring, and help her out.
 
Because even if it's going to
take them a long time to grow up
and wait for her to die,
their chances of reproducing,
by doing so,
are greater than if they left
the group.
 
I've been with the meerkats on
the border between South Africa
and Botswana.
 
They live--you saw the Cape
Cobra.
There are also various
eagles--Batteleur Eagles and
Harpy Eagles and things like
that--flying around.
And I would say that the
expected survival time--
not the reproductive success
but just the survival time of a
meerkat that leaves a group--
is on the order probably of
about twenty-four hours;
maybe it might,
a few might make it for a week,
but they're not going to make
it for the months that they
would need to reproduce.
So being in a group is so
important that even if the group
is being policed by a big bully
it pays to stay in it.
And if they do make a mistake
and they get pregnant and they
have offspring,
she'll kill them.
And they're only allowed to
stay in the group if they help.
So what's running this system
basically is a combination of
ecological constraint and
punishment, not kin selection.
Now in a case where you have
tight interactions within a
group,
and the success of everyone in
the group depends upon the
degree of cooperation,
then you can have cooperation
arising for reasons of win-win
kinds of interactions,
even if they're not related,
and if the overall success of
the group can only be improved
by having the rising tide lifts
all boats effect.
Okay?
 
So there is also--this is
something else which is going on
with these social carnivores;
one could conceive of it like
this.
 
Group size increases the
capacity of group members to
catch, produce or defend food.
 
By the way, it also increases
their ability to detect and
repel predators.
 
They can then,
when the group splits up and a
reproductive module is moving
off--it could be five or ten of
them, rather than one or two of
them;
so the offspring group is then
safer.
They do better at raising young.
 
They do better at competing and
defending territories against
other groups.
 
And it has been noticed
that--by the way,
this isn't just meerkats,
this is social carnivores in
general.
 
So individuals that live in
smaller groups have slower
growth rates.
 
They have low survival,
low breeding success.
Small groups frequently become
extinct.
And it's thought that actually
individuals that are living in
this social circumstance might
even advertise to solitary
individuals wandering the
landscape,
"Hey, come and join us,
because if you come and join
us, even though you're not
related to us,
then we will all do
better."
So that gets us into reciprocal
altruism--okay?--and the
conditions under which unrelated
individuals will cooperate with
each other.
 
The basic idea here is win-win
mutualism;
you scratch my back,
I scratch yours.
And so the payoff in equality
is really simple.
If the benefit that I get from
engaging in this behavior is
greater than the cost,
then I'm going to do it,
and if it's the same for you,
then you're going to do it,
and if that is a cooperative
thing then we're both going to
do it and we will get
cooperation.
You'll notice that this is
basically selfish cooperation;
both individuals are gaining.
 
It works best if there are
repeated encounters between the
two agents.
 
You need to have--for
reciprocal altruism you need a
cognitively fairly gifted kind
of species.
Okay?
 
It's got to have good memory.
 
It's got to have individual
recognition.
You need the spatial contiguity
that will result in the repeated
interaction.
 
And the result is long-term
self-interest.
Okay?
 
And often this is coupled with
a disincentive to cheat.
So you saw that with vampire
bats in the movie;
that if they remember that that
individual did not share blood
with them when they needed it,
they won't share back.
And this is very close to the
tit-for-tat strategy in the
Prisoner's Dilemma.
 
So here are vampires again.
 
And you saw the nice overview.
 
So here is the hungry bat and
the satiated bat.
And the hungry bat is more
likely to get fed if she has
cooperated in the past;
so she's getting rewarded for
that behavior.
 
And this is the kind of
cost-benefit analysis that
they're on.
 
This is the amount of
pre-feeding weight that they are
losing over time;
which is interesting.
You can see that they're losing
about oh, fifteen to twenty
percent of their body weight per
day, if they're not eating.
And you can see that the donor
is losing weight and time,
and the recipient is gaining
weight and time.
If it got down to here,
they would starve and die.
So they are really daily kind
of balancing on a nutritional
knife's edge,
and the cooperative behavior is
making a life or death
difference to them.
This is one of the few cases in
which a non-human species has
been observed to engage in
reciprocal altruism.
And I think that if you were to
go into the literature you would
find that some people think that
they actually,
the donor and the recipient,
might be related a bit more
frequently than one had thought.
 
So there may also be a kin
selection element to this.
So helping behavior can be
explained in a number of
different contexts.
 
There's straight out
manipulation,
which benefits the person who
is doing- the individual doing
the manipulating,
and it's bad for the helper.
So, in fact,
you should think of those
social mongoose nurses,
who are sitting there waiting
to reproduce,
as basically paying a cost.
They are getting some indirect
fitness benefit probably,
because they're probably
nursing their nieces.
Okay?
 
So they are getting some
benefit that way.
But they'd be doing a lot
better if they were the dominant
breeding female.
 
In a mutualistic encounter,
as with the vampire bats,
there is a positive benefit for
both in the interaction.
The long-term reciprocal
interaction is a case of
mutualism, but the short-term
reciprocal interaction is not.
The short-term interaction is
very much like the Prisoner's
Dilemma.
 
If those two vampire bats were
only going to encounter each
other once in their lives,
there wouldn't be any incentive
to give the other blood;
the life would not be saved;
and the behavior would not be
selected.
With kin selection the effect
on direct fitness--direct
fitness is direct individual
fitness;
okay, indirect fitness is
fitness through relatives.
In kin selection the
beneficiary gains and the donor
loses.
 
So there is actually a cost in
terms of numbers of children per
lifetime, or numbers of
grandchildren in the kin
selection scenario.
 
With Belding's ground
squirrels, or with marmots,
the cost should be conceived of
as the cost of drawing attention
to oneself when one gives an
alarm call when a predator is
swooping in;
so that in fact the probability
of dying in a predatory attack
is greater if you give an alarm
call, or if you're on guard
behavior.
And, of course,
evolution has acted to increase
the speed and intelligence of
these animals so that they
reduce those costs to a minimum.
 
But that, in principle,
is the source of this minus
sign, right here.
 
So to summarize the
explanations for cooperative
behavior and altruism,
it is now widely accepted that
kin selection does occur,
and it can explain altruistic
sacrifice.
 
A lot of people have seen it as
the biggest deal in evolutionary
biology in the twentieth
century;
at least among people who are
concerned with behavior and the
evolution of intelligence and
things like that.
But the number of cases in
which kin selection has really
been pushed to the limit,
and tested against
alternatives,
is a lot smaller than the
number of cases in which it's
been proposed.
So there was a bandwagon
effect, and people went out and
placed this theory on the world,
and then tried to cram Nature
into it.
 
And the fact that they didn't
doesn't mean that it's false,
it just means that not all of
the cases that were advanced
were truly logically convincing.
 
So the main alternatives to kin
selection are long-term
individual self-interest,
and this would include
punishment and reactions to
punishment.
And we've seen this kind of
thing, both with the vampire
bats and with the social
mongooses and meerkats;
meerkats, by the way,
are also a kind of social
mongoose.
 
And that is really a very
strong direct effect,
and it's quite measurable,
and it's stronger in terms of
effects on reproductive success
than the weaker effects of kin
selection.
 
And then there is win-win
mutualistic cooperation;
and we haven't really gone into
that in detail.
But there are quite a few cases
out there where organisms from
different species,
which by definition are not
related to each other very much
at all,
are creating a mutualistic
interaction which benefits both
of them.
 
And not every symbiosis is that
way, but there are certainly
some cases in which this is a
win-win for both.
Okay.
 
So I'm going to have a review
session tonight,
in here at 7:00,
and I'm going to hold another
review session on Sunday night
at 7:00,
because I know some of you have
conflicts tonight,
for various reasons.
 
And remember these,
especially the May 4^(th)
deadline.
 
That's the one that we can't
bend.
That's the one where you need a
Dean's Excuse if you're going to
go past that point.
 
So it's been fun.
 
Thank you all.
 
See some of you tonight.
 
>
 
