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1. Global Problems of Population Growth: Evolution of Sex and Reproductive Strategies
Poziom:
Temat: Edukacja
Prof: I want to start
today with some stories from the
newspapers: to set a tone.
It was over the last few years.
Tehran: one afternoon Fatima
Eskandari opened the front metal
gate of the shelter she runs for
runaway girls in central Tehran
and was confronted with two men,
armed with knives and rifles.
"Who are you?"
She asked.
"We are the uncles of a
girl named Ranach,
we are told that you are
keeping Ranach,"
and indeed that was true.
Ranach was 16 years old,
and she was inside,
recovering from the bruises
that she suffered at the hands
of these same uncles.
She had run away from home to
escape them.
The uncles had driven from
Sanandaj in the northwest corner
of Iran, hundreds of miles away;
they demanded to see their
niece.
The uncle said she had shamed
the family by leaving home a few
days before.
They had come to behead her.
They were very open about this.
There was no secret.
Staten Island,
New York: A 17-year-old girl
worked as a cashier in a
convenience store.
The store owner said that the
girl was stealing from the
register and he was going to
fire her.
The girl went to her father and
said that the store owner had
groped her.
The father flew into a rage,
grabbed a baseball bat and a
gun, went down to the store,
and killed two people.
Islamabad, Pakistan Zahida
Perveen, 21-years-old was
pregnant in 1998 when her
husband, Mehmood Iqbal,
bound her hands and feet with a
rope.
First he shoved a rod in one of
her eyes, blinding her,
then cut off her nose and ears.
He SUSPECTED her of seeing
another man.
Tuscaloosa, Alabama:
Felicia Scott already had two
sons, but she had an obsessive
desire to have another baby.
She convinced her boyfriend to
help her get one,
so they went out,
shot a pregnant woman,
and cut the full term fetus
from her womb.
Saudi Arabia:
New York Times--A young
woman was raped by seven men.
She pressed charges.
The Saudi Court sentenced HER
to 200 lashes--200 lashes is
almost a lethal dose.
Dominican Republic:
Crucita Medina is 18,
she's been married for a year
in which her husband Jose beat
her constantly.
She had the courage to separate
from him but she met with Jose
after their separation when he
asked her to talk.
He took her to a desolate
street on his motorcycle and
they had an argument.
He grabbed a container he had
filled with - what they call the
devil's acid,
- a mixture of gasoline,
hydrochloric acid,
car battery acid,
urine and other chemicals.
He threw it at Crucida.
The liquid disfigured her
permanently.
It burned her face,
her arms, the right side of her
chest, and a portion of her
legs.
She is still trying to bring
her ex-husband to justice.
Gosarigaon, Bangladesh:
I'm almost done with this.
The village elders met under a
lychee tree to put a value on a
Payara Bigum's grotesquely
ruined face.
A young man had become obsessed
with her;
she was married and he was
turned away.
He took his revenge with
sulfuric acid to erase the
beauty that had once enchanted
him and to empty her life of
happiness.
Her cheeks melted,
her right eye was blinded and
hollowed to a crater.
The husband had to bribe the
prosecutors before they would
even take up the case.
Eventually the perpetrator's
family had to pay a fee of
$3,000.
In one year,
the year I have statistics for,
1999, there are 174 acid
attacks in Bangladesh and those
are the ones that were
officially reported.
Of course, probably the vast
majority of these never get
reported.
The article mentioned a
13-year-old girl who was
attacked as she slept.
Some victims die,
some are forced to marry their
attacker, another was forbidden
to come home until she allowed
her husband to take a second
wife.
Well these stories are
obviously at the extreme of
human behavior,
but the purpose of giving you
all that is to explain that
human sexual behavior has
extremely deep roots,
very emotional,
and very hard to change or
manipulate.
Male/female relationships are
very difficult for humans to
cope with.
I think it shouldn't
particularly surprise you that
human sexuality is not
particularly driven by rational
calculation.
The few stories that I've
pulled out of the newspapers are
just the tip,
clearly just the tip,
of an iceberg,
of a very widespread
phenomenon.
In the long course of human
history across cultures you see
are the--
I gave you everything from
Brooklyn to Bangladesh--
these very similar sorts of
things happen.
Females, through the long
course of history and in most
cultures, where most humans have
lived, females are treated very
badly.
There's a huge amount of
battering.
Battering is the prime human
version of violence,
and females are so
discriminated against that
statistics indicate that there's
something now,
right now, something like a
hundred million missing females.
That these females are either
aborted before they're born,
killed by infanticide,
pretty much as soon as they're
born,
or neglected so that they don't
get the food,
or they don't get the medical
care that their brothers get.
There's a dearth of something
like a hundred million women in
the world today.
These are extreme incidents but
it's an extremely common thing.
One of the purposes of this
course is to try to get you to
understand what is causing all
of this.
From a biological point of view
this abuse of females is
extremely weird.
Males, as you know,
can only reproduce via a female
and so--
and evolution is--the name of
the game is reproducing,
so almost all species--what
kind of female do the males
want?
They want the healthiest,
most well protected,
the best fed female,
and you'll see some examples of
the extremes to which males will
go to provide this so that that
female can produce offspring for
that male and carry on the
evolution game.
In humans, we find that it's
very general that females are
treated atrociously,
and it just doesn't make sense
that human males should keep
many of their females hungry,
sick, and abused.
In childbirth,
if a woman does give birth to a
child they can often be
underweight, sickly,
and it's because the mother is
not in great health.
This is all a biological
disaster the way human males
treat human females and we don't
know--
I mean we do--we have some
idea, why humans do that and the
first part of the course we'll
talk something about that.
That's on the individual level,
and evolution works on an
individual level,
but if you think on a species
level,
missing a hundred million of
your breeders,
that does not sound like a
great tactic for survival of the
species.
I spent some time,
when I started getting
interested in this whole topic,
reading the anthropological
literature,
the sociological literature,
the feminist literature,
and basically I thought all
those explanations were a crock.
I don't think they came close
to an answer.
In my own studies I had to go
back to the very beginning and
understand what sex was really
all about.
I'm going to tell you a few
important things about sex and
reproduction.
The first one is that
reproduction turns out to be
very difficult.
One day I was sitting over in
our botanical garden under a
beautiful big oak--
huge oak tree that they have,
and the ground was just covered
with acorns under this tree,
and I asked one of the forestry
people,
because that's the kind of
things that they know,
I asked them how many acorns
has this tree produced?
They said, well the wind--this
spread is so much and this line,
and you know it's so deep,
and they came up with probably
750,000 acorns a year.
I thought wow,
so I checked the literature and
found that people that collect
these notes for commercial
purposes,
a good oak tree can produce
five hundred pounds of acorns a
year,
and many sources say that an
oak tree produces millions of
acorns in its lifetime.
Wow, a lot of reproduction
right, there's got to be sex
before it.
Then I asked myself,
how many of these million
acorns survive to make a tree
like their parents?
What's the answer?
Basic biology question,
you might know it.
Well, what if each tree on
average,
taking an average of tree made
two acorns,
how many acorns would there
be--how many oak trees would
there be in the--
made two acorns that made
trees--how many oak trees would
there be in the next generation?
Twice as many as now;
what if they only did--and so
that can't continue because then
the Earth would immediately fill
up with oak trees and we'd be
this deep in acorns.
Similarly, if the trees
produced less on average,
less than one,
what will happen to the oak
species?
It goes extinct.
So, over the long time,
on average, each oak tree has
only one acorn that grows up to
be an acorn producing tree
itself.
That's an amazing fact--it puts
out millions of acorns and only
one survives.
Of course this is true not only
for trees but fish,
which spew out--fish
females--huge numbers,
hundreds, tens of thousands,
hundreds of thousands of eggs;
or males of many,
many species that spew out
billions of sperms that,
in a sexual species,
the way mammals are,
two parents on average,
two children.
If two parents for a species
average more than two children,
the world fills up with
squirrels or whatever animal
we're talking about.
If they have less than two over
a long run, they've gone
extinct.
Most species,
in fact, in the history have
gone extinct.
The average of current species
has got to be 1:1 or 2:2
depending on how you count,
but for most species it's less
than that because most species
have gone extinct.
So, the answer is,
it is brutally difficult to
reproduce.
If any given individual in a
species produces a lot of
children,
more than one or two,
depending on how you're
counting,
then that means that some other
individuals are having less,
again, unless the species are
humans,
which are about the only
species that are increasing
continuously over the long time.
As an example,
they now, by this genetic
testing have tested:
how many descendants does
Genghis Khan have?
The answer is 16 million
descendants, this one guy,
so that's an awful lot.
Guess how he did it?
By killing a lot of men and
raping their women.
So he has that many descendants
because an awful lot of men,
all the men he killed,
don't have any descendants.
That's just Genghis Khan,
the Mongol Horde had a lot of
males and I think they spread
their seeds quite widely,
and a lot of males and
conquered people just didn't
survive.
Of course every army in the
world has done--
essentially all--have done a
huge amount of raping,
and it's a wonderful instrument
of gene flow in the human
population.
Because reproduction is
actually so difficult,
species have evolved all kinds
of fantastic mechanisms for
trying to be successful at
reproduction,
so that's Point One.
Point Two is that sex is not
fair.
It's not only difficult but
it's not fair.
Sex goes way back in evolution
and even bacteria do it.
This is--the biologists here
are laughing.
This is the bacteria that are
in your colon and they have sex
in this manner,
and so right now billions of
sexual acts are taking place in
your unspeakable parts,
and this is the way they do it.
Now, in something like this,
actually the exchange of DNA
can be either way and this is--
even though the hairy guy on
the left is producing that long
pilus,
as it's called,
there's more or less equality
of sexuality here.
But when it comes to higher
organisms you get quite a
different story.
You all know the story the
chicken and the egg.
Well the way I tell it is the
poor chicken,
the chicken has to build this
big egg,
it has to eat like crazy,
put all that protein and fat
into the egg which are--
if you're not fed in the
barnyard--which are hard to come
by,
and then once the chicken is
hatched guess who sits--
once the egg comes--out guess
who sits on the egg?
The female.
Guess who protects the young?
The female.
So that's chickens.
You can go all the way up to
humans;
females have to spend nine
months pregnant and then in most
societies and most times females
are the ones that have the
burden of responsibility for the
children.
Meanwhile in all this,
males just produce a little
speck of protoplasm,
insert it into the female,
say, 'bye-bye,
I've had my quickie and I'm
off,' and--
not in all species--but in most
species,
the male has a very minimal
part in reproduction and the
female has this huge burden.
Now why does that come about?
You'd think evolution would
require that females just
wouldn't play this game in
evolution and they would require
a more equal distribution of the
labor.
Well it turns out it
is--starts--as a division of
labor.
The first animals to evolve,
first of anything,
were probably--were almost
certainly in the sea,
and stuck down on the bottom or
floating around and so they
couldn't move.
How do you mate if you can't
get up and find your mate?
Well you just spew out your
sperms into the ocean;
you spew out your eggs into the
ocean, and you hope that they
meet.
Not a very efficient mechanism,
but at that stage,
the male has produced zillions
of sperms, and the female has to
produce zillions of eggs.
If you're an animal and you
have to produce so many of
anything, gametes in this case,
each one is going to be very
tiny.
Two tiny things meet and fuse;
you've still got a tiny thing.
The odds of survival of a tiny
thing are not very great.
Evolution doesn't like that
idea of the male and the female
both spewing out lots and lots
of these tiny gametes.
What happens eventually is that
the two sexes separate,
that the female's job is to
make a big enough egg,
with enough nutrients in it,
so that the organism can
survive,
and the male's job is to go
find that egg.
What do males have--what have
the sperms evolved?
Tails, to take them swimming.
They find--their job is to find
the egg, so there still has to
be lots of those and they have
to expend a lot of energy
swimming.
It's still an equal amount of
investment.
Then the whole animal--once
evolution proceeds,
the whole animal can now get up
and walk over and find a female,
or vice versa,
and now they can copulate or do
some sort of insemination very
close together.
This now does not require
zillions and zillions of sperms.
If you're--if the eggs they
already laid,
like a fish in a nest,
the male just lays the sperms
right on top of the eggs,
and you need some surplus over
the number of eggs but nothing
to compensate for the amount of
energy she's putting into her
eggs.
You start getting an inequality.
As soon as animals can find
each other and mate in a more
spatially enclosed way,
then you start getting
inequality.
Evolution goes down that path
because it's turned out to be a
very,
very effective path,
and what you get is that
females make a few eggs,
her eggs are very expensive,
they are expensive and rare.
Males still make many,
many sperms;
his sperms are plentiful and
cheap.
This is what we call a sexual
dimorphism that males and
females are taking different
evolutionary routes.
Once they take different
evolutionary routes then
different reproductive
strategies come into play for
males and females.
A male, through the first
billion years of evolution has
been producing a lot of sperm,
and now all of sudden he
figures out how to swim over to
a female and he doesn't need all
those sperms but he's still--
evolution is conservative,
it's still--
he's still producing all these
sperms.
What is evolution going to do
with all those sperms?
One thing they can do is--he
can evolve backwards and just
make fewer sperm.
That would save him energy,
it would be good for him a
little bit,
but it wouldn't really get him
an awful lot more children,
which is the name of the
evolution game.
Now what he can do with those
excess sperms,
find another female.
That his limit--there stops
being a limit on the number of
females that he can inseminate
he spreads his sperm to as many
females as he can find.
This dimorphism that sperm are
cheap and plentiful,
while eggs are expensive and
rare, leads to different
strategies of reproduction in
males and females.
It also sets up some odd
situations where,
for instance,
males are expendable.
If one male can fertilize a lot
of females, females don't need a
lot of males around.
For instance,
there's a certain female wasp
that lays its egg in a
caterpillar.
Wasps are one of the major
predators of caterpillars;
they lay the egg in,
the egg hatches and starts
eating up the caterpillar.
All of the eggs that are laid
in a single caterpillar compete
with each other for the food,
that is, the caterpillar.
What happens is evolution has
arranged that the females hatch
first and they eat up all their
brothers except one,
and then that one male can
fertilize all his sisters and
things go on.
The males are expendable in
that case,
and if the females just ignored
them and let them live,
the males would be competing
with the females for food,
the females would grow less big
and healthy,
and they would have less eggs
and evolution doesn't like that
kind of a system.
We'll--all of these things,
if you think,
it's not very difficult to find
human examples of this.
Who goes off to war and gets
killed?
Males, and very often you don't
very any reproductive--any
change in rate;
the females manages to get
inseminated, in humans.
In lots and lots of species,
the number of males is really
not a critical factor in the
amount of reproduction that goes
on.
Males can inseminate many
females,
but females want to worry about
the survival of each egg,
and similarly again,
this is pretty obvious in
humans that a female,
if she gets pregnant,
is going to be spending nine
months pregnant,
and then breast feeds and won't
get pregnant again,
so it's at least a year and
probably at least a year and a
half before that female can get
pregnant again.
We almost always bear only one
child with an occasional twin or
so forth,
so a very low rate of
reproduction where a male
doesn't have any such kind of
limit.
This does not mean that females
are monogamous,
because there are many other
reasons why a female might want
to have many mates.
First of all,
we'll see, she might want to
get resources from many males.
You'll see she sometimes will
not mate with a male unless that
male gives her some resource.
She might want to mate with a
variety of males because she
can't tell which one has the
best genes.
She many want to mate with many
males if her environment is
unpredictable,
and even if she can tell
something about his genes,
she doesn't know what the
environment for her children are
going to be like,
so she wants to shake up the
deck and try--
have a variety of children with
a variety of different genes.
She might want each male to
think that he's the father of
the children so that he
doesn't--that he protects and
doesn't kill the children.
There are species who do that.
There's something called sperm
competition where she may want
to have a whole variety of
different sperms from different
males in her and then the sperms
compete.
Even though this sort of comic
book presentation says,
all males are promiscuous and
males want to go around and have
a lot of sex,
and the females want one,
there's many species with many
reasons why a female may also
want to be promiscuous.
It used to be believed that
many species were in fact
monogamous.
Birds are a very good example:
what you observe is that a male
and a female meet at the
beginning of mating season,
they stay together all mating
season,
she maybe sits on the eggs,
and he brings worms or some
combination thereof,
and people thought,
'Well this is great.
This is monogamy and what
wonderful animals they are.'
Now we can do DNA testing and
it isn't so--apparently--so they
call that now social monogamy
and distinguish it from sexual
monogamy.
While social monogamy is as
we've always believed it to be,
sexual monogamy is almost
nonexistent.
In species--when they
measured--it turns out 10% to
70% of the progeny had been
sired by someone other than what
they called the resident male.
One article I read claimed that
there's only one species where
it is known for sure that they
are 100% sexually monogamous,
and in that case the male and
female physically fuse together,
so neither can go anywhere.
Males have the job of finding
and gaining access to females.
They have basically two
strategies.
One is to let their sperms
compete.
In that case they make just
more and better sperm,
and the sexual system in a
species like that will be
promiscuous,
that the females will mate with
many males,
they'll have a lot of semen in
their vagina,
or spermatheca or sac for this,
and then the sperms will
compete with each other.
Some scientists believe that in
humans also,
we have a variety of sperm,
including killer sperm,
and other kinds of sperm that
go in and facilitate this.
These killer sperm are supposed
to kill sperm that have a
different genotype,
and it's very controversial
about whether this is true or
not.
The data starts when you look
at sperm they have--human
sperm--they have very different
shapes.
And one version is,
well, all these other shapes
are just damaged,
they're just bad,
they're not effective and
there's some evidence for that.
The other story is that,
no, these are doing different
jobs then fertilization,
and it's a hot area of
research.
That's strategy Number One,
to engage in sperm competition,
and you'll see if we get time
that in our related species,
Bonobos, chimps,
our group of species generally
engages in sperm competition.
What you get is very large
testes, so you can determine
this by taking the measure--the
weight of testes--as a fraction
of total body weight.
If it's very large,
you know there's sperm
competition going on.
The other strategy of course is
males can compete with each
other for control of the
females.
This happens of course in
motile--motile animals--
sperm competition is the
original thing where you spew
zillions of sperms and then the
best ones find--
are the ones that find the
females,
but once they're motile,
the males can come into contact
with each other and they can
fight in some way and control a
territory, for instance.
Coral reef fish control
territories in the coral and the
females cruise around,
find a male who's got a good
territory, then come and mate
with them.
Well generally the males will
actually fight with each other
for dominance and then use that
dominance to gain access to
females.
How does this--what are some
examples of how this all works
out?
The females have also two basic
strategies.
One is to get the males to
provide resources other than
sperm, and those resources allow
her to build big healthy eggs.
One of the really cute examples
of this is in the jungle,
protein, nitrogen,
is very, very scarce.
The soils are thin and the
rains wash everything away so
it's really hard to get
nitrogen.
Guess what's a great source of
nitrogen?
Dung.
Any animal takes a dump in the
rain forest, immediately there's
all kinds of--especially insects
that come and are going to
utilize that nitrogen.
It's a really scarce resource.
Beetles have--are ones that are
very good at this and there's a
whole group of beetles called
dung beetles.
What do they do?
They--as soon as they detect
this--by odor probably,
they come in and start rolling
it up into little balls,
because it's much too big for
them.
Let me show you a picture
of--this is a dung beetle,
and what he has done--there's a
big pad--
a big animal pad nearby and
he's cut off with his cutting
claws this big ball,
and that's what he's going to
present to a female.
A whole lot of dung beetles
come in,
they make these balls,
then in the species I'm talking
about they put it on their back
and sort of parade around with
it.
Meanwhile, the females are on
the outside, and they're
watching all this go on and what
males do they choose?
The ones with the biggest balls.
She wants resources and that's
her resource.
Now the most extreme case of
this is in praying mantises.
So a praying mantis is a
beautiful animal,
as you may know,
here's one of them,
but they're very solitary.
They have to actually catch
insects.
They sit on the ends of
branches and--with these
claws--and they wait for an
insect to fly by,
and then they grab it and eat
it.
It's not an easy way to make
your living.
They're poised;
they're very quiet,
and they want to capture a
meal.
They have just a few
milliseconds of something
buzzing by.
Now a male comes up and wants
to mate with this female but
she's ready to eat,
so he's got the problem of
approaching her and not getting
eaten.
In evolution they sometimes get
eaten and that has led to a very
interesting form of reproductive
strategy.
That what you see is that the
male will come on and you can
see--now that's the male on top
and look how much smaller he is
then the female.
In many species the male is
bigger, but he's smaller,
and that's a sign that the
males are not fighting with each
other.
You'll see later that if the
male is bigger that means
they're--almost always means
they're fighting.
She's big because he only has
to make sperm,
she has to make eggs.
Notice he has his head still
on, she has her head on.
That's the way it starts,
and you think that something
normal is going to take place,
when actually in fact,
she reaches around and grabs
him,
she's bigger and stronger than
him,
pulls him off and starts eating
his head.
What then happens is she allows
him to go back,
but now you can see she's still
got her head,
there's no head there.
The way the insect nervous
system is put out;
all the circuits to coordinate
the copulation are down here.
What the head actually does is
inhibit that,
unless it goes and says--well
most situations--
no this isn't right to start
copulating,
but only in the very special
situation where it's a female,
when she eats off his head that
releases those circuits from
inhibition and he copulates her
to completion.
Now--and then she can--when
he's done she can eat the rest
of him.
Now what's really interesting
is--and he doesn't object,
he doesn't try to get away.
What's going on?
The key thing is that this is a
sparse species.
How many of you have seen a
praying mantis?
How many of you have seen a lot
of praying mantis?
One person, you must study them
or something.
They're not hard--they're not
easy to find,
there's not many of them.
If a male is lucky enough to
find a female and get in this
situation,
man he's in heaven,
and it's unlikely if he leaves
her he's going to find another
one.
That's just an unlikely event.
How does he maximize his
reproduction?
Well in my one chance I've got
to have that female produce as
many eggs with my genes in it,
so he wants her to produce a
lot of big,
very healthy eggs and so his
body is the food for her,
including a lot of protein so
that she can make a whole lot of
eggs.
In evolution it's worked out
that males who sacrifice their
bodies to this have more
offspring then males who don't,
so you see the evolution from
him being prey just because he's
prey to it being an actual part
of the whole sexual situation.
The next time someone tells you
that evolution is the survival
of the fittest,
what are you going to tell
them?
Fitness has--survival has
nothing to do with the price of
cheese.
That's only one of the ways.
Now, the next strategy of
females--
the first is to get resources,
the second strategy is for
females to try to find the male
with the best genes and so that
she--
her offspring have good genes
and are very successful.
There's a whole lot of aspects
to this and one is she has to be
able to control which male is
fertilizing her genes.
The more separated the male and
the female, when you spew out
into the ocean eggs and sperm
there's no control whatsoever.
The closer that you come--the
male and the female come to each
other the more control that the
female has.
One of the interesting ways of
looking at this is internal
fertilization,
as in humans.
It is among other things a
strategy for female control.
Internal fertilization and
internal growth of the fetus has
a lot of advantages.
It protects the fetus,
allows the mother to provide
nutrition and waste removal
continuously,
etc.
There are also these aspects to
the female control strategy.
Generally, if a female won't
allow a mating,
it doesn't happen.
If a female doesn't allow it
then rape has to happen.
We'll talk about rape later.
In humans, as you know,
females have a vulva and that's
the Latin word for valve.
She can open it,
she can close it,
and that's the whole idea.
If the female wants to mate she
gets excited and she lubricates,
and the purpose of the
lubrication is to ease
penetration and ease the sexual
act.
Behaviorally she's also--aside
from the beginning she's
receptive, she assumes the
proper posture,
and everything goes just fine.
But if these things--if she
doesn't want to do it and these
things don't happen,
there's no lubrication,
there's no assumption of the
proper posture which is
necessary for internal
fertilization,
then it's very hard for the
male to intermit and probably
sexual intercourse won't happen.
In a real rape,
say among humans,
the vagina does not lubricate,
and that's why there's so much
lacerating and tearing of the
vaginal walls.
That's why it's so dangerous
because it's part of the human
female strategy to control what
males inseminate her is to not
lubricate,
but if she's forced there can
be a lot of damage done to her.
How does a female know which
male has the best genes,
which male to allow to
inseminate her?
She has to either watch a
competition or see the male in
some way,
or know the outcome of some
competition that she doesn't
see,
by say, detecting a male's
position in a status hierarchy.
In some birds,
like flamingos,
there's a beautiful movie of
flamingos doing this which I
don't have time to show,
there can be 100 or so males
can gather together and start
dancing.
It's what's called a lek,
and many of you may have heard
of it or seen it in National
Geographic movies.
The males dance back and forth,
back and forth,
they show their coordination,
they show how perfect their
feathers are,
they show their stamina because
they're doing this for quite a
long time,
and again, the females stand
around on the outside and try to
notice a male who's a good
dancer,
a good strong well coordinated
dancer,
and then she chooses him and
goes off and mates.
By choosing these males that
are not creeping around,
she presumes that she's getting
a male with a good--with good
genes.
Another way that the females
get to choose a good male is by
choosing males who have--
in species where males fight as
part of male strategy then the
females choose the winners.
Males may fight,
and you set up a dominance
hierarchy,
but there's nothing that says
the female has to choose the top
dog,
maybe she wants to choose the
middle dog or a bottom dog,
but in general in species,
females choose the top dog.
They know the result of--in a
variety of ways--the dominance
fights, and the female then
chooses the top dog.
In the male fights,
the winner gets the female,
or maybe gets the whole harem
of females, and the loser may
get absolutely nothing.
Well the females are very happy
to join the winner's harem.
Why is that?
Because once that starts in a
species that means that male has
some genes which allow him to
win these fights.
He's big, he's strong,
he's vicious,
he has sharp teeth,
he's a violent character,
and therefore he is successful
in these battles and the female
wants her young to also--
wants being in this
evolutionary sense of if she
does that she passes on her
genes--
the female wants her offspring
to have these characteristics of
being able to win a fight,
i.e., of being very violent.
She will choose the most
violent male,
the winner of these battles to
father her children because then
they--
then the odds are that they
will also become these big,
strong, violent males.
What happens,
in this case,
is in evolution males may start
fighting and once the females
select the fighter's then both
male and female reproductive
strategy colludes in increasing
the violence a little bit in
every generation.
It's very interesting that
males and females are colluding
in the evolution of male on male
violence.
What else does evolution do?
Well if the males are fighting
each other and reproductive
success depends on winning these
fights, then males will tend to
get larger.
You get a large male,
humans, chimpanzees,
males larger than the female,
and that helps them in the
fights.
It also opens up a second
strategy for reproductive
success--
a second strategy for
reproductive success and that is
that the male is now bigger than
the female and he can start
coercing the female.
He may not have to fight the
males;
he can just coerce,
fight with and coerce this
smaller female.
Then guess what happens?
If that gets into a species
that the males start coercing
the females, what is an
evolutionarily wise female to
do?
She chooses a male who is most
successful at coercing females,
because again,
her children will then inherit
those genes which will allow
them to successfully coerce
females and get more
reproduction and have more
offspring.
Again, we see that not only are
male and female reproductive
strategies cooperating in an
increase in male on male
violence,
they also cooperate in
increasing male on female
violence.
It's really quite an
interesting way of looking at
things and explains--starts to
explain some of this violence
that we see in human
interactions.
Now the great--we belong to the
great ape line of evolution,
and it seems that our line of
evolution seems to specialize in
male on female violence.
Consider rape,
so a lot of political
correctness about use of the
word rape, but I'm going to do
it in a straight biological
sense.
Rape is the coercion of an
unwilling female into
intercourse.
Outside of mammals there are
only a very few species where
rape occurs.
Scorpion flies are one of the
best known examples.
Normal sex occurs when a male
offers a female a dead insect or
other food mass;
she's getting resources from
him.
After she accepts she allows
copulation to proceed,
and it goes smoothly.
Sometimes, however,
sex happens in quite a
different way.
A male without an offering can
ambush the female and she
clearly is trying to escape and
the whole time,
he's got genital claspers to
try to grab onto her,
and she's trying to get away
and push him away,
fly away.
In your reading,
there's a description of this
rape of scorpion flies so I
don't have to go further with
it.
In vertebrates,
rapes occur in several species
of ducks and in mammals there
are only three species where
rape is routine:
elephant seals,
orangutans and humans.
Rape occurs occasionally in
three other mammal species:
chimpanzees,
howler monkeys and gorillas
when they're captive;
it has not been observed in the
wild.
This is really quite striking.
Of the six species,
mammalian species,
in which rape has been
observed, five of those are the
great--are apes.
I'm sorry one is a monkey--of
the five species of primates
where rape's been observed,
four are great apes like us.
Those statistics are way out of
the range of chance.
There is something special
about ape evolution that has led
to this emphasis on violent
relationship between males and
females.
Most likely it is the extreme
unavailability of eggs,
so it's an extremely rare--in
the great apes it's extremely
rare to find a female who has an
egg ready to be fertilized,
why?
Well first, primates take many
years to become sexually mature.
In chimps and humans it's
around 12 to 13 years before a
female can ovulate an egg.
Then primate mothers have these
long gestation periods,
eight months in chimps,
nine months in humans,
and so just counting gestation
and the recovery from
childbirth,
females can have at most one
young a year,
which means one egg available
for fertilization in a whole
year.
Then the females lactate and
you probably know about
lactational amenorrhea that when
a female is lactating and the
baby is sucking on the nipple,
hormones are released and the
female does not lactate--
does not ovulate again.
The average for a chimpanzee is
about another four years in
which the female feeds--
breastfeeds the infant and so
she doesn't come into fertility
again.
Then they can sometimes stay
with their young even longer
time, so the average birth
interval for chimpanzees is five
and a half years.
That means for any female
there's one egg every five and a
half years ready to be
fertilized.
That's Jane Goodall's number,
a Japanese group says it's six
years,
for orangutans it's eight
years, and gorilla females have
a baby about once every ten
years.
There's an extreme dearth of
eggs to get fertilized.
You have a chimp community,
there's say 40,
45-55 individuals,
something like that,
maybe 10 or 12--this is a big
community--
10 or 12 sexually mature males,
about the same number of
females,
non-mature males and females,
and of those then,
given the very long period,
there's probably going to be
one or two females in that whole
year who are going to be fertile
and in estrus and ready to get
fertilized.
These males spend the whole
year, in terms of their
reproductive evolution,
spend the whole year setting
themselves up to have that one--
to inseminate that one egg
that's available in that whole
year.
You can imagine there's going
to be a huge amount of
competition, a huge amount of
violence among the males.
As we've seen that male/male
violence then spills over into
male/female violence.
Within this group--we belong to
an order called primates,
as you know,
and within this group monkeys
are fairly distant relatives but
the rest of the great apes are
fairly close.
You can see there are a lot of
similarities,
these are some jokes about the
singles bar, even in biology
there's some sense of humor
still left.
Now, this is another professor
at Yale and I always ask
students--you have too many
advisees--so I asked them
wouldn't you rather go to this
guy?
He looks very fatherly and kind
and everything.
Well that's an orangutan.
Of the great apes,
it's as far a distance from
humans as--
the most distant species and
yet looks pretty much--
you can empathize with that as
almost a human being.
It doesn't take a lot of
evolution to go between these
two.
There are five species of great
apes.
That's a young guy.
This is a time scale,
about 15 million years ago
there was one line of evolution
coming up from a long time ago
and the first event was that
orangutans split off the tree,
that the tree split and one
branch became orangutans.
Then about ten million years
ago another--there was another
split and gorillas went off,
a group went off and became
gorillas.
Then about six million years
ago another group came off and
they evolved into humans.
The most recent split is about
two million years ago and gave
two species, very similar
species: chimpanzees and
Bonobos.
The farther distant the split
is the more there's been time to
evolve differently,
so an orangutan who as that
nice guy,
is very distant from the other
species.
That's our family tree and the
difference--this is a fairly
recent split here.
The genetic difference between
these three species,
between any pair of those three
species, is about 1.5%.
If you draw out the DNA
sequence for a chimpanzee and a
human and look at the base
pairs,
out of every hundred,
98 or 99 will be identical and
one or two will be different.
We're extremely similar
genetically.
Now, what does this difference
mean?
1.5% or 2%, we don't have the
foggiest idea of what it means.
Obviously, you can look at a
chimpanzee and say,
hey it isn't human,
and their behavior is different
and they can't speak,
and all kinds of things,
but genetically there's not
that big of a difference.
I wouldn't draw any particular
conclusions from the genetics
yet.
This is a rapidly evolving
field and we're going to learn
an awful lot very quickly,
and one doesn't know what the
conclusions are going to turn
out to be.
One thing which may be solid is
that if you look between a man--
females have two X chromosomes
and males have an X and Y
chromosome,
so you can ask,
well what is the genetic
distance between a human male
and a human female?
Guess what, 1.5%.
Whatever you think of the
difference,
genetic distance of those
species, you pretty much at this
current stage of our knowledge
have to think the same as the
genetic difference between a
human male and a human female.
That's just for your thinking.
Each of the great ape species
has evolved a different social
system to organize reproduction.
All but one have an awful lot
of violence associated with it.
Orangutans are the least social
of apes.
The males and females generally
stay apart, and the mother and a
child are the only stable social
unit.
The offspring stay with the
mother until adolescence,
very much like the chimpanzee
story and like the human story.
It's about ten years before the
young separates.
For most of the eight years
between births,
the mother has no interest in
males at all,
no interest in sex at all;
she doesn't really come very
close to them.
There are two kinds of
orangutan males.
There's a large one and a small
one.
The big males are about 200
pounds, the females and the
small males are less than half
that size, about 90 pounds.
The small male develops
normally up to adolescence and
then just stops developing
further.
Doesn't develop the
characteristics of the full
male, doesn't grow a beard,
crests of the hair,
throat pouches,
etc.
They remain looking like
adolescents.
But, they are completely
fertile, have a normal
complement of testosterone,
they're sexually totally
capable, and they can stay in
this adolescent stage for up to
18 years,
maybe longer but that's the
most that anyone has observed
them.
They probably don't grow into a
big male until the dominant male
in the region has died or is too
weak to defend himself.
The females always want
to--When they have a choice they
always want to mate with the big
males because the big males are
more successful,
and it's the old story that
females mate with males of a
type that are already successful
because that is good for the
genes that her children get.
In the mating between a female
and a big male,
sex is very relaxed,
it takes on a languorous
quality, an erotic quality,
there's not a great rush.
Matings can begin with oral or
manual manipulation of the
partner's genitalia,
and it can be initiated by
either the male or by the
female,
and when they finally do engage
in intercourse they do it often
face to face,
missionary style,
and it takes about as long as
it takes humans:
an average of 11 minutes and up
to a half an hour,
just in case you want to
compare.
Now these big males are
ponderous,
they can't move fast,
whereas, the females are lithe
and they can go pretty fast,
so you know the female is
choosing the male,
because if she didn't want him,
she could be gone and there's
no way that he could catch her.
What about the small males?
They are not attractive to
females but they have one
advantage, they're small and
they're fast,
and they can run fast and they
can catch females.
That's what mother evolution
has done.
They try to catch and rape the
females.
The females are usually,
as I said,
alone with their young and if
they're found by a single--
by one of these small males
they're chased and sometimes
they get caught,
and then the females show fear
and they struggle to escape,
and the males sometimes strike
them or bite them,
and the females scream and the
young--
they're dependent--the young
scream,
the females bite back,
they hit, they pull the hair of
the males while the copulation
is going on and that lasts --
not more than ten minutes.
How common is this?
Different--orangutans are very
hard to see.
They live in a part of Borneo
that's hard to get to and
they're very hard to see.
There are different studies
coming to different conclusions.
One ethologist found that about
a third, 1/3 of orangutan
copulations involve some degree
of forcing of the female by the
male.
Japanese observers reported
that 88% of the copulations were
rapes and that these were of the
severe kind.
A Dutch observer judged half
the copulations to be rape,
so these are not rare events.
They're a standard part of the
orangutan sexual strategy.
There's a lot of examples where
orangutans are close enough to
humans that apparently a lot of
those same sexual signals are
passing.
A woman primatologist who ran
primatology research in Borneo
talked about an orangutan who
had lived with humans for a lot
of his life,
so he was very acculturated to
humans.
One day apparently he raped one
of the female cooks,
the orangutan,
the male orangutan,
raped one of the human female
cooks at the camp.
Apparently it was a complete
rape with penetration and
everything.
As you know,
rape is a big embarrassment for
the female,
as well as the male,
but in this case,
and this was in Indonesia,
the husband,
very unusually,
took it quite easily.
The husband said that since the
rapist was not human,
the rape should not provoke
shame or rage.
He said, "Why should my
wife will or I be concerned;
it wasn't a man."
There are all kinds of stories
that I don't have time to tell
you about.
Okay, now why doesn't evolution
just keep the big males and the
females together?
Probably food density because
food is hard to get and
individuals have to forage alone
to find enough food;
if they foraged in pairs what
they found would not be enough
for two of them.
Now gorillas live in a region,
and have an ecology that they
have more food available to
them,
so they live in somewhat larger
groups and in gorillas the
females stick close to the male.
Each male, big silverback male
can have a harem of say three to
four females.
In these harems,
they spend most of their time
just the few of them together.
They're quiet;
they're relaxed;
they're affectionate with each
other;
the troop is stable with the
one silverback,
the three or four females and
whatever young they have.
Very little aggressiveness
of--between the males and the
females, or female to female,
just hardly happens.
But, as I said before,
if one male is controlling
three to four females that means
there's two to three males that
don't have any mates whatsoever.
What is evolution going to do
with those bachelor males?
Again, it isn't nice.
The males--so the gorillas
travel through the jungle,
resting some,
eating some,
they eat fruits,
they eat roots,
they eat shoots.
These bachelor males follow the
troop on the uphill side and
just wait until the silverback
is not watching.
Then they charge down,
they can make a fair amount of
noise,
so often the silverback notices
and goes over and beats the hell
out of the guy and he retreats
again.
Every so often he's successful;
the male is with another female
or off--never very far away,
but a little away.
He goes down and what does he
do?
He charges downhill,
so he gets up a lot of speed,
he charges right at a female
with a young,
he grabs the young immediately
smashes it on the ground and
kills it;
runs away and doesn't try to do
anything, but just kills the
young of the female.
Now what does the female do?
The female's are-- these are
very smart, they're great apes
so they're very smart;
they recognize each other as
individuals;
they have long memories,
so you would expect that this
female would remember this male
the rest of her life and fear
him, hate him,
avoid him.
In fact the opposite happens.
What happens is the female
within a few days generally
leaves the silverback that was
supposed to be guarding her and
goes with the single male and
they go off and have a
consortship.
What the message that the male
is delivering to the female is,
'Look you've put a huge
investment into this infant and
now it's wasted.
That guy can't protect you.
He has too many females;
he's too old,
he's too big and slow,
he can't protect you.
I can--you can stay with him,
get pregnant again and I'm
going to come down and kill your
next baby too,
so if you want to reproduce you
come off with me.'
Of course none of this is
verbal, this is an evolutionary
story, I hope you understand
that.
They're not mentating this
stuff that I'm saying.
What you notice is in a few
days this female leaves and goes
with the male that has just
killed her young and starts
reproducing with that one.
That may be stable and last a
long time, or another male may
come by and in a few months
separate him--separate them.
Again, these are not isolated
incidents.
Diane Fossey had data on about
50 infants;
38% of them died before they
were three, and 37% of those
were from infanticide.
About one infant in seven dies
from infanticide,
and each of the female gorillas
she studied had at least one
infant that was killed by
infanticide.
In the gorillas,
the females are trapped in this
vortex of male initiated
violence.
At any moment a male may come
crashing through the forest and
kill her young,
and the best way for her to
prevent this is to go off with
that male.
She needs protection,
she lives in a world of baby
killers and she needs some
protection from them.
Chimpanzees--so we're going
down the list of species,
and we won't get time to
finish, but chimpanzees have yet
another solution to this primate
reproductive problem of very,
very scarce eggs.
Unlike orangutans and gorillas,
the males are not solitary,
but related males spend their
lifetime together as a
community.
Chimps live in groups of about
40 individuals,
with a dozen or so adult males,
and a similar number of adult
females.
As with the orangutans,
the chimp females spend most of
their time alone with their
young,
and they're not separated from
their young until the young are
several years old,
really into adolescence.
First they hold them,
they're not physically
separated for several years,
and then for several years
they're not out of sight,
and then for several more years
they're not out of voice
contact,
so it's really very,
very tight bonding between
mother and children.
The males defend a rather large
territory,
numbers of square kilometers,
in which they range and which
the females range,
and the males spend their time
searching for food,
patrolling the borders,
the territory,
and they're often with other
males.
This patrolling is often--is a
bunch of males together and they
go around checking on the
females to see which ones have
come into estrus or if any have
come into estrus.
As I mentioned,
the females come into estrus
only about once every six years
after their last young was born.
They have a 35-day cycle,
very similar to humans,
and are sexually receptive for
about 15 of these days in each
of their monthly cycles.
Her fertility increases during
these 15 days and she's most
fertile the last two or three
days of this receptive period.
The females do an interesting
thing, have you ever been to a
zoo and looked at chimpanzee
females?
What do you see?
Big red rump if they're fertile.
It looks rather disgusting to
humans,
and I've been looking for a
picture of it,
and amazingly it's such a
striking thing,
I cannot find a really good
picture of this.
You go to a zoo it's very,
very obvious they--they're
called ano-genital swelling.
They advertise their estrus.
Oppositely to humans;
humans keep their estrus secret;
neither the male nor the female
knows whether they're in estrus.
Chimpanzees advertise it,
everybody knows.
Now why do they do that?
Well what happens is when a
female comes into estrus,
the males have been waiting all
year for this,
the males congregate together
and what do the males start
doing?
Competing for the female.
They're fighting,
the dominant male arrives,
and it's clear whose dominant,
so the females advertise as a
way of inciting male violence.
That they want to be able to
choose the dominant male,
the ones that are in great
fighting form,
so they say,
'Hey I'm in estrus,
all you guys come and fight,
and I'm going to sit there and
choose the best of you,' which
in this case means the most
violent of you.
Unfortunately,
in this situation,
all these males are not only
fighting with each other but
they're trying to get at the
females,
so the females are herded about.
They have to run around to
escape the clashes with the
males.
They regularly receive quite a
lot of wounds when they're
chased they try to climb up
trees to escape this and
sometimes they fall out of
trees,
and they have their young with
them,
and the young sometimes cling
to them and then if they--
the mothers fall, the kids fall.
It's a very,
very dangerous unpleasant time.
The violence is so great that
when a male approaches a female,
she doesn't know whether he's
coming to be--
to try to mate with her or to
be violent toward her because as
you'll read in the reading how
the males have a long history of
being violent to the females.
It's a way of cowing them so
that when they're in this melee,
when they're in estrus and the
male approaches them,
they don't resist.
If they do try to resist he
does a lot of violence on them.
The male has to--when the male
comes and wants to mate with
female,
he has to signal to her don't
run away,
I'm not going to try to beat
you up and he has--
this is--orangutans,
gorilla, chimpanzee with her
young.
This is the--this male is
inspecting the female,
not only is there a red rump
but there's odors,
chemicals, and he's trying to
see what the status of her cycle
is,
and this is a male
displaying--letting a female
know that this is a sexual
engagement.
Humans have been known to do
the same thing.
This is a picture from ,
the same sort of advertising,
with pretty much the same
message, and here's an
incredible photograph.
I don't know should I leave
that on the board for you?
I get in trouble leaving things
like that on the--up for too
long.
Okay, now, so in this great
melee, this great violent melee,
there's all the males there
trying to get at this female.
If a male does--let's say that
alpha male is off fighting with
someone else and the female is
alone for a minute,
the male--any male that's
around rushes in.
He's not going to have a lot of
time before the other males
notice what's going on and rush
into separate them,
because they're all competing
to inseminate that egg.
The males have a very short
time in which to complete the
copulation, and ejaculation
occurs after just 15 seconds,
with only 8.8 pelvic thrusts.
I think those are very
important numbers you should
know, but the females make up in
quantity what they don't get in
quality.
They appear--and there's a
story behind this,
but they appear to be quite
promiscuous in their sex
partners.
In the community followed by
Jane Goodall,
in each estrus cycle,
each female had at least one
bout of intercourse with every
male,
so all the males are getting
some chance at having
intercourse.
They average six encounters a
day.
Don't get excited,
it's still only a minute and a
half at their rate,
and in each monthly sexual
cycle they have about 100 or so
bouts of intercourse,
so there's a lot of sexuality.
Do females have orgasms?
Not known;
there are debates about it,
but not known.
All right, I guess our time is
running out.
We will continue on Thursday
and I'll set up sections in
between, and any questions?
I stay after every lecture for
as long as necessary if people
want to come down and ask
questions.
