The Mystery of Our Sexual Evolution – Our two closest living primate relatives, chimpanzees and bonobos, leave scientists puzzled over the origins of human sexual behavior.

Question: You teach a class on sex evolution and human nature.
Do you consider science sexy?   Laurie Santos: Oh yeah. I think science is very sexy.  I
mean, there are a lot of big scientific puzzles when it comes to sexual
reproduction.  You know, why do we choose to have sex?  It would be
much easier just to kind of bud a little clone, boop! It saves lots of
time and energy, waste, and disease and all of these things.  But you
now, many, many animals in the animal kingdom actually put in the time
and energy and risk the disease and you know, all the pains and
heartache to actually sexually reproduce.  So, it’s a big puzzle in the
evolutional biology.  And then when you start looking at the different
ways animals go about sexual reproduction, all the different way they go
about finding mates and you know, strategizing to get mates and
convincing individuals to mate with them, and so on, you know, it’s kind
of just fascinating to see all the strategies that are out there.  And
in many ways, humans are real outliers in this.  So, it’s fun to look at
the techniques that we see across the animal kingdom.  
Question: In what ways are humans outliers when it comes to sex?
  Laurie Santos: Well, humans are a very funny species
when it comes to sexual reproduction.  We’re very weird relative to our
closest living primate relatives, the other apes.  So, we, for the most
part, seem to be a pair-bonded species.  In other words, a male and a
female get together and form this pair bond and kind of cooperatively
rear their young.  There’s nothing really like that in the rest of the
great ape species. In chimpanzees, our closest living relative, you see
lots of multi-male, multi-female reproductive behavior.  Meaning, you
know females are mating with multiple males; males are mating with
multiple females.  But also in chimpanzees, you also see that males and
females just aren’t interested in sex during the period where females
aren’t very reproductive.    So, female chimpanzees advertise
their receptivity, that period when they’re fertile by having this huge
sexual swelling that kind of blows up and males are only interested
during this period.  Somehow humans, unlike our closest living
relatives, have kind of gotten rid of this.  You know, human females of
course, don’t go around advertising with you know, really robust,
blown-up, red, sexual skins when they’re receptive, which is a bit of a
puzzle.  You know, why did we lose this trait just in the last 7 million
years?  You know, these are the kinds of things that hang on for long
periods of time in primate evolution, so the fact that we got rid of
this very quickly is a bit of a puzzle.  So weird kind of weird relative
to other primates regarding our sexual behavior.  Our other
closest… so we have two closest living primate relatives, it’s a tie
between chimpanzees, so common chimpanzees, and their sister species,
bonobos.  And chimpanzees and bonobos greatly differ in their own sexual
behavior.  Bonobos are sort of the “make love and not war” kind of
primate.  They tend to be way less violent and aggressive than
chimpanzees and one of the behaviors that allows them to overcome that
is the fact that they are very sexually oriented.  So, in a lot of the
situations that would cause aggression in chimpanzees, bonobos actually
resort to having sex to kind of diffuse any of the anxiety or stress
about the situation.    So, it’s another puzzle for humans is
that we have one of our closest living relatives is very aggressive,
very warlike, they’re kind of a lot of the stuff that explicitly say we
don’t like about the human species. Our other closest living relative is
very peaceful, you know, very kind of social sexual-oriented has lots
and lots of female bonds.  And there’s a bit of a puzzle in  the field
of what parts of these two guys did the humans get, you know, are we
more like chimpanzees, are we more like bonobos?  Still big puzzles in
the field of primate cognition.Recorded May 21, 2010Interviewed by Andrew Dermont



Leave a Reply

Your email address will not be published. Required fields are marked *