Sexual Violence and Intimidation Go Way Back…To Our Primate Ancestors

MedicalResearch.com Interview with:

Baboon troop: Wikipedia

Baboon troop: Wikipedia

Alice Baniel, PhD
Postdoctoral Research Fellow
Institute for Advanced Study in Toulouse
Manufacture des Tabacs

 MedicalResearch.com: What is the background for this study? What are the main findings?

Response: In many primate societies, sexually receptive females actively solicit
copulations from multiple males, which has long been regarded as the
expression of their free mating preferences. Few studies have
investigated whether this apparent sexual freedom may, in fact, be
constrained by male behaviour.

We tested whether males coerce females
to mate with them using aggression in wild chacma baboons, where males
are much larger and stronger than females. We asked whether male
baboons harass females until they mate with them, punish females after
they have copulated with rivals, or use long-term sexual intimidation
(where male aggression is not immediately followed by mating but
increases the chances that female victims accept matings in the
long-term).

We collected data on sex and aggression across four years
in two large baboon groups living in Namibia.

We found that:

(1) fertile females suffer more aggression from males than pregnant and
lactating females;

(2) aggression from males is a major source of injury for fertile females; and
(3) a male who was more aggressive toward a certain female has better chances to mate with her when she
is close to ovulation.

Males did not seem to use sexual harassment,
since females did not receive higher rates of aggression from males
shortly before mating, nor punishment since females did not received
higher rates of aggression shortly after mating with rival males.
Instead, males appear to attack and chase particular females
repeatedly during the 3-4 weeks preceding their ovulation, to increase
their chances of monopolizing sexual access to them in the days
surrounding ovulation, which can be seen as a form of long-term sexual
intimidation.

MedicalResearch.com: What led you to explore sexual coercion in these baboons? 

Response: Forced copulations have never been described in baboons, so I
specifically wanted to investigate more discreet patterns of coercion.

When I was in the field and observing the monkeys, I often noticed
that males were directing unprovoked attacks or chases toward oestrus
females. They also maintained close proximity and formed a strong
social bond with one particular cycling female, from the beginning of
their cycle until the end. It was within these special male-female
relationships that I observed regular aggression. From that point, the
questions to ask became clearer: I wanted to test whether males use
sexual harassment, punishment or long-term sexual intimidation to
induce females to mate with them.

MedicalResearch.com: What recommendations do you have for future research as a result of this study?

 

Response: What are the most important implications of your findings?

 

 

MedicalResearch.com: Is there anything else you would like to add?

Response: While short-term coercion strategies, such as forced copulations or
sexual harassment, may be well described across mammals because of
their conspicuousness, long-term sexual coercion tactics – where
aggression is temporally decoupled from mating benefits – have been
less studied.

Our results show that this sexual strategy may impact
the long-term reproductive success and survival of the baboons, and
may be widespread across social mammals – especially dimorphic species
where males are larger than females. This study also adds to growing
evidence that males use coercive tactics to constrain female mating
decisions in promiscuous primates, thereby questioning the extent of
sexual freedom left for females in such societies, and suggesting that
sexual intimidation has a long evolutionary history in primates – a
taxonomic group that of course includes humans.

 

 

MedicalResearch.com: How does this add to our understanding of sexual conflict?

 

Response: Sexual violence occurring in the context of long-term male-female
relationships, such as sexual intimidation, might be more common than
we thought in primate and mammal societies. Further research is needed
to examine the taxonomic distribution, and fitness consequences of
sexual coercion, in order to understand its evolutionary importance,
and to identify its main determinants – that is, which characteristics
of the social and mating system drive its evolution. If prevalent in
mammals, sexual intimidation may limit the evolution of female mate
choice as well as influencing the evolution of social and mating
systems, life histories and morphologies. For example, large sex
differences in size or armaments are frequent in mammals. While such
differences are thought to be driven mainly by male-male competition,
sexual coercion might have also played a role.

 

MedicalResearch.com: How surprised were you by the findings?

 

 

Response: I was not surprised by the findings because they correspond to the
impression that I had in the field about male-female relationships.

As mentioned earlier, I observed close bonds between specific male-female
dyads that were characterized both by high levels of affiliation and
of aggression. High-ranking males were often associated with a
particular females for several months – especially when she was
sexually receptive; they maintained close proximity to her, even
outside the period of ovulation, receiving grooming from her, but also
being frequently aggressive to her.

 

 

MedicalResearch.com: What would you like for readers to take away from your work?

 

 

Response: Primates have a rich and complex social life. Males and females can
form bonds over the long-term, which often involve both affiliation
and aggression. In the context of such relationships, males can use
repeated aggression toward particular females to intimidate them and
incite them to mate with them in the future. We already knew that
sexual intimidation occurs in chimpanzees, but this new study, which
shows that it routinely occurs in another primate society, strengthens
the case for a potential evolutionary origin of human sexual
intimidation. Because sexual intimidation – where aggression and
matings are not clustered in time – is discreet, it may easily go
unnoticed. It may therefore be more common than previously appreciated
in mammalian societies, and constrain female sexuality even in some
species where they seem to enjoy relative freedom.
MedicalResearch.com: What’s the next step in this research?

 

 

Response: I would now like to explore the variability of aggression within
male-female dyads. My feeling was that some males were more aggressive
with females than others, and that some females were “happier” than
others with their mate-guarding male. So I would like to understand if
several strategies could coexist among males, i.e. being chosen by
females versus intimidating them.

Second, I would like to address similar questions in humans.

Male-female violence in humans is
prevalent, but remains very variable within and between populations. I
would like to test how variation in socio-sexual factors (e.g. pattern
of residence of woman, number of wives per man, sex ratio within a
society) can explain cross-cultural variation in the frequency of
male-female aggression.

 

MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.

 

Citation:

Baniel et al. Male Violence and Sexual Intimidation in a Wild Primate Society. Current Biology, 2017 DOI: 10.1016/j.cub.2017.06.013

 

 

 

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