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Research Article

Wild Chimpanzees Exchange Meat for Sex on a Long-Term Basis

  • Cristina M. Gomes mail,

    gomes@eva.mpg.de

    Affiliation: Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany

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  • Christophe Boesch

    Affiliation: Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany

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  • Published: April 08, 2009
  • DOI: 10.1371/journal.pone.0005116

Reader Comments (4)

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Cause Or Effect?

Posted by heenan73 on 08 Apr 2009 at 09:30 GMT

Researchers need to be wary of assuming cause and effect when observing an association.

In this case, the assumption is that the chimps are 'paying for sex', while an alternative conclusion is equally supported by the reported evidence.

It may be that the chimps who failed to get regular sex had learned to be selfish about their food; it may even be a matriarchal control mechanism; rewarding successful hunters with sex.

All the study shows for sure is an association. The selected conclusion makes fine headlines, but may not be the whole truth.

No competing interests declared.

RE: Cause Or Effect?

cristinagomes replied to heenan73 on 09 Apr 2009 at 10:13 GMT

Thank you for your comment and for your interest in our work.

I fully agree with your comment on cause/consequence. However, we were very cautious as to not assume cause consequence and we never did. Females could be copulating more with males to get meat and males could be giving meat to females to increase their copulation frequency. However, we never suggest one possibility or the other and in fact its not necessary for one behaviour to precede the other. We simply say that there's a correlation between these two variables and that this indicates that by exchanging meat for sex, males increase their mating success and females increase their caloric intake. We never state in the paper that chimps are 'paying for sex'.
In an exchange, it doesn't necessarily matter who gives what first and there's not necessarily such an order of events.

Although its possible that chimps who failed to get regular sex learned to be selfish about their food and this possibility was never excluded in our paper, a mechanism of rewarding successful hunters is a completely different issue. Why would a female take it upon herself to reward a successful hunter by copulating with him, unless she is getting a direct benefit? This doesn't really make evolutionary sense unless its accompanied by other controls. Or else, how would such a mechanism evolve?

I hope I have addressed your concern and I'd be happy to hear your thoughts on this matter.

No competing interests declared.