Monday, November 17, 2014

Mean male chimps produce more offspring-implications for humans?

A study came out about chimpanzees recently that has received a lot of attention. You may have seen a headline on sites such as ScienceDaily, Smithsonian, and other websites stating that male chimps that bully females are more likely to reproduce. Specifically, researchers looked at 16 years worth of data from Gombe National Park in Tanzania (Gombe is where Jane Goodall first studied chimps). They found that males that were sexually coercive, or those or threatened or used force against females,  fathered more young than males that were less violent towards females. Male chimpanzees that acted violently towards females year-round (as opposed to just when females were receptive, or ready to mate,) were more successful. Those males that increased aggressive behavior towards females only when females were receptive did not have any advantage in fathering offspring.

Our closest genetic relative, the chimpanzee
Now, this study is a great example of how results and interpretations differ. It also presents the perfect opportunity to talk about how science reporters for the general public often misunderstand or sensationalize scientific research. News sites will get more people to click on their site if they use certain words and only report some facts to create a more interesting (although probably misleading) story.

The fact is, there are many ways to interpret this study, and the close genetic relationship between chimpanzees and humans means that of course we're all going to ask, what does this mean for humans?

Well, with sixteen years of data, there's certainly enough evidence to say that bullying females provides an advantage for chimpanzees at Gombe. However, how do we not know that these bullying males are aggressive with all chimpanzees, males and females and that aggression in general is the trait increasing their sexual advantage? Maybe this is the case or maybe not. My point here is simply that chimpanzees and complex and their reproduction and mating rituals are also complex.

Chimpanzee and offspring Photo credit: Neil McIntosh
It's not as simple as saying, "Oh, well if chimps that are mean towards females are more successful reproductively, the same must be true for humans." Many factors go into chimpanzee reproduction and many factors go into human reproduction. As similar as we are, we are not the same. Study author Joseph Feldman even states on ScienceDaily, "The glaring difference between chimpanzee and human mating behavior is that in chimpanzees females mate promiscuously with most male group mates during most cycles, while human females do not. Thus, the system that favors male coercion in chimpanzees is not present in humans to favor this behavior." The authors also point out a fact that all of the articles I've read so far seem to overlook: studies of chimpanzees at other sites have not found a link between sexually coercive males and the number of offspring they father. Thus, we need to remember that these results are specific to the chimpanzees studied at this site and not all chimpanzees in Africa.

The take home messages are; 1) be careful when reading about science from sources other than the original scientists and 2) with animals and biology especially, remember that simple studies are needed for us to ask answerable questions, but that the reality may be very complex.

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