Buller and the origin of promiscuity among modern humans

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Buller and the origin of promiscuity among modern humans

Post by gruesomehound » Sun Sep 13, 2009 4:30 pm

Hello to all of you, I write this post because I would like to know your opinion about one relatively recent article of David Buller where he claims (among other things) that promiscuous behaviours among modern humans have not been shaped during our specific evolutionary history but stem directly from our common ancestor with chimps and bonobos.

First of all, I must say that I consider evolutionary psychology to be a very speculative enterprise, since there is really a dearth of data about the psychology of our ancestors/cousins over the past millions of years. So, at the beginning, I really appreciated his paper, where he exposed what he calls four common fallacies of evolutionary psychology.

However, Buller himself seems to grant the very same kind of flawed reasoning he has just denounced, in that he affirms at page 4 of the article, that our inclination toward promiscuous behaviour can almost certainly be traced back to our last common ancestor with chimps and bonobos ( let's call it CA for short) , and was already present long before the beginning of the Pleistocene.

His claims are the following:

http://www.scientificamerican.com/artic ... ies&page=4

“If we recognize that aspects of our psychology are holdovers of prehuman evolutionary history, we get a very different picture. Indeed, because our closest relatives, the chimpanzee and bonobo, are highly promiscuous species, our lineage likely embarked on the uniquely human leg of its evolutionary journey with a mechanism of lust designed to promote promiscuous mating. Psychological characteristics that subsequently emerged during human evolutionary history were built atop that foundation. And we know that some emotional systems subsequently evolved to promote the pair bonding that is ubiquitous among human cultures but absent in our closest primate relatives. We have no reason, however, to think that mechanisms of lust and pair bonding evolved together as parts of an integrated mating strategy. Indeed, they likely evolved as separate systems, at diverse points in our lineage’s evolutionary history, in response to different adaptive demands, to serve distinct purposes. If this alternative interpretation of human mating psychology is correct, we are not “of one mind” about our sexual relationships. Rather, we possess competing psychological urges. We are pushed toward promiscuity by evolutionarily ancient mechanisms of lust and toward long-term pair bonds by more recently evolved emotional systems. Rather than being driven by an integrated Pleistocene psychology that unconsciously calculates which urge to pursue when, we are torn by independently evolved emotional mechanisms.”

According to him, it is almost sure that CA was promiscuous because we see this behaviour both among chimpanzees and bonobos, and clear inclinations/temptations among present human beings.

Now, I recognize this sounds like a plausible scenario, but I am not quite convinced it is the only one possible, for there remains some alternatives which have not been refuted to my mind.

Let us consider violence. Bonobos and chimps are known to radically differ with respect to that, since the first ones like to use sex as a mean of reconciliation, whereas the second ones do not hesitate to employ violent methods to deal with conflicts.

Among human beings, it seems to me that sex is a rather seldom solution for coping with conflicts (except perhaps in the case of an already existing relationship, whatever the number of partners) and that while violence is used pretty often (we have a clear inclination towards it) , it is not the only solution and mankind was able over the centuries to develop various more peaceful ways. Now, was CA violent like chimps (and potentially humans) or was it rather peacemaking like bonobos, or a compromise between both ?

My short answer would be that all three cases are possible, and there is no way to tell which one is true, for six millions of years are largely sufficient to explain any kind of behavioural shift among the three species, whatever the starting point might have been.

I think a similar type of reasoning can be applied to the case of promiscuity: was CA promiscuous? Does promiscuity among modern humans directly stem from CA ?

I am not quite persuaded these are the only possibilities.

For let us consider for instance he lived in an environment such that the forming of stable bonds over rather long periods of time would have been adaptive for him according to his psychology.

Since the data concerning him are at best really scarce (in fact, we are not able to make the difference between him and many other side branches of our evolutionary tree) , this hypothesis has clearly not been disproven by archeology/paleontology.

Now, I believe it can also accommodate the data of the modern world, in that the evolution of promiscuity could have occurred separately for chimps/bonobos human or perhaps even for each of them.

Over the last decades, evolutionary biologists have been growingly confronted with the phenomenon of convergence, that is the development and appearance of similar organs in completely unrelated species. This is for instance the case for eyes among vertebrates and invertebrates, the evolution of fly among insects, birds and mammals (bats) and so on and so forth. So, the presence of a common characteristic among different species can no more be used to deduce that the characteristic in question was present among their common ancestor, since it could as well have undergone a parallel/convergent evolution.

In the case of promiscuity, it is quite possible that this behaviour has undergone three different evolutionary histories for our three species, this would be in fact consistent with them having undoubtedly developed three different attitudes with regard to violence/reconciliation.

I think therefore that Buller has failed to prove that promiscuity is a straightforward holdover from CA, so that our promiscuous behaviours have not been shaped by the lifestyle of our ancestors during the Pleistocene.

In effect, the scenario of Pinker/Buss and many other folks that promiscuity among modern humans has specifically evolved during our own Pleistocene story, after the separation with chimps and bonobos, has not been refuted and remains a possible explanation.

I am not saying here that Buller's account of human promiscuity (we have directly inherited it from CA) is false, but rather that he has failed to prove it to be true, in that other accounts like the one I have just proposed remain possible.

For fruitful works and dialogues, I think it is important for researchers in EP (in the broad sense, this would include Buller) to be liberated from two illusory beliefs :

1) the conviction we can use the scientific method to determine unequivocally and with almost certainty our evolutionary story: even history (which I would loosely define, just for the sake of this discussion, as the study of mankind's evolution since the invention of writing ) is quite limited with respect to that: in many cases, the discoveries of written artefacts and archaeological remains are quite scarce and ambiguous, so that many plausible explanations may be offered and account equally well for the same data. Using mathematical language, this means that the models are under-determined, in that the available data are much less numerous than the parameters which are necessary to unequivocally determine them. If this problem is even a concern for historians, how much is it the case for the study of our own evolution, where behaviours don't fossilize (to quote Jerry Coyne ), fossils are scarce and could also belong to side branches, and many complex phenomenon (like convergent evolution, fast changing environments and so forth.) are taking place.

In such a situation, researchers would be well advised to recognize that a plurality of perspectives/theories can account for the same data, and popular journalists should cease presenting some speculative theories to the public as if these were facts. In the case of promiscuity, I believe that several speculations are equally plausible.

2) the conviction that we can examine the data and form the theories accounting for them in a fully objective way: we all have our own social, moral and political background which underlies our opinion of what ought to be the case, so that there will be an inexorable bias in nearly each of us to find data sustaining our views. Hardcore Evolutionary Psychologists with their modular understanding of human nature are as well concerned as "blank slate" theorists.

I have not written this post to demolish the field of EP, but rather to encourage current researchers and those interested in to be more sceptical and consistent.

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