Oxytocin, ethnocentrism and evolution (pt. 2)

>> Go here for part 1.

I didn't want to risk making my previous post too long, and I wanted to keep it focused on "hormonal determinism", so I set aside a whole branch of my commentary on the link between the hormone oxytocin and ethnocentrism for another post. The findings I comment on were presented by De Dreu and co-workers in the latest edition of PNAS (see reference below).

So, today I want to talk briefly about bad evolutionary arguments. At the very start of their discussion segment the authors write:

These findings provide evidence for the idea that neurobiological mechanisms in general, and oxytocinergic mechanisms in particular, evolved to sustain and facilitate within-group coordination and cooperation.

There is nothing extraordinary about the idea that there is a neurobiological substrate to human behavior, I hope nobody gets the idea that this is what's in question. But as I tried to point out in my previous post, the probable scenario is a lot more complex than the direct causal link between oxytocin and ethnocentric attitudes that the PNAS article seemed to suggest, and it certainly includes a large societal/cultural component that needs to be addressed. De Dreu does seem to compound his view of oxytocin and ethnocentrism in a recent interview in The Guardian (an interview that is full of "hormonal determinism", it should be noted):

[Oxytocin] may contribute to ethnocentric attitudes but that doesn't mean that people who display ethnocentrism are driven by oxytocin. In the total absence of oxytocin you can still be ethnocentric.

If only this came through in the scientific article!

A helpful commenter also pointed out that any behavioral effects of any particular neurobiological substrate tend to be small. Oxytocin is probably not the be-all-end-all of any of the behaviors it's been linked to.

What's extraordinary about the sentence highlighted in the beginning of this post is that it suggests that a specific oxytocin mechanism that underlies in-group favoritism emerged in evolution and became fixed in the human population. It wasn't enough for the researchers to prove a correlation between the administration of oxytocin and in-group favoritism, in addition they try to make the case that this correlation evolved within an adaptive framework. What does a suggestion such as this really mean?

The authors write in the introduction:

If in-group favoritism and out-group derogation have adaptive value, and sustain in-group functioning, coordination and cooperation, it follows that (i) throughout evolution those individuals who displayed in-group favoritism and out-group derogation and who detected such tendencies in others, were more likely to spread than individuals that lacked these capacities and (ii) the human brain may have evolved to sustain ethnocentrism through yet-unknown neurobiological systems.

De Dreu repeats this thought in the Guardian interview I mentioned above:

Darwin talked about this – primitive societies in which members were co-operative and had a high level of altruism towards one another were more likely to survive. So the idea is, at the biological level, systems that facilitate and sustain group co-operation, such as oxytocin, are more likely to survive.

This shows that their conclusions are based on the assumption that in-group favoritism and possibly in-group-out-group conflict has been adaptive in human evolution. That is, that those individuals who favored their own community and mistrusted or were defensive towards other communities had more reproductive success and thus spread this ethnocentric attitude to subsequent generations until it became a prevalent behavior in more or less the whole human population. This seems like a perfectly reasonable assumption, right? But you can't just stop there! This assumption has to be carried much, much further.

To start, you have to assume that the in-group favoritism or racism as defined is one singular thing which can be isolated, dissected and separated from other human behaviors. From this it follows that this singular behavior actually matches the ancestral constraints, or situations that the human population has faced during evolution. It's possible that our definition of in-group favoritism is flawed on both accounts. You also have to assume that in-group favoritism or racism has a strong genetic component; that you can observe its heritability in the human population. So of course the assumption follows that there must have been an initial variation in the neurobiological regulation of in-group favoritism in the ancestral population of humans, or in other words, that there were several quite recent allelic variants present for selection to work on.

This is quite a handful of assumptions! How many of them are supported by compelling evidence? Possibly the assumption that as a population we have been faced with in-group-out-group conflict with in-group favoritism as an important component, but definitely not any of the others. It's the sort of pop-evolutionary thinking that is usually limited to evolutionary psychology. To be fair though, I don't think you should read the authors' conclusions as a definitive claim that in-group favoritism has been adaptive. It's simply an assumption on which they base their conclusions. But the assumption is flawed and it follows that their conclusions about the role of oxytocin in human evolution have flaws as well. You could just as easily make the case that in-group favoritism has been neutral, or even in some cases disadvantageous, and it wouldn't change the fact that oxytocin seems to be involved in modulating it, at least in some contexts/situations. The same sort of assumptions that I listed above would have to be made and supported by evidence, but in the absence of compelling evidence for either positive selection or neutrality (or even negative selection), all scenarios are equally plausible.


Molecular structure of human oxytocin.

The train of evolutionary arguments is severely lacking in this study, but it doesn't take away from the fact that oxytocin is an awesome hormone and neurotransmitter and the fact that it seems to have some correlation to the behaviors we have defined as in-group favoritism is a fascinating prospect. If we learn to think about these things in the proper way, both with regard to "hormonal determinism" and evolution, and manage to convey the correct view to the general public, there is a wealth of knowledge there to be had! A Wired article from a few days ago talks about other recent findings suggesting that oxytocin is involved in both suspicion and cooperation in a competitive task. Clearly the roles of oxytocin in the brain are connected to social cognition, how we relate to others and how we form relationships, but it's equally clear that we are only starting to dissect its very complex interactions. It's neither "cuddly" nor "dark" in and of itself.

De Dreu CK, Greer LL, Van Kleef GA, Shalvi S, & Handgraaf MJ (2011). Oxytocin promotes human ethnocentrism. Proceedings of the National Academy of Sciences of the United States of America, 108 (4), 1262-6 PMID: 21220339