All walk and no trouser

A study shortly to be published in the Archives of Sexual Behaviour reports that the menstrual cycle has an effect on women’s walking style and its attractiveness to men, but has also provoked speculation that highlights the worst in evolutionary psychology story-telling.

The study found that women’s walking style differed during the menstrual cycle, but that men rated it as most attractive when they were least fertile.

This contrasts with several previous studies have found that women dress, act and are perceived as most attractive during their most fertile time of the month.

Some researchers suggest that we’ve evolved so women subtly advertise their fertility to potential mates, perhaps, quite reasonably, as this happens in far more obvious ways almost uniformly throughout the animal kingdom.

So you might think that something to consider is that this finding is evidence against this idea, or that maybe the link with walking style is just a ‘side-effect’.

For example, estrogen affects dopamine function in the striatum, part of key action pathways in the brain, and the menstrual cycle is linked to changes in neuromuscular coordination. It could be that evolution has selected for the behaviour via these mechanisms, but it could also be that they have no evolutionary significance.

However, the alternative is barely considered in the paper or in the press reports. This from New Scientist:

However, Provost and her colleagues say there is in fact no contradiction between this research and other studies, as they are investigating two different kinds of signal. The previous research investigating men’s response to fertile women focused on signals such as smells and facial expressions, which can only be detected at close range. That makes evolutionary sense, as it would benefit a woman to advertise her fertility to a man that she has decided is worth having children with and has therefore allowed to get close to her.

In contrast, men can pick up on the attractiveness of a woman’s walk from long distance, and it can therefore act as an unwitting signal to less appealing males who she might not want to choose. So the advantage of having a less sexy walk around the time of ovulation becomes clear: it allows a woman to hide her fertile period from undesirable men who might take advantage of her at that time.

As an explanation, I actually quite like it, but there’s little consideration of the ‘side-effect’ idea, or even the contradictory evidence. For example, it goes against research which suggests that women dress more attractively during their most fertile time.

Evolutionary psychology is sometimes criticised for creating ‘just so stories‘ – unverifiable explanations that weave a story about how the data suggests that evolution has selected for a particular cognitive or behavioural difference.

It’s true to say that this accusation is levelled at evolutionary psychology more than is warranted. It does make testable predictions and all science involves some story telling to some degree.

Nevertheless, evolutionary psychology researchers would do well to show that they are considering the alternative explanation – that some behaviours might be associated with sex or fertility while having no influence on survival, the chance of mating, or passing on certain genes.

At this point I normally castigate the media for picking up on the sexy speculations and not the debate, but unfortunately, in this case, the scientific paper seems to make the same mistake.

Link to abstract of study.
Link to media reporting.

One Comment

  1. Posted November 11, 2007 at 3:38 pm | Permalink

    I think the authors have also misrepresented their own findings by playing down the fact that men actually did not differ in the attractiveness they assigned to women in the follicular and luteal phases.
    Instead they constructed a discriminant function and used it to assign how ‘fertile’ a woman’s walk was – this is obviously completely unrelated to the woman’s actual underlying ovulatory status – and found that the assigned attractiveness of gaits varied by their discriminant function scores, with scores classifying women as luteal being ranked as more attractive.


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