Digit length and propensity to exercise

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Yan, Malisch, Hannon, Hurd, and Garland have an interesting (though ultimately more suggestive than conclusive) paper in PLoS (link goes to abstract but PLoS is free so you can read the whole article). The background here is that 2D:4D, the ratio of index finger to ring finger length, is lower in male humans than female humans. It appears that this is correlated to prenatal androgen exposure as well as to gender: female fraternal twins whose co-twin was male tend to have lower 2D:4D than those whose co-twin was female. It also turns out that low 2D:4D ratio in humans correlates with a bunch of measures of what you'd think of as masculinity: aggression, competitiveness, etc. Interestingly, the opposite is true of mice: higher 2D:HDs correlate with higher levels of aggression and physical activity. Also, in mice females exhibit higher exercise levels than males. What YMHH&G have shown is that in mouse lines bred for increased propensity to run on treadmills: 2D:4D is higher than in un-selected control lines.

It's hard to know what to make of this general set of results and the authors grapple with it a bit (the selected mice are feminized, masculinized,...), but don't have any clear answers, though they suggest that it's more complicated than either. In any case, it's interesting that (a) you can actually select for propensity to exercise, at least in mice, and (b) that that somehow seems to be linked to a bunch of other biochemically significant markers.

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As I read it, "propensity to exercise" is just a proxy for general physical activity level. That is, very physically active mice will tend to hop on the exercise wheel a lot, because that's a way of being physically active while in a cage. Or have I misread it?

This isn't terribly surprising. 2D:4D has been known to be a predictor of athletic performance for several years. It turns out there's even a good correlation when looking at 1st and 2nd team professional football players, which is really interesting because the difference in ability between them is minuscule compared to the difference between professional players and an average person.

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