Thursday, April 9, 2015

Finger Envy

A fun tidbit has emerged from the news today (thanks to Dr. Steve King for this one): Researchers in England measured the pointer-to-ring-finger ratio of hundreds of runners at a road race and found that men with longer ring fingers were faster. So how to interpret this?

A low finger ratio (longer ring fingers) has been found to be strongly influenced by fetal exposure to high levels of testosterone. So, faster runners are more likely to have experienced high fetal testosterone, which is interesting because this exposure is associated with all kinds of things that enhance male reproductive fitness-- sperm count, sex drive, spatial awareness (!), etc. Finger ratio is sexually dimorphic: that is, males have lower ratios, on average, than females. Sexual dimorphism suggests that males and females were subject to different evolutionary pressures at some point.*

Putting this together, the researchers suggest that male endurance running ability was preferred by our female ancestors, perhaps because it was a signal of physical fitness and other positive attributes, in the same way that peahens select peacocks with the best trane of feathers. This makes sense, they say, if we accept that males were persistence hunting.  So not only would persistence hunting have had a direct selective advantage (ability to acquire food translates directly to increased ability to survive and reproduce) but it may have been propelled into anatomical adaptation by sexual selection, driven by female choice. A very cool idea, but the implicit assumption here is that Homo was a persistence hunter.  And we just don't know that.

Aside: I had floated the idea of human running as an example of costly signalling-- risky behavior rewarded more through increased reproduction than through a direct benefit such as increased food acquisition,etc- early on in my planning phase of my first research project. But I couldn't think of any way to test this so I abandoned it. I guess what makes a good scientist is the ability to come up with a way to test hypotheses rather than sitting around chewing cud!

The primary research article

Secondary source

Update: my finger ratio is .92, nice and low. So I've got that going for me. Funny though, I don't feel super manly.
*Edit: sexual dimorphism in finger ratio is, obviously, just due to higher fetal testosterone in males, not different selective pressures. Brainfart.

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