Sumo wrestlers: they're huge. The huger the better. End of story, right?
Of course not — sumo wrestlers practice strict training including a special diet and they even live in sumo communes called 'heya'. But one thing that science has found to make a good sumo, and something the athletes unfortunately don't have control over, is the length of their fingers. Specifically, the ratio of the lengths of their ring to index fingers.
You've all heard about the digit ratio thing right? It seems to come up in bars as a flirting mechanism, but drunken flirters tend to use the wrong fingers or the wrong ratio. Here's a simplified explanation: if your ring finger is longer than your index finger, you were exposed to more testosterone in the womb than if your index finger is longer, in which case you were probably exposed to more estrogen. Women tend to fall into the latter category, men the former, although ratios vary widely. Mine appear to be almost the same. In the picture below, the ring finger is longer, so the ratio is low, which indicates higher testosterone exposure in the womb.
Scientists have studied the so-called 2D:4D (d is for digit) ratio as it relates to sperm count, penis size ("under anaesthesia, flaccid and stretched penile lengths were measured," not kidding), eating disorders, handwriting, financial trading, musical ability, just to name a few. The list is long. Maybe sumo wrestling was the only thing left?
Handily, the sumo museum in Japan collects wrestlers' handprints. So Tamiya et al, who published their work in the October 10 issue of Evolution and Human Behavior, examined some of those handprints and found that a lower 2D:4D ratio in sumo wrestlers was associated with "higher sumo ranks and better winning records." But the association was not as strong as with other sports like soccer and skiing, so the authors theorise that testosterone exposure in the womb is more important for athletes that require endurance rather than those who like sumos require explosive power.
The experts say that the hormonal influence on finger length happens in utero. But the study made me wonder if sumo wrestlers' large amounts of fat, which are associated with higher levels of estrogen, might have some influence in finger length over time? Just a thought from me, a curious non-scientist. Scientists, please educate me (nicely) in the comments! [Evolution and Human Behavior via Scientopia]