It seems nuts, but the relative lengths of ring and index fingers in humans have been linked to exposure to pre-natal sex hormones. Pretty abstract, right? But here's a new, concrete result: those relative lengths are very strongly associated with different degrees of prostate cancer risk.
A study led by the University of Warwick and the Institute of Cancer Research talked to over 1500 prostate cancer patients (and twice as many control subjects) from 1994 to 2009 about the length of their fingers. The men compared their own hands to pictures of variously proportioned finger-lengths, and picked the one that best matched their own (right) hand. Most of the men had index fingers shorter than their ring fingers, or of even lengths. And their prostate cancer risks were normal. But some men had index fingers longer than their ring fingers—and those guys had a 33% reduced risk of prostate cancer. And, this was even more true in men under age 60, whose unusual finger-lengths were associated with an 87% reduction in prostate cancer risk.
What is up with this? Well, the relative lengths of ring and index finger may be related to pre-natal exposure to sex hormones: specifically, less testosterone in the womb seems to lead to a longer index finger—and reduced prostate cancer later. The reason to be excited about this finding is that, increasingly, medical protocols suggest that testing younger men for prostate cancer is futile, or even detrimental. But men who get prostate cancer younger are likely to have a more aggressive form of the disease. So how to figure out who to test?
"Our results show that relative finger length could be used as a simple test for prostate cancer risk, particularly in men aged under 60," says joint senior study author Prof. Ros Eeles. "This exciting finding means that finger pattern could potentially be used to select at-risk men for ongoing screening, perhaps in combination with other factors such as family history or genetic testing." In other words, this finding could point to more efficient testing. But more likely, it will lead to yet more research before any concrete guidelines are offered. "Our study indicates it is the hormone levels that babies are exposed to in the womb which can have an effect decades later," said co-joint author Prof. Ken Muir. "As our research continues, we will be able to look at a further range of factors that may be involved in the make-up of the disease."