Human Hands vs. Water

Have you ever wondered why our fingers, palms, and toes get so pruny when they get wet? It's not simply that our glabrous skin swells up as water passes into its outer layer - the skin of people with nerve damage in their fingers does not get wrinkly. This occurrence is caused by blood vessels constricting below the skin.

Whether it is an adaptation or not is still debatable, but Mark Changizi and his colleagues at the 2AI Labs (followed by a group of British neuroscientists in 2013) found something interesting - we're better at handling wet objects when our fingers get pruny! In their study, conducted six years ago and published in Biology Letters, participants picked wet and dry objects with dry and with wet hands. Participants with wrinkly fingers were faster at picking up wet objects, while they were equally good at picking up dry objects as participants with dry hands. The researchers compare the effect of the wrinkles to rain treads in car tires.

Other studies on the subject were not as successful in confirming this, namely Haseleu et al. 2014 found no difference between the performances of participants with wrinkly or smooth fingers, and Taiwanese scientists in 2015 concluded that wet-wrinkly fingers decreased the performances in their tests.

What does Changizi say about this? According to the BBC, he wants to conduct a "safe" study where parkour pros will do their stunts with wrinkled or non-wrinkled skin, and then compare their performances. So let's see if it'll happen.

Our skin needs at least five minutes of exposure to water in order to get wrinkly, and this takes a longer time when we soak our hands in seawater than in freshwater. What could this mean? Wrinkly fingers could have allowed our ancestors to pick food from streams or wet vegetation with ease, and wrinkly toes then helped them to get a better footing when it rained. Apart from humans, only macaques are known to have pruny skin after soaking in water.

Common name:	Human
Scientific name:	Homo sapiens sapiens
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Family:	Hominidae