Those Wet, Grasping Fingers

Posted on January 9, 2013 by


This morning a colleague sent to the department, with a snide comment, an article that just came out in Biology Letters, Wet-induced finger wrinkles improve handling of wet objects. At first glance it looked like a joke or a hoax, but I opened the text anyway. On the second glance, after reading the first paragraph of the paper, I learned a new fact. It turns out that wet wrinkles are not simply a mechanical result of skin staying wet for too long. It’s actually an active response of the body mediated by autonomic nervous system. In other words, it looks like an adaptation designed by evolution for a specific purpose.

WetWrinkles

On the third glance, I noted that the second author of this paper is actually someone I know, and a respected member of the scientific community. In fact, he is a colleague at the Evolution Institute, the parent organization for this Forum.

On the fourth glance I read the complete paper. Fortunately, it is short and quite well written (in scientific writing the two properties are closely related).

However, as I earn much of my salary teaching undergrads scientific writing, I cannot resist doling out some advice to the authors of the article. You guys have gone too far in trying to appear scientific and overloaded the paper with ‘scientese.’ The first author is probably a graduate student, as they are particularly prone to this error.

Just consider the first paragraph:

The glabrous skin on human fingers and toes forms wrinkles in response to immersion in water. This wrinkling was previously thought to be the result of osmotic swelling of the stratum corneum, the outermost layer of skin [1]. However, more recent evidence has shown that it is in fact due to a reduction in the volume of the fingertip pulp, caused by vasoconstriction, which in turn is controlled by the autonomic nervous system [2–5]. In combination with the mechanical properties of the glabrous finger skin, this reduction in pulp volume results in the typical pattern of ridges and valleys on the tips of fingers and toes [1]. The dependence of finger wrinkling on the autonomic nervous system has led to the use of finger wrinkles as a clinical indicator of autonomic function [2,6–9].

What the hell is ‘glabrous’? Are my fingers ‘glabrous’? It turns out they are, and it is not some kind of a horrible skin disease. It simply means (according to Merriam-Webster dictionary) “smooth; especially: having a surface without hairs or projections.” The origin is Latin glaber, meaning ‘bald.’

I won’t comment on the rest of it. However, it worked its magic on me (well, I have to read and grade much, much worse…). It got the main idea across, which is that it is likely to be an evolved adaptation, which suddenly makes it interesting. And I don’t want to beat too much on the authors, as the rest of the paper is better. And as I said, it is admirably short (just three pages).

Actually, on the fifth glance, it was the second sentence in the abstract that did the trick: “The formation of these wrinkles is known to be an active process, controlled by the autonomic nervous system” (sorry about spending so much on the writing aspect, I sometimes obsess on these issues).

Also, as I learned on subsequent research (but could have realized simply by thinking about it) only the skin of fingers and toes wrinkles up after prolonged immersion in water.

The authors did a very simple experiment: soaking their subject’s fingers in water to get them wrinkled up, or not. Then the experimental subjects had to grab a bunch of glass marbles with their right hand, pass it through a hole to the left hand and place them in a different container. It turns out that wrinkled fingers made the job of handling wet marbles much easier. So there you have it. It is indeed an adaptation.

So the first glance was wrong. In fact, I’d like to nominate this paper for the ‘Anti-Golden Fleece’ award.

Golden Fleece

For those of you too young (or too old…) to remember, the Golden Fleece award was handed out by the late (and unlamented) senator William Proxmire. He particularly liked to give it to various scientific projects funded by the NSF. As blogger Orac wrote,

What they [Golden Fleece Awards] did, more than anything else, was to take cheap shots at worthy scientific projects that could easily be made to sound ridiculous to the scientifically ignorant. In other words, when it came to science the Golden Fleece Awards were anti-intellectual and anti-science to the core, more akin to demagoguery than anything else.

So, in my opinion, the paper on wet wrinkles deserves the Anti-Golden Fleece award. First, it apparently was very cheap to produce. I would be surprised if the authors spent on this research much more than £200, if that. Second, and even more importantly, it has a number of very interesting implications.

One of these implications that immediately struck me was the connection to Omega-3 oils. The article doesn’t make this connection, but to me it was obvious, probably because the diet of early humans has been much on my mind lately (take a look here and here).

omega-3-fish-oil

It has become increasingly clear that Omega-3 fatty acids are absolutely essential for normal development and functioning of Homo sapiens. Recent research in British juvenile prisons showed that giving inmates Omega-3 oil supplements dramatically reduced their anti-social behaviors. Evidence accumulates that getting enough Omega-3 oils is critical for normal development of children. My parents made me drink horribly tasting fish oil, which I hated them for, but now I am grateful.

What does this have to do with wet wrinkles? Well, it turns out that the main sources of Omega-3 oils are various kinds of seafood. But how did our species become dependent on this critical source of nutrients, which we cannot synthesize and must get from food? Various people proposed that early modern humans must have evolved in, or near an aquatic environment. One line of evidence for it is that we have naked skin. This is a typical evolutionary development in aquatic mammals (think dolphins or seals).

Human_and_dolphin

Another one is our heavy dependence on Omega-3 oils that are most easily obtained from aquatic food sources. This means that early humans must have spent a lot of time in water, and ability to handle wet, submerged objects dexterously was highly evolutionary advantageous. If this is right, wet wrinkles evolved as a way for us to efficiently harvest mussels and other shellfish, or perhaps grab those fish full of yummy and healthful Omega-3 acids!

mussels

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