Let's start our Top2Toe series not with the top, but with the toe!
It's a well-known fact that our fingers and toes wrinkle when exposed for a moderate amount of time in water. There have been myths about why this is the case, one of which being that they absorb water. While the cause has not been empirically proven, the best theory put forward in my opinion is that of Mark Changizi of 2Al labs.
He thinks that the ridges formed by wrinkling prevent slipping on surfaces by increasing friction between fingers and toes, and what they lie on. This idea makes sense because, if we think about a long-gone scenario, back when our ancestors used four limbs to commute, the hands and feet were all on the ground. The bottom of a rock pool is very slippery when you get in, but does that mean that after a while in it, you become less likely to slip? Is that due to getting used to it, or due to wrinkling of toes and (if you use them) fingers?
Speculation about this somewhat trivial topic abounds, but what about the shape of our big toe compared to other primates? Read the next post on the evolution of our feet, and how past environments have shaped them.