Happy times, everyone! It’s Darwin Day – an international celebration of the birth of the world’s most famous and influential evolutionary biologist, who came into being on February 12, 1809.
The evidence for evolution through natural selection is as beautiful as it is utterly overwhelming. Every part of our own biological architectures – from walking upright to the way our eyes work – is a piece of evidence pointing toward Darwin's elegant theory. Rather conveniently, some of these you can physically see or experience with minimal effort, so let’s have the briefest of looks at our favorites.
1 – The Missing Muscle
If you place your forearm onto a desk with the palm of your hand facing upward, and you make your thumb and pinkie finger touch, one of two things should happen. Either a tendon in your forearm rises up or it doesn’t. If so, then congratulations, that tendon is connected to the palmaris longus, a muscle that’s designed to “help with wrist flexion” – essentially, the bending of your wrist.
Not everyone has this muscle; in fact, a small but significant proportion of the global population doesn’t have this muscle at all on one or both of their arms. Although you can find this in primates that often use their forelimbs to move around, it makes no effect in humans whether it’s there or not, which suggests that in humans, this muscle is vestigial – ancient and functionless.
It’s developed in lemurs and monkeys, but shorter in evolutionary cousins that do far less climbing around. A sublime example of evolution in action, per Vox.
2 – Chin Up
This may come as a complete surprise to you, but as noted by The Smithsonian, we’re the only hominids with (true) chins. Despite being closely related to bonobos, chimpanzees, and the like, we possess a bony lump at the end of our lower jaw, but why?
Various hypotheses abound. One study suggests it evolved in response to the way in which we speak; another indicates it helps support the jaw while we chew. One disagrees and instead concluded that it was sexually selected. Either way, we have chins, and our evolutionary cousins don’t, thanks to a quirk of evolution we’re yet to properly comprehend.