Thread by @DorsaAmir

Did you know the human body is full of evolutionary leftovers that no longer serve a purpose? These are called vestigial structures and they’re fascinating. (1/8)

Put your hand flat on a surface and touch your pinky to your thumb. Do you see a raised band in your wrist? That there’s a vestigial muscle called the palmaris longus. It used to help you move around the trees. About 14% of us don't even have this muscle anymore. (2/8)

Check out your ear. Do you see this little bump? That’s called Darwin’s tubercle. It used to help you move your ears around. Now that we have super-flexible necks, we don’t need these anymore. (3/8)

Here’s a more obvious one: the tailbone. This is the ghostly remainder of our lost tails, which were useful for balance & movement in trees. We still grow tails as embryos, but then attack and destroy them in the following weeks. Not the most efficient system. (4/8)

Ever wonder what this little pink thing in your eye is? This is the plica semilunaris. It used to be a third eyelid that would blink horizontally. You can see this in action in the eyes of many other animals. (5/8)

Oh, and you know how you sometimes get goosebumps when you’re cold or scared? That’s a vestigial reflex that used to raise body hair to make you appear bigger or trap an extra layer of heat for warmth. Some people can actually do this on purpose. (6/8)

Another cool reflex is the palmar grasp reflex. If you place your finger on an infant’s palm (or feet!), they will try to grasp it. Ancestral primate babies would have used this to grasp on to their parents for transport. (7/8)

These are just a few pieces of evolutionary baggage handed down to you from your primate ancestors, among others. Your body is basically a natural history museum! (8/8)

A few addendums:

Wisdom teeth — yes, though still ~functional for original purpose.

Appendix — potentially yes, though it still seems to do stuff (may have been repurposed).

Male nipples — though technically non-functional, not quite vestigial. Due to embryonic development.

Additional footnote:

I think the diagram I randomly pulled off Google Images yesterday isn't as precise as it should be. *This* is the plica semilunaris.