Sunday, April 12, 2020

Twitter Thread: The Human Body's Evolutionary Leftovers


Awesome, our bodies are like natural history museums. Apparently, we're brimming with evolutionary leftovers, and Dorsa Amir mapped out a way to play around with some of these in a fun Twitter thread. 

1.

Text - Dorsa Amir @DorsaAmir · 1d 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) O 512 2721K 48.8K

2.

Text - Dorsa Amir @DorsaAmir · 1d Replying to @DorsaAmir 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) present absent

3.

Wildlife - Dorsa Amir @DorsaAmir · 1d Replying to @DorsaAmir 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)

4.

Joint - Dorsa Amir @DorsaAmir · 1d Replying to @DorsaAmir 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)

5.

Eye - Dorsa Amir @DorsaAmir · 1d Replying to @DorsaAmir 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) plica semilunaris

6.

Text - Dorsa Amir @DorsaAmir · 1d Replying to @DorsaAmir 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)

7.

Text - Dorsa Amir @DorsaAmir · 1d Replying to @DorsaAmir 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)

8.

Text - Dorsa Amir @DorsaAmir · 1d Replying to @DorsaAmir 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)

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