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A vestigial structure is a genetically determined attribute that, through the evolutionary process, has lost some or all of its original function. Perhaps the most famous example is the appendix, which in humans has lost most of its ancestral use.

Evolutionary anthropologist Dorsa Amir started a Twitter thread explaining the phenomena. Amir is a postdoctoral researcher with Boston College.

The Twitter thread begins with a basic explanation of the structures.

It seems she just wants to watch the world learn.



The reason we know the Palmaris longus was used for getting around trees is because we share a common ancestor with primates. For example, the orangutan still uses that muscle and it is well defined. While some of our closest relatives, such as the gorilla or chimpanzee, do not employ the muscle, it still shows up in similar rates as on us.



Darwin's Tubercle was originally named the Woolnerian Tip, named for Thomas Woolner who depicted it in one of his sculptures. While the tubercle is possibly a vestigial structure, it's also possibly formed by environmental factors.



The tailbone is also known as the coccyx, which is just fun to say. There are some who claim we still need the tailbone, evidenced by the various bits of musculature attached to it. However, most coccygectomy studies show it produces little to no disadvantages for someone without one.



In birds and lizards, this third eyelid covers the eye for protection. While it doesn't perform this function in humans, the plica semilunaris is not without use. During eye movement, it helps us maintain tear drainage.



You've likely also encountered goose bumps in connection with hearing a really good song. This is because music can react in the brain similar to tangible ingestions like food or even psychoactive drugs. The dopamine release changes your breathing, temperature and heart rate, activating the goose bump response.



The grasp reflex is very strong in infants. Imaging has actually shown they can perform the action in utero. Nowadays, the grip is still strong, but not reliable. They may let go without warning. (Please do not try and pick up your child this way.)



After the thread, Amir took questions from the class.





Amir is a researcher for Boston College, studying human behavior. She and other researchers recently published a paper about the impact of your childhood socioeconomic status on your adult preferences.

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