I did a blog ages ago about vestigial (or left-over) traits in humans but I was doing some reading and found some more info and thought I’d post a list (some are pretty weird).
In no particular order:
In humans it’s more or less useless (though some have suggested it may house useful bacteria to prevent them from being wiped out by certain immune responses, but many vestigial organs are modified to new tasks). In other mammals, specifically herbivores, it is used to digest cellulose from plants. In other words it’s a stomach for digesting… well, paper essentially. But not in us. At least not any more : )
The tail bone.
This is in humans all that remains of the tail we all lose in the womb. Sometimes people are born with tails, but I’ll spare you the photos. Instead here’s a picture of a human fetus with a clearly visible tail:
We are also covered with a thin coat of fur all over our bodies in the womb which we usually shed before birth called lanugo:
All humans literally have fur and tails at one point of development… hmmm…
Extra teeth for chewing plants, now too many for most mouths to hold. In some populations (including some aboriginals) these teeth are virtually univeral, and in others (like the indigenous peoples’ of mexico) they are virtually non-existent (at least according to wikipedia).
The ability to wiggle your ears.
This is found in some humans (not all), and is a greatly diminished version of a trait common in many primates. Primates however often anatomically can’t move their heads left or right very far. Humans can move their heads a great deal and it’s extremely common to see someone turn their head to try to hear something in the distance or pinpoint where a sound is coming from. But our ancestors apparently couldn’t do this and had to turn their ears instead. Even people who can’t move their ears often have the muscles to do so, they just don’t work.
This is probably the weirdest. Ever notice that little triangular thing in the inside corner of your eye?
Or maybe you’ve seen it in your cat’s eye?
It’s actually a non-functional transparent third eyelid (seems to close a bit more in cats though). In some birds, mammals, reptiles and fish it still works like so:
It allows them to blink while still being able to see. But not you : P
Only one primate species has a third eyelid that still functions, and it’s this dude:
Men and women are somewhat commonly born with extra nipples (and even extra breasts) and these usually follow the vertical line pattern of other mammals with multiple nipples, like dogs and cats. Funny coinkidink idn’t it? I will again spare you the photographic evidence.
The cling-to-your-momma reflex.
This one was new to me but apparently the automatic reflex if you put something in the palm of an infant is to cling to it, and hard. Tiny infants can hold their own body weight, you can even dangle them they can grasp so strongly. This mirrors what is found in other primates and apparently exists because the mother needs her arms free to climb into a tree to flee a predator, which is for many primates the only line of defense. So she scoops up the baby and it clings on to her hair instinctively (and effectively). But since humans a) don’t have natural predators, b) don’t live in trees and c) don’t have enough hair to cling to, this is considered a vestigial or left-over trait. Still pretty interesting though.
No, not the dime-a-dozen “scary” kid’s books that were popular when I was in gradeschool. The bumps you get on your skin when you’re scared or cold. Isn’t it kind of weird to get bumpy skin when you’re cold or frightened. Why cold or frightened? I’ll tell you why. Because once upon a time our ancestors had long hair all over their bodies and they didn’t just get bumps, their hair stood on end. This, in the animal kingdom, has two advantages – it makes many animals appear larger which helps them scare off or intimidate predators, rivals etc. And two, when the hair stands on end it creates pockets of air in between the individual hairs which traps warm air leaving the body, helping to insulate them against the cold the same way a wind breaker does. But again, we don’t have hair any more so we just get weird little bumps where hair used to be in our distant past.
Scurvy is an illness we get when we don’t have vitamin C for a long time. We’re basically the only mammals that get it. Why? Because the gene that is responsible for making vitamin C functions in all but a few mammal species, and one of them is us. We have the gene, but it’s broken.
Anyway, that’s my updated list of weird left-over traits in human evolution. There are lots more but these are the interesting ones. Hope you enjoyed.