Wings on a flightless bird, eyes on a blind fish, and sexual organs on a flower that reproduces asexuallyâ€”the casual observer might ask, whatâ€™s the point? But these vestigial organs and structures, once useful in an ancestor and now diminished in size, complexity, and/or utility, carry important information and give us clues to our evolutionary past.
Though humans often think of vestigial organs as useless little fixtures that sometimes, as in the case of the appendix, cause us extreme anguish, we wouldnâ€™t know nearly as much about macroevolution as we do now without their presence. In On the Origin of Species, Charles Darwin used vestigial organs as evidence for evolution, and their presence has helped define and shape our phylogenetic trees.
Why the Leftovers?
Contrary to what most think, vestigial doesnâ€™t necessarily mean useless; in some cases, we may just not yet know exactly how the organ is used in its current incarnation. (The human thymus was once thought to be vestigial). Because these structures can be traced back through the ancestors, they essentially serve as a marker of evolution; no organism can have a vestigial organ that hasnâ€™t been found in its forefathers. For this reason, you wonâ€™t ever find feathers on a mammal or gills on a primate.
One striking example of an atavism is the human coccyx, or tailbone, which is a relic of the mammalian tail. Useful for mammals that use tails for balance, species-to-species signaling, and support, the tail is missing in apes and in humans. However, all human embryos initially have a tail. Normally, they regress into four to five fused vertebrae (the coccyx). However, there have been numerous case studies of human children being born with an extended coccyxâ€”a tailâ€”that was removed without incident. Ranging from one inch to five, the gene that normally stops vertebrae elongation is decreased and the human tail remains at birth.
When we get goose bumps, itâ€™s the action of muscle fibers called erector pili, which cause the hairs in follicles to stand to attention. In animals, such as a cat, this causes a larger appearance and can be used to thwart an attacker, as well as trap air between feathers and fur for insulation. However, humans, with our minimal coating of fur, donâ€™t really need the raised hair; we use jackets instead. It is therefore thought that goose bumps donâ€™t really serve much of a purpose. However, the small expenditure of energy used to contract the muscles could, perhaps, cause a tiny release of heat. Or, because goose bumps are associated not only with cold, but emotional responses as well (listening to a good song, seeing a scary movie) they could now serve as a form of communication with others.
More at Divine Caroline
Ah, the tailbone. What a pain in the ass…literally. I fell down my cellar stairs a couple of years ago and fractured my coccyx. It still hurts if I sit wrong. Forget hard benches.
7 thoughts on “Seven Evolutionary Leftovers in the Human Body”
I too have injured mine tail bone. Thank god for pain killers.
@tiki god: Yep Yep
Percoset 10/325, Fentanyl 50mcg/h, mobic 7.5mg, flexiril 10mg, elavil 75mg
It’s insane, but w/out ’em, I’m practically in a wheelchair. At least I’m not using a cane anymore. One of the advantages of being a public school teacher is the ability to take large amounts of time off. I’m basically out for 18 months…paid. 🙂
Hooray for the third eyelid! I wish i could use mine, they seem useful.
@thelotuseater725: Certainly helped Spock out.
Nipples are like male plumage! Just not as nice as on the females!
And people complain that you need to be paid more (I’m kidding, of course).
@RSIxidor: I know. The teachers’ unions will be the death knell of competent teachers and our public education system. There are more than a few teachers I know that really need to go. Most teachers burn out w/in 5 years. Unfortunately too many keep teaching anyway. If you want to teach, you have to love it and keep learning yourself. I get a 1 year sabbatical every 5 years and it supposed to be used for making yourself a better, more competent teacher. Take more classes, research, anything really that gains you better and more detailed knowledge for whatever subject you teach. Needless to say that is almost never what we actually do. I’ve gone back to college to take courses that I’d hadn’t already taken (they’re always adding new and updated courses) or more education classes (which is good for me because I never took any prior to teaching).
I agree w/ you…sorta. 😉