We have useless things in our bodies that are remanents from our early ancestors.
See especially this excellent description of eight vestigial items in our bodies.
See also this http://en.wikipedia.org/wiki/Human_vestigial Human Vestigiality article for evidence for vestigial features of ...
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The <hl>erector pili</hl> are smooth muscle fibers that give humans "goose bumps".
If the erector pili are activated, the hairs that come out of the nearby follicles stand up and give an animal a larger appearance that might scare off potential enemies and a coat that is thicker and warmer.
Humans, though, don't have thick furs like their ancestors did so we get goose bumps in situations that cause animals' hair to stand on end.
Here's an elaboration on our vestigal tail:
Humans have a tail bone (the coccyx) attached to the pelvis, in the same place which other mammals have tails. The tail bone is formed of fused vertebrae, usually four, at the bottom of the vertebral column. It doesn't protrude externally, but retains an anatomical purpose: providing an attachment for muscles like the gluteus maximus.
Human embryos have a tail that measures about one-sixth of the size of the embryo itself. As the embryo develops into a fetus, the tail is absorbed by the growing body. The developmental tail is thus a human vestigial structure. Infrequently, a child is born with a "soft tail", which contains no vertebrae, but only blood vessels, muscles, and nerves, although there have been a very few documented cases of tails containing cartilage or up to five vertebrae. Modern procedures allow doctors to eliminate the tail at delivery.
Design One: The Pharynx
The human pharynx is the part of the throat that begins behind the nose and leads down to the voice box. It does double duty as a tube for breathing and for swallowing. But when you're swallowing you can't breathe, and when you're breathing you can't swallow. That's why humans run a serious risk of choking if the pharynx doesn't close at the right time when eating.
Curiously, human infants under six months and chimpanzees don't have this problem. But infants and chimps can't talk, and without our uniquely situated pharynx we wouldn't be able to talk either.
Design Two: The Birth Canal
The Bible says that God punished Eve and her female descendants with painful childbirth because she partook of the forbidden fruit. Presumably, childbirth would be a snap if not for that damned curse. And not only has pain long accompanied childbirth, but so has death. The rate of mothers dying during childbirth in the United States in 1900 was about 65% higher than it is today.
You could blame God, or Eve, or the serpent. Or you could point the finger at bipedalism--walking upright on two legs. This evolutionary innovation forced a smaller pelvis on us. But bipedalism isn't the whole story. Humans have evolved big brains, and we needed a big container to hold those brains. This is why human infants are born more premature and helpless than other mammals. Babies need to get through the birth canal before their heads get too big.
Design Three: The Jaw
The human jaw has too many teeth for its size. Many people have no room for wisdom teeth (third molars) if they get them, and a lot of people's teeth have to fight one another for limited territory, leading to crooked teeth and orthodontists. Impacted wisdom teeth can result in serious infections, and before modern dentistry these late eruptors could be deadly. If you couldn't eat, you died.
Design Four: The Appendix
This is a case of a vestigial organ if ever there was one. The human appendix has no known function, except perhaps to put money in surgeons' pockets. About the size of a finger, this organ is located at the beginning of the large intestine. Undigestible food that enters the appendix is normally forced out by muscular contractions. But when it isn't, the result is a potentially deadly infection.
The appendix is related to a digestive organ found in many other vertebrates. This is the cecum (pronounced SEE-cum), and it's largest in herbivores, where it helps to digest plant matter. Since evolution isn't keen on cleaning up after itself, we're left with a useless and potentially life-threatening organ. In fact, NASA is so concerned about appendixes bursting in outer space that it's considering requiring appendectomies prior to future long-term missions.
Design Five: The Spine
The spines of four-legged mammals work well horizontally. But when the spine stands up vertically, as in humans, it creates a lot of pressure on the vertebral discs. These discs can become compressed and slip, causing herniated discs and all manner of back pain and expensive therapy.
E.g. Leg and pelvic bones in whales, dolphins, and some snakes; unused eyes in blind cave fish, unused wings in flightless birds and insects; flowers in non-fertilizing plants (like dandelions); in humans, wisdom teeth, tailbones, appendix, the plantaris muscle in the calf (useless in humans, used for grasping with the feet in primates).