Useless body parts

Most people know the appendix is a vestigial organ, a body part that no longer serves any function.

But it’s hardly the only one. Our bodies are littered with bits and pieces that serve no apparent function. Some are leftovers from ancient ancestors, others leftovers of prenatal development, just hanging around the body because they’re not bothering anybody and so there’s no reason for them to leave.

In the June issue of Discover Magazine, Jocelyn Selim has compiled a useful list of these useless organs. Some may surprise you.

Consider the paranasal sinuses. Mine are quite thoroughly stuffed up at the moment. What good are these mucus-lined cavities?

For humans, very little. They do make our heads lighter and they help warm and moisten the air we breathe (a benefit in cold, dry Saskatchewan winters), but that’s it. In animals with an acute sense of smell, however, the sinuses are lined with olfactory tissues. Our ancestors probably had a far more acute sense of smell (our DNA contains broken genes for additional odor receptors) but for some reason we lost that ability; all we’re left with are sometimes troublesome holes in our heads

Speaking of troublesome, wisdom teeth are also on the list of useless body parts. Sprouting in late adolescence, these molars seldom develop normally; I’ve had two pulled myself. Only five percent of the human population has a healthy set.

Why, then, do we have them? Because early humans had to chew a lot of plants to get enough calories to survive, and chewing plants is tough on teeth. The wisdom teeth were intended to replace other teeth lost to wear. With the rest of the teeth staying healthy, there’s no room for them.

The appendix, a narrow, muscular tube attached to the large intestine, was also of use in our plant-chewing days; it was a special area for digesting cellulose. With our modern diet, we no longer need it, and, again, we’re mostly only aware of it when it becomes inflamed and has to come out.

The tailbone, or coccyx, a set of fused vertebrae at the bottom of the spinal column, is another useless vestige of our ancestral past: it’s all that’s left of our tails, which disappeared from hominids before they began walking upright.

Even our toes are largely vestigial. The lesser apes use their toes for grasping branches, but the only toe we really use is the big toe, which helps provide balance for walking upright.

And then there’s body hair. Animals, of course, can puff up their fur for added insulation or to scare off attackers. We retain the muscle fibers for this, called erector pili, but with so little hair on our bodies, all we can manage are goosebumps, which neither warm us nor make us look intimidating (unless you find plucked waterfowl intimidating).

We have other useless muscles. The extrinsic ear muscles allow many animals to move their ears independently of their heads–all we can manage is a slight wiggle. The subclavius muscle, stretching under the shoulder from the first rib to the collarbone, would be useful if we walked on all fours but is so useless now that some people don’t even have it.

Eleven percent of us also lack the palmaris muscle, a long, narrow muscle that runs from the elbow to the wrist that may have been important when we were tree climbers, and nine percent of us have lost the plantaris muscle, useful for gripping things with your feet. And more than 20 percent of us are missing the pyramidalis muscle, a tiny, triangular pouchlike muscle attached to the pubic bone that may be a relic from the days of our pouched marsupial ancestors.

Other useless body parts include the vomeronasal organ, a tiny pit in the nose lined with nonfunctioning chemoreceptors that may once have been used to sense pheromones; the third eyelid, retained as only a tiny fold in the inner corner of the eye, that may once have been a proper eyelid for protecting the eye and sweeping out debris; male nipples (present because milk-producing ducts form in an embryo before sex differentiation); the male uterus (a remnant of an undeveloped uterus that hangs off the male prostate gland); and the female vas deferens, or epoophoron, a cluster of useless dead-end tubules near the ovaries.

In a way, our bodies are zoos for endangered body parts. As Joceyln Selim’s Discover article points out, in a few more millennia some of these may vanish entirely.

Appreciate them now before they’re gone!

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