Vestigial structures: evolutionary remnants in the human body

Zoology

Relics of Human Evolution

Vemeonasal organ. The vemeonasal organ is a little pit on each side of the septum that is lined with nonfunctioning chemoreceptors. It may have been used for pheromone-detecting ability.

Extrinsic ear muscles. These three muscles most likely made it possible for prehominids to move their ears independently, in the manner of many mammals, such as rabbits and dogs. Many people can learn to wiggle their ears because of these muscles.

Wisdom teeth. Early humans had to chew a lot of plants to get enough calories to survive, so another row of molars helpful. Today, only about five percent of the population has a functioning set of these third molars, which are often removed to avoid problems when they don't fully emerge or emerge sideways.

Neck rib. A set of cervical ribs appear in less than one percent of the population. They often contribute to nerve and artery problems, and these leftover ribs don't seem to be of much help with regard to movement and flexibility.

Third eyelid. Some common ancestor of birds and mammals may have had a membrane for protecting the eye and that could also have functioned to help sweep out debris. It is believed that humans retain only a tiny portion of this membrane in the inner corner of the eye.

Subclavius muscle. This small muscle stretching from under the shoulder from the first rib to the collarbone has no purpose since humans don't walk on all fours. Some people have one, some have none, and a few have two.

Palmaris muscle. This long, narrow muscle runs from the elbow to the wrist. Only about 11% of modern humans have this muscle. It may once have been important for hanging and climbing. Surgeons harvest it for reconstructive surgery.

Male nipples. This lactiferous ducts form well before testosterone causes sex differentiation in a fetus, causing some scientists to believe that the female version of the body is the basic template. In fact, men have mammary tissue that can be stimulated to produce milk.

Erector pili. The are the bundles of smooth muscle fibers that enable animals to puff up their fur for insulation or to raise their hackles to intimidate others. Humans have retained this ability except that we refer to them as goose bumps and the amount of hair that is impacted has been substantially reduced.

Appendix. This narrow, muscular tube is attached to the large intestine and is believed to have served as a special area to digest cellulose when the human diet consisted primarily of plant matter. The structure also produces some white blood cells and quite often becomes infected.

Body hair. Brows help keep sweat and dirt from the eyes and make facial expressions more salient. Armpit and torso hair redirects sweat from the body core so that it may help with cooling. Male facial hair may play a role in sexual selection. Apparently most of the hair left on the human body serves very little function, other than to help detect bugs that might jump onto limbs and can pose a danger if they are poisonous.

Plantaris muscle. This small muscle was useful to other primates for grasping with their feet, but only nine percent of the population has this muscle today.

Fifth toe. Lesser apes use all their toes for grasping or clinging to branches. But the big toe in humans can only really be used for balance while walking upright or standing.

Coccyx. These fused vertebrae are all that is left of the tail that most mammals still use for balance and communication. Tails are not needed in humans because they walk upright and spend less time in trees than their primates.

Paranasal sinuses. These nasal sinuses may help to capture bacteria and viruses as they are lined with mucus. The also make the head lighter and to warm and moisten the air we breathe. The sinuses of our early ancestors may have helped with survival if they were lined with odor receptors that gave a heightened sense of smell.

Extinct Animals

Steller's sea cow. The Steller's sea cow or Hydrodamalis gigas was a large herbivorous marine animal of the order Sirenia. Its closest living relatives are the manatees and the dugong. The sea cow was abundant throughout the North Pacific, but because it was such a slow-moving animal, it was hunted to extinction within 27 years. It was first described by Georg Wilhelm Steller, an expedition naturalist, in 1741. An average weight was about 8 to 10 tons. It looked much like a large seal but had two forelimbs, a whale-like fluke, no actual teeth (just flat wide bony plates top and bottom), thick and black skin, with a head small in proportion to its body. The Stellar sea cow did not come to shore, but remained in the sea though it could not submerge. The aboriginal hunting of sea otters may have increased sea urchins, which would have reduced the amount of kelp available to the Stellar's sea cow -- kelp was its primary food source.

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