HUMAN VESTIGIALITY

Published March 14, 2013 by Tony

HUMAN BODY EVOLUTION
11 USELESS ORGANS

From the time of prehistoric man on, the human body has evolved continuously and adapted significantly, and today only a few biological traces of our prehistoric ancestors remains in us which, despite almost without any use, are still part of our body. In the context of human evolution, human vestigiality involves characters, such as organs or behaviors, occurring in the human species that are considered vestigial, in other words having lost all or most of their original function through evolution.
Here’s the main ones.

plica semilunaris11. Plica semilunaris
In the inner part of the eye, the two eyelids form a small indentation called “inner canthus”, occupied by a small red protuberance, the “caruncula lachrymalis”, just external to the small and vertical fold of conjunctiva (that we can see), called “plica semilunaris.” This small fold of tissue near the tear duct, is a vestigial remnant of the nictitating membrane (persisting through evolution) which is drawn across the eye for protection, but performing no function in man. Despite reduced in humans, it represents a third eyelid present and fully functional in many  animals such as birds, reptiles, and fish.

prehistoric man10. Body Hair
Without a doubt, once human being was much more hairy. Up to about 3 million years ago, our body was almost completely covered by hair. Since “Homo erectus” onwards, the different capacity of perspiration (through a better body thermo- regulation) slowly led body to lose hair, now useless.

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paranasal_sinuses09. Paranasal sinuses
These are a group of four paired air-filled spaces that surround the nasal cavity above the eyes and present in a variety of animals. The human biological role of the sinuses is debated, but a number of possible functions have been proposed among which increasing resonance of the voice or providing a buffer against blows to the face.

Adenoids08. Adenoids
They are a mass of lymphatic tissue situated posterior to the nasal cavity whose function is to be a trap for bacteria, and for this prone to hypertrophy and infection. Normally, in children the adenoids are bigger, often removed to avoid constant infections and  lack of airflow, though their size reduce with age. Useful to protect prehistoric man, over time this gland has lost importance for the improved hygienic conditions of life.

tonsil07. Tonsils
The term most commonly refers specifically to the mass of lymphatic material situated at either side at the back of the human throat. They represents the immune system’s first line of defense against ingested or inhaled foreign pathogens, and because of this tonsillitis are very frequent during youth, obliging their surgical removal. However, the fundamental immunological roles of tonsils have yet to be understood. Tonsils tend to reach their largest size near puberty, and they gradually undergo atrophy thereafter. As for the adenoid, their presence is not indispensable.

coccyx06. Coccyx
The tailbone or coccyx is the remnant of a lost tail. All mammals have a tail at one point in their development; in humans it only is present for a period of 4 weeks, during embryogenesis. The coccyx, located at the end of the spine, has lost its original function in assisting balance and mobility when it was a real tail.

muscles of the auricula05. Erector muscle of hairs / muscles of the auricula.
Diverse muscles in the human body are thought to be vestigial, either by virtue of being greatly reduced in size compared to homologous muscles in other species, by having become principally tendonous, or by being highly variable in their frequency within or between populations. Humans and other primates however have ear muscles that are minimally developed and non-functional, yet still large enough to be identifiable. Among them the arrectores pilorum, and the muscles of the auricula. The Erector muscle of hairs are small muscles attached to hair follicles in mammals whose contraction causes the hairs to stand on end – known colloquially as goose bumps. Useful in many animals, they have lost their utility for humans. Humans and other primates have ear muscles that are minimally developed and non-functional which in other animals give, for instance, the chance to move the ears in various directions.

wisdom Teeth04. Wisdom teeth
These teeth are vestigial (third) molars that human ancestors used to help in grinding down plant tissue. The skulls of human ancestors had larger jaws with more teeth, used to help chew down foliage and compensate the lack of ability to digest the cellulose. As human diets changed, smaller jaws were naturally selected, but the third molars, or “wisdom teeth,” still commonly develop in our mouths. Currently, wisdom teeth have become useless and even harmful to the extent where surgical procedures are often done to remove them.

appendix03. Appendix
The vermiform appendix is a vestige of a small organ that in ancestral species had digestive functions. Darwin argued that it was helpful to digestion during the years in which primitive man ate more plants and vegetables, rich in starch. Therefore, its usefulness is diminished with the evolution, when we started eating more digestible foods.

hymen02. Hymen
It is to say the membrane that surrounds or partially covers the external vaginal opening. Some scientists view the function of hymen in young girls as a protective membrane that protects the reproductive system from infection in the embryonic period and protect the fertility of young girls before mating. Anyhow, this is another organ of which human being wouldn’t feel the lack.

nipples01. Male Nipples
In the anatomy of mammals, a nipple, is a mammary papilla whose physiological purpose is to deliver milk to the infant, produced in the female mammary glands during lactation. The presence of nipples in male mammals is a genetic architectural by-product of nipples in females, best explained as a genetic correlation that over time persists through lack of a better or different evolution of the male.

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