Friday, June 22, 2007

Useless organs?

According to Brandon Miller of, Charles Darwin mentioned in his On the Origin of Species (1859) and his next publication, The Descent of Man (1871), about several "vestiges" in human anatomy that were left over from the course of evolution. These vestigial organs, Darwin argued, are evidence of evolution and represent a function that was once necessary for survival, but over time that function became either diminished or nonexistent.

The presence of an organ in one organism that resembles one found in another has led biologists to conclude that these two might have shared a common ancestor. Vestigial organs have demonstrated remarkably how species are related to one another, and has given solid ground for the idea of common descent to stand on. From common descent, it is predicted that organisms should retain these vestigial organs as structural remnants of lost functions. It is only because of macro-evolutionary theory, or evolution that takes place over very long periods of time, that these vestiges appear.

The term "vestigial organ" is often poorly defined, most commonly because someone has chosen a poor source to define the term. The Oxford English Dictionary (OED) defines vestigial organs as organs or structures remaining or surviving in a degenerate, atrophied, or imperfect condition or form. This is the accepted biological definition used in the theory of evolution.

In the never-ending search for scientific truth, hypotheses are proposed, evidence is found, and theories are formulated to describe and explain what is being observed in the world around us. The following are ten observations of vestigial organs whose presence have helped to flesh out the structure of the family tree that includes every living creature on our planet.

1. The human appendix
2. Male breast tissue and nipples
3. Fake sex in virgin whiptail lizards (vestigial behavior)
4. Sexual organs of dandelions
5. Wisdom teeth in humans
6. The blind fish Astyanax Mexicanus
7. The human tailbone (coccyx)
8. Erector pili and body hair
9. Hind leg bones in whales
10. The wings on flightless birds

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