Very Vestigial

Vestigial parts, sometimes called vestigial organs even though some parts are not actual organs, are things that are part of a body, but no longer have a definite purpose or at least no longer used for the purpose for which they were originally intended.  Even though penguins have wings and use them to swim, they are considered by most to be vestigial because they are no longer used for their original purpose - flight.  Emus and ostriches, the tallest birds in the world, are also birds that have wings but no longer fly.  They don't normally swim (although emus can if they have to), but they do use their wings for balance and mating displays, and ostriches also use them to help regulate body heat.

Emu   Source:  Wikipedia

Other flightless birds include kiwis, rheas and cassowaries.

Cassowary    Source:  Wikipedia

Besides flightless birds there are also some species of weevils and other beetles that have wings but do not fly.

Some animals have what could be called vestigial eyes, because they no longer use them to see.  Blind mole rats live underground and their eyes are actually covered with a layer of skin.

Source:  Wikipedia

Cave fish and cave salamanders, as their name implies, live in dark caves and no longer need to see.  Some cave fish can detect light and dark, but others actually have no eyes at all.

Source:  Wikipedia

Other adaptations to their surroundings include loss of pigmentation (some are actually translucent) and a body clock that does not respond to light.

Humans also have vestigial parts such as wisdom teeth or third molars. Normally these teeth never erupt from the gum and are 'leftovers' from ancestors that needed these teeth for chewing and grinding plant material.  However, about one third of all adults, as in my case, have either malformed or impacted teeth that need to be removed.  Unless there's a problem, most people may not even realize they have these teeth.

Another human vestigial part is the coccyx, also known as the tail bone, which it literally is - the remains of the base of a tail.  The coccyx consists of four fused vertebrae found at the base of the spine, exactly where most mammals and many other primates have external tails protruding from the back/  However, the coccyx seems to have no purpose as it is not used in either sitting or walking.  Neither is it used for grasping or balance which is what tails are normally used for.  Humans and great apes are some of the only vertebrates that don't have tails as adults. 

Appendix, tonsils, and redundant veins could also be considered vestigial, although recent studies have shown that perhaps they are not as 'useless' as originally thought.  Perhaps the smallest vestigial human part is DNA which is considered 'junk' DNA or DNA that as far as we know now seems to have no purpose.

Perhaps the most interesting vestigial 'part' is actually a behavior or reflex known as piloerection.  Have you ever thought about why we have 'goose bumps'?  Have you ever watched the hair on your cat or dog puff up in moments of stress or defense?  It was also a function of our human ancestors - a means of raising the fur on the body to make it look larger and scare away predators.  When it's cold, this action also allows air to be trapped between the hair of the fur to provide insulation.

Source:  Wikipedia

All these examples show adaptations to changing environments and evidence for the evolutionary process.

For more on human evolution, check out 'Your Inner Fish' on my Book Recommendations page.