ava, it depends. If there is no longer evolutionary pressure for something, it may become vetigial (like prehensile toes or tails), but rarely disappear, at least in the comparatively short term. On the other hand, I remember the answer my genetics professor gave when someone asked why men have nipples: “Why not?” There is no evolutionary pressure for it to disappear; it doesn’t affect reproductive fitness one way or the other.
I think Cecil addressed this in one of this columns, but I can’t find which one.
Once something no longer is used, it does not simply disappear. However, a mutation might cause it to not develop. Since it is not being used, the animal (or plant) is not harmed by its absence. (There even may be a slight advantage in not expending the energy to build or maintain it.) The mutation is then passed to the next generation. Depending on whether the mutation is dominant or recessive and whether or not it provides a strong advantage, the mutation may begin to percolate through the genes of the whole group in successive generations, eventually leading to its disappearance from the species.
It is quite possible that something “useless” could survive for quite a long time, provided the genetic code was not subject to a lot of mutation.
The loss or reduction of a structure can be beneficial to an organism if, by its (the structure’s) absence, a selective advantage is bestowed upon that organism. This typically would occur when some other structure takes on the “job” of the older version, or when that function becomes obsolete, given the current environment; at that point, the structure becomes selectively neutral, and morphological changes can (theoritically) occur in any direction. Thus, over time, absent any reason to select for any given size, a structure could simply be reduced through random fluctuations (or, it could acquire a whole new function, thereby creating an entirely different evolutionary pathway for that organism’s lineage). Often, however, as noted by Telemark, resources within a developing organism can be used better elsewhere and less “effort” is put into developing a structure that no longer serves any useful function. Thus, it becomes vestigial: the genes to make the structure are still active, but there is less developmental effort put into making it “full-fledged”.
It could also be a case of direct selection: if the current environment favors a smaller version of a structure than the current average, there might be an active pressure for the structure to reduce in size.
For human pinky toes and appendices, however, I would say your teacher was engaging in unfounded speculation: evolution does not predict the future, it explains the past. Just as no historian can reliably tell us the state of the world 100 years from now, no evolutionary biologist can tell you what features we may or may not lose in the distant future. We (a general “we” - I’m no evolutionary biologist) can certainly point to trends, but evolutionary trends are statistical, not absolutes.
Although your teacher was smoking crack to think that he/she could predict the future path(s) of evolution, I can think of a reason why pinky toes might be selected against.
Women born without pinky toes can fit into narrower shoes. Narrower shoes are fashionable, and therefore sexy and will increase the woman’s chances of attracting a mate, with whom she’ll have lots of little pinky-toe-less babies. (I seem to remember it was trendy at one point for women to get their pinky toes removed so that they could fit into narrower shoes. Ick.)
Pubic and armpit hair seems to serve a sexual function as well. It retains the scents and pheromones generated by your body. (Although it’s difficult for me to imagine anybody but a fetishist saying, “Hey, baby, let me sniff your armpit hair.”)
Someone at Belief.net posted a link to this site a while back as an argument against evolution or atheism(one of the two).I and a few others actually took the time to copy/paste and address each point in turn and , as usual the fundie-creationist ducked out without aknowledging that they had their asses handed to them or bothering to try and answer any of our points/counterpoints.
DO not apologise for that site is lucky to be wrothy of mockery it is so bad.