|MadSci Network: Evolution|
Noam, You are correct that mutations are indead random. What this means to a biologist is that there is no way to predict when, or where in a genome they will have an effect. Just because this is a random process does not mean that it operates without bounderies; a gene that codes for hemoglobin will not mutate into one that codes for insulin. Think of a single six-sided die, it is imposible to predict what number will come up when you throw that die, but you know it will be a number between 1 and 6. You also mentioned that some traits have no appearent effects. Again, you are correct, there are such things as neutral traits. What defines a trait as useful or not really is a measure of how it affects the ability of an organism to reproduce. This is a term evolutionary biologists call 'fitness'. A trait that causes early death would be considered quite detremental; one cannot reproduce once one is dead. So a lethal gene has a very low fitness rating. I cannot see how having six toes would affect weither or not a person can reproduce, so I would have to call six toes a neutral trait. However, when you think about evolution, you have to realize that conditions can change. If for some reason (albeit somewhat ridiculous) that human females somehow found men with six toes very attractive; so attractive that they would only mate with men with six toes, this would cause this particular mutation to become an advantage. It also passes that six toe gene into future generations, thus making it more common. Any good book of evolution will include examples of the 'founder effect' and of a 'population bottleneck'; these are two other ways that an uncommon trait may become common. As for other questions you asked. I assume by human ancestors, you mean apes. A better way to phase that is:"There is little difference between humans, apes, and the animals from which they evolved." When you consider the time scale upon which evolution works, it really hasn't been that long sence humans and apes diverged. Certainly not as long as apes diverged from other mammals, mammals from reptile-like creatures, and so on. The reason there are no "useless" organs is that all organs and tissues require energy to maintain. An organism that spends too much of its energy maintaining tissues that don't give much of a return probably isn't spending that energy reproducing. If you don't reproduce, you don't send your genes into the next generation, and therefore, those "useless" energy consuming organs, and the genes that regulate them, don't get passed down, causing them to be less and less common. Hope I was able to help. CHUCK
Try the links in the MadSci Library for more information on Evolution.