Name: Matt D Carter
Why do organisms mutate?
Not sure if you mean "how" or "how come." If the second, then it's
because this ensures a variation in the characteristics of the offspring.
Each new generation of cheetahs includes a few who can run faster (but need
to sleep more, say) and a few who can't run as fast (but who can go longer
without food), and a lot who are pretty much the same as their parents.
Then the environment does its job, and whoever isn't good enough at getting
food dies and has no kids. The genes for the abilities that don't do the
job get deleted from the species, and the average ability of the cheetah to
get food rises. By and by they become real good at it. You still need to
preserve the ability to adapt to the environment at this stage because the
environment changes. Evolution is what makes species improve, and the two
key parts of it are mutation and natural selection (the deletion process;
it's not "natural" in the sense of "normal" but "natural" in the sense of
"done by Nature.")
Now if you mean "how," then the answer I think is usually assumed to be
deliberate errors in duplicating DNA by the cell. The machinery for
copying DNA is just set up so that every now and then it copies the recipe
for a new cell as "1 egg and 1 eye of newt" instead of "1 egg and 1
teaspoon baking soda." X-rays and certain chemicals increase the rate of
mutation, but I'm not sure this is significant in general.
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Update: June 2012