Posted by Adam on November 23, 1999, at 9:19:51
In reply to To anybody, posted by CC on November 23, 1999, at 1:02:51
> Can anyone give a mechanism for the "evolution" from one species to another? It seem to me that the accumulation of favorable or viable random mutations is unlikely from a mathematical point of view. Excuse me, I have to cast a demon out of my web browser.
Accumulation of favorable mutations isn't very likely, but given enough time, it makes a difference.
There really isn't much more to it than that. The cellular machinery that replicates DNA is pretty high
fidelity, but it's not perfect. And there are always mutations caused by chemicals or radiation. So
mutations are always occuring, and it is hypothesised at a fairly constant rate. Most of them are "silent"
in that they fall on a sequence of DNA that doesn't code for anything, or, because of the degeneracy of the
genetic code, the amino acid sequence of the final product isn't altered. Of the few that do make a real
difference, most of those are deleterius. Then, very rarely, there is a
mutation that confers a selective advantage. If that individual carrying the mutation reproduces, then
it gets handed down to a new generation, conferring a selective advantage on them, and so forth. When two
or more subgroups of a species are isolated somehow (usually by geography), their divergent accumulation
of genetic change (genetic drift) becomes so significant that they are no longer genetically compatible
from a reproductive standpoint. They are now genetically isolated from one another, and are now referred
to in scientific terminology as separate species. This is a bit of an oversimplification from a taxonomical
point of view, and is skewed toward sexual reproduction, but you get the idea. So you take the constant of
genetic change, plus a large number of individuals in a species, plus millions of years, plus physical
isolation of a subgroup, plus selective pressures, and you get the origin of species.
poster:Adam
thread:14368
URL: http://www.dr-bob.org/babble/19991123/msgs/15691.html