I agree that mutation is not the only source of variation that can
lead to evolution but it certainly is a very important source. Even in
your example of horizontal gene flow from bacteria to humans, it is
likely that some of those genes and alleles arose via mutation prior
to the horizontal transfer. The leading proponent of horizontal
transfer, Carl Woese of the University of Illinois, believes that
three cell types, bacteria, eukaryote and archaea, arose independently
and underwent a lot of horizontal transfers early in evolution:
http://www.usatoday.com/news/healths...-evolution.htm

Even with three independent origins of cells, there would have been
little genetic variation to begin with. Thus, wouldn't the greater
part of the huge number of genes and alleles present today have arisen
by mutation over the 3-4 billion years after the origin of life?

David R. Hershey



"John Margetts" wrote in message ...
The human genome project has shown that some human genes originated in
bacteria and have been passed to humans from the bacteria by horizontal
transfer.

There is no reason to believe that this is unique to humans and has almost
certainly happened to many other organisms in other kingdoms as well as
humans.

This is evolutionary, but does not involve the mutation of any alleles,
merely the addition of new (for that organism) alleles.

I am not, of course, saying that mutations do not happen, just that there
are other ways for the genome of any organism to change possibly leading to
selection and thus evolution.

John

"Don't ask me what I think of you, I might not give the answer you want me
to, Oh well." - Peter Green

"David Hershey" wrote in message
om...
If chance mutations don't give rise to new alleles in plant species,
then how do they arise? Many alleles do not code for "normal" or
functional proteins. The explanation is that the abnormal alleles
arose via mutations in the existing normal allele.

snip