> >Take cattle for example, as they have been domesticated in massive
> >amounts for millennia. They have changed physically in size,
shape,
> >color & etc., slightly due to selective breeding, but they are all
> >still are cloven hoofed furry animals that moo. Their udders
> >haven't begun to relocate nor have they begun development of canine
> >teeth (or any meaningful upper front teeth for that matter).
> >They've always been ruminants with multiple stomachs and it doesn't
> >look like that will ever change. No changes that would
distinguish
> >them as another or new developing species have occurred.
Since these occurred largely through human selection it is unlikely
that anyone would have selected for cows with canine teeth. This would
be counter productive since it would interfere with their ability to
graze so weight gain and milk production would be adversely affected
:-)
On a more serious note human selection of domestic plants and animals
only shows the potential for "natural selection" but in most cases
does not touch upon events similar to speciation. There are good
reasons why one would not expect to see massive changes in a short
period of time. The genetic systems that regulate and support
development are complex and changes that would result in strong
differences, genus or family level, would probably act as leathals in
most cases. Consider also that these genetic systems cannot be
assessed in isolation for the environment in which they occur. There's
been a lot of fine tuning that keeps and organism adapted to it's
environment.
A somewhat different circumstance exists during periods of
catastrophic environmental change. With the loss of many competitors,
the competitive restraints are relaxed. Another interesting issues
revolves around the origin of major lineages (family to order levels).
These may well have developed fairly rapidly early in evolutionary
history when variations of regulatory gene complexes with relatively
subtle differences at the time they split off, and diverged greatly as
time went on.
Phil Bunch
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