MadSci Network: Evolution

Re: Speciation

Date: Thu Aug 20 13:07:01 1998
Posted By: Mike Conrad, Post-doc/Fellow, Microbiology, UNC
Area of science: Evolution
ID: 900859956.Ev

Let's see now, just answering off the top of my head (no references
except my Webster's New World)

In biological classification, a species is a division of a genus.  A 
working definition of a species is a group of plants or animals that
have a high degree of similarity and generally interbreed with

Take dogs (canis familiaris) or cats (felis catus).  Dogs are thought of
as being their own species.  They can interbreed with wolves, but that
doesn't happen usually in nature.  So the interbreeding thing isn't
absolute.  And just a few mutations will not a species make.  But when the
chromosomes are of different number or are different enough, when the
egg meets the sperm, the inability of the chromosomes to pair can prevent
a viable offspring from forming.  Or, the offspring is viable but sterile,
for example horses and donkeys make mules, which are sterile.  Lions and tigers 
make ligers and tiglions, depending on which is the father, and I think one of 
those combinations is fertile and the other is sterile.

Have we ever seen a new species arise?

Well, the development of the mamalian species occurred over tens of
millions of years.  There was plenty of time for geographic isolation to 
result in divergence through selection of variants, reproductive isolation
and then speciation.  The divergence of birds on the Galapagos clued
Darwin in to the idea that natural selection generates new species.
Actually this evolution happened rather "quickly".  The Galapagos are
quite "young" volcanic islands being only several million years old.  But
that's still millions!

But wait a minute.  Dogs developed from wolves coexisting with man and
then being domesticated.  This happened in the last ten
thousand years or so.  So there's a new species that people have actually
witnessed the creation of.  And cats are a new species that was developed
by man in Egypt also about ten thousand years ago from some wild ancestor.
People did that too.  So I guess you can say we've seen the development of
these new species within human time.   

I think there are about a million and a half different species named and
most of those are insects and most of the insects are beetles.  I've heard
that beetles get so specialized that even different individual trees in
the tropics can have their own species of beetles.  That's pretty extreme
if you ask me, but that being the case, there should be many recent
beetle species.  

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