*Modern synthesis problem?

James Lyons-Weiler LYONSW at UCONNVM.bitnet
Fri Mar 4 08:41:38 EST 1994

Jeff Smith writes:

To: bioforum at net.bio.net
From: jsmith at mondrian.CSUFresno.EDU (Jeff Smith)
Subject: MODERN SYNTHESIS problem???
Sender: Jeff.Smith at net.bio.net
Date: Thu, 3 Mar 1994 23:46:03 GMT

I have a question about Modern Synthesis that I need help in
understanding.  I am taking an Evolution class this semester and were
talking about the idea of Modern Synthesis.  The fifth statement (in
the book we are using) says this: "The continued accumulation fo
genetic differences, under the principal guiding force of natural
selection, results in new taxa above the species level by the same
processes that produce new species." (Process and Pattern in Evolution
by Charlotte Avers. 1989).

What exactly does that mean?  What is meant by "new taxa"?  Does it
suggest that new species that evolve from other species must be higher
up on the "ladder"?  I guess the thing that is most confusing to me is
the term "new taxa".  I don't really understand what is trying to be
said by using the term new taxa.

Can anyone offer help?  I am open to your ideas and insights into

Jeff -

Your confusion is well understood.  There are (at least) two ways to interpret
the statement (neither of which, by the way, require a "ladder" or primitive-
advanced type arguments).  The first way would be to intepret the statment
as saying that natrual selection can act upon groups of organisms above the
level of the individual.  Classical natural selection works through the
differential survival and reproduction of INDIVIDUALS, while the effects
of that selection are manifested in changes in the properties of POPULATIONS.

Some people think that natural selection can act through the differential
survival of groups (e.g., populations, species, genera, families).  I am
not one of them.  Any process of so-called selection upon groups can be
explained more easily as the RESULT of natural selection removing or

Surprisingly, the statement can also be taken to mean the exact opposite of
what I have outlined - that the generation of what systematists would call
a new genus, family, or kingdom of organisms depends soley on the forces of
natural selection as we already understand them to work - upon individuals -
and that we do not require any new forces to explain diversification of
higher (FAMILY > GENUS > SPECIES, not ADVANCED > PRIMITIVE (see the difference?
)) taxa.  Another way to communicate more clearly about his kind of thing is
to talk about deep vs. shallow phylogenies; species - level differences
are typically shallow (in evolutionary terms, usually in time as well),
while family - level comparisions are typically deeper in history.

Good question!


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