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Re: Triceratops sprawl

In a message dated 96-02-03 10:36:30 EST, Robert.J.Meyerson@uwrf.edu (Rob
Meyerson) writes:

>It may not have a purpose, but once an evolutionary trend is started, things
>tend to progress along that line till the evolutionary momentum is stilled.
>For other examples, see the evolution of legs from fins and whale evolution
>in general.

"Evolutionary momentum" is an artifact of focusing on one single interesting
lineage. Here's a simple picture of how I see evolution working:

Over the course of a few hundred thousand years, species A gives rise to
several daughter species, say B1, B2, B3, B4. Only one of them, say B1,
survives long enough to give rise to more daughter species, say C1, C2, C3,
C4. Only one of them, say C1, survives long enough to give rise to more
daughter species, say D1, D2, D3, D4. Etc., through, say, Z1, Z2, Z3, Z4.
Inconveniently but quite reasonably, of the daughter species that evolve at
any time, only the #1 species (if any at all) survives long enough to leave
any kind of a fossil record. The "interesting" lineage becomes the one that
runs from A through Z1, and by singling it out and ignoring/omitting the
others, that lineage gains the appearance of an "evolutionary trend" from A
to Z1.

But there's really no trend, no "evolutionary momentum," just differential
survival of lineages coupled with our not unreasonable tendency to study the
lineages we can actually see in the fossil record.