To: All Msg #23, Apr0393 11:02AM Subject: theories of abrupt appearance Recently, a 'theor

From:    Chris Colby                            
To:      All                                    Msg #23, Apr-03-93 11:02AM
Subject: theories of abrupt appearance

Organization: animal -- coelomate -- deuterostome
From: colby@bu-bio.bu.edu (Chris Colby)
Message-ID: <113910@bu.edu>
Newsgroups: talk.origins

Recently, a 'theory of abrupt appearance' has been offered on 
talk.origins. I would like to make a few comments about it and
ask a couple questions.

To begin, I'd like to point out that theories of abrupt appearance
are nothing new to biology. Prior to Pasteur, people thought
'lowly organisms' sprung into existence spontaneously. More recently,
two theories of abrupt appearance have been written by evolutionary
biologists. In the '40s, Goldschmidt posited that large phenotypic
changes occurred by 'systemic mutations' -- i.e. large mutants, or
'hopeful monsters' were occasionally formed and very rarely they
thrived. He saw the need to invoke this mechanism because he saw
that in the organisms he studied (moths, I believe -- don't quote
me), characters that varied between species were not the characters
that varied within species. Although genes have been found that can
produce large phenotypic effects (homeobox genes), his theory is
almost completely discredited. (Although, I thought that some legit
entomologists believe that the transition from 4 winged flies to
2 winged flies may have been via macromutation. The reverse occurs
in _melanogaster_ (the ultrabithorax mutant).)

Much more recently, Gould and Eldredge have authored punctuated
equilibria (or 'punk eek' or much less charitably 'evolution by
jerks'). This is another theory that states new species appear
abruptly (at least in the fossil record). The gist of their theory
is that transitions happen in isolated locales, then the newly
speciated population may displace the old one. Instant transitions
in the fossil record are the result of replacement by migration.
(They also claim that phenotypic change may occur quickly (in
geologic time) so that transitional forms are restricted both in
space and time.)

Both of these species address two specific topics, neither of which
the 'theory of abrupt appearance' appears to: tempo and mode.

Other posters have quickly picked up upon the lack of specificity in
the theory with regard to time frame. I'll simply restate their
question. How fast is abrupt? In Goldschmidt's theory 'abrupt' was
within one generation. A hopeful monster was born and it could
then begin increasing in population size if it happened to be well
adapted (I'm not sure how it would find a mate -- the library has
Goldschmidt, maybe I'll check it out if there is interest.) In
punk eek abrupt transitions occur instantaneously in geologic time.

But, these are artifacts of sampling. Unless the paleontologist is
digging at the spot the population transformed, he/she won't find
any transitional fossils. In most locales, the abrupt change in species 
is dues to species B (which evolved somewhere else) invading the 
territory of species A - _not_ species B evolving from species A.
B may have evolved from an population of A, of course. Here's
a brief cartoon to illustrate. Imagine the letters below are fossils;
going down vertically would be older rocks. The horizontal is
different geographic locations.

B     B       B       B       B       B       B       A
B     B       B       B       A       A       A       A
B     A       A       A       A       A       A       A
A3    A       A       A       A       A       A       A
A2    A       A       A       A       A       A       A
A1    A       A       A       A       A       A       A
A     A       A       A       A       A       A       A

B evolved from A in the leftmost column here; later it
expanded its range at the expense of A. In all the middle
columns, the A to B transition is due to migration, not evolution.

The second question is mode. This is, I think, a much more
important question to the most recent 'abrupt appearance'
theory. In both the hopeful monster and punk eek theories --
new species came from old species. The question that is
begging to be asked is -- where do species come from in
the 'theory of abrupt appearance'? (And, of course, what
evidence do you have for your proposed mechanism of species
formation (whatever it is)?)

Does Bird's theory answer these questions? (I suspect not.)
Are there any predictions Bird's theory makes that are at
odd with evolutionary biology? (Again, I suspect the 'theory'
will prove to be squishy enough to accomodate any observation
-- i.e. it won't really be a theory at all.)

Chris Colby   ---      email: colby@bu-bio.bu.edu     ---
"'My boy,' he said, 'you are descended from a long line of determined,
resourceful, microscopic tadpoles--champions every one.'"
      --Kurt Vonnegut from "Galapagos"