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Cambrian Explosion

Tom Holroyd tomh at BAMBI.CCS.FAU.EDU
Thu Feb 23 22:34:30 EST 1995

I always thought that the explanation for the Cambrian Explosion
was the emergence of sex.  Naturally, this is because I had never
given it much further thought. :-)

Work in artificial evolution using computers (GP and GA) has shown
that crossover is a more important mechanism for variation than
simple point mutations.  If pre-Cambrian organisms simply replicated
themselves, then the emergence of sexual reproduction could have
ushered in a large increase in variation - what we now call the
Cambrian Explosion.

Senapathy's theory suggests an even more dramatic mechanism than
the shuffling of genes via sex.  As I understand it, sets of genes
became capable of spontaneous self-assembly into genomes, some of
which produced viable organisms.  Instead of crossover between
similar genomes, there was wholesale re-creation of the genome
from a large set of genes each generation.

I like the idea of self-assembly.  But, something had to be making
the genes that could then self-assemble.  I can imagine a large
metabolic network with ill-defined boundaries producing genes by
replication.  But this would be long before the emergence of
separate organisms, I would think.  Perhaps the organisms excreted
genetic material which then recombined. :-)

I think Senapathy underestimates the amount of variation that is
possible with ordinary Darwinian evolution.  Computer simulations
using only mutation would, indeed, not produce the required amount,
but as stated earlier, crossover is a more potent force.  Senapathy's
theory might be relevant earlier, before the emergence of cells, when
autocatalytic metabolic networks used genes for regulatory functions.
Exchange of genetic material between domains of this network would
have amounted to a sort of 'super-sex'.  I would thus not discount the
possibility of self-organization at the level of the genome.

Tom Holroyd
Program in Complex Systems and the Brain Sciences	   The basis of
Florida Atlantic University, Boca Raton, FL 33431 USA	   stability is
tomh at bambi.ccs.fau.edu					   instability.
The 9th Amendment of the U.S. Constitution:
"The enumeration in the Constitution, of certain rights, shall not be
construed to deny or disparage others retained by the people."

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