Re: new method of evolutionary change

David Campbell (bivalve@isis.unc.edu)
Mon, 14 Dec 1998 14:15:14 -0400

>You can get "abrupt change" in fruitflies by mutations. You can get
>abrupt change in your computer by hitting it with a hammer.
>
>The question is how you build up genetic information, or the software in
>Windows 98.

I wonder whether Windows 98 is all that good an example of an organized
product.

More seriously, a mutation is a production of new genetic information. In
combination with the existing genetic framework, it may have an
insignificant effect (in most cases) or, more rarely, it may have a
significant impact, either positive or negative or mixed. If the mutation
does not prevent reproduction, then the level of competition would
determine whether the mutant is able to survive and pass along its genes.
In multicellular, diploid or polyploid individuals, the mutation is along
with the normal version of the gene and so both the individual and the
species have one more kind of genetic information.

A more dramatic way to build up genetic information is to duplicate part of
the genome. This can happen by unequal crossing over during meiosis or by
hybridization (common in plants, rarer in animals), among other methods.
As a result, the organism has extra copies of genes. As long as one stays
functional, mutations in another copy may provide novel functions.

Processes such as these seem adequate at least for the genetic changes
necessary to go from a primitive genetic framework to the modern genetic
diversity of organisms. There is some evidence for these processes
occuring in the development of life prior to the full development of the
DNA-RNA-protein system that is basic to all modern organisms, as some of
the transfer RNA genes are mutated copies of each other.

Complex molecular systems can be built up by mutations in various ways.
One is to simply add steps onto an existing chain. This would probably
have been particularly important in the early stages of the creation of
life, when a proto-organism that became able to start a process with a new
raw material would have had a large competitive margin relative to those
all relying on the same thing. Another way is to combine existing pieces
into a larger system. The extreme flexibility of enzyme design also helps
build complex systems. Enzymes that are structurally very different may do
the same thing, and enzymes that are almost identical may do very different
things. Thus, the mutations required to achieve a given result may not be
as many as it would seem from such analogies as trying to write Shakespeare
by random typing.

However, the initial development of life remains poorly studied and poorly
known. This reflects both a lack of knowledge (we are still learning how
modern molecular systems work) and a lack of interest (both financial and
humanitarian factors favor biochemistry focused on medical, agricultural,
or industrial applications rather than evolutionary ones, and often
biochemists have a very weak background in organismal and evolutionary
biology).

David Campbell

"Old Seashells"

Department of Geosciences
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315
USA

919-962-0685
FAX 919-966-4519

"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug