[Taxacom] Robust argument
mesibov at southcom.com.au
Sun Jun 28 00:25:11 CDT 2009
I couldn't agree more that the word 'genome' needs relaxing so that it isn't restricted to genes and gene inheritance, or alternatively that we use a word with a broader meaning, so that inheritance isn't restricted to genetic inheritance. There probably is such a word in the biological literature already. Anyone know it?
IMHO this is what Richard Pyle and others have done on TAXACOM a number of times, i.e. argued that genes are the only things passed down the evolutionary tree, therefore everything we can infer about organismal history is somehow inherent in the genome, and if we could only read the genome properly we'd have the whole evolutionary story.
All three clauses are untrue. This kind of reasoning had a chemical analogy in the 19th and early 20th century: organisms are only made of atoms and molecules, there's no vital force; therefore everything we can infer about how organisms work is inherent in atoms and molecules, and if we could only completely understand the chemistry we'd have the whole organismal story. Anyone still think that way?
Genes are not the only things passed down the evolutionary tree. Michael Heads and I have mentioned location. You can look as deep as you like into the genome, but you won't find the 'endemicity address' that locates a plant species on top of some mountain on Madagascar. That address is inherited. It's passed on to the next generation of seedlings by the current generation of seeding plants. Fuzziness in location as an inherited character is equivalent to variation in any gene-inherited character.
There are other non-genetic ways in which evolution is directed. Many are contained with the word 'co-evolution' - of parasites and their hosts, and of other tightly associated taxa. Think of a beetle which feeds on a particular plant, concentrates a particular metabolite from that plant, stores it in a special structure, then uses the material to defend its eggs against egg predators. You can find genetic traces of this separately in the beetle genome, the host plant genome and the predator genome. You think you can reconstruct this bit of evolutionary history from those genetic traces?
Conversely, there are inferences I can readily draw from fossil structures about the environments and evolutionary history of extinct taxa. I can't do that from the genomes of descendants, especially if there aren't any. Is this history irrelevant, because it isn't in the genome?
The only way in which the only-the-genome-contains-history fallacy can be sustained is for its proponents to claim that the only evolutionary history worth knowing is what can be deduced from relationships between the genomes of living forms. This is as circular as any reasoning can get.
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195
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