DOG DAZE:

Repeat after me: Evidence that evolutionary change is not always a smooth process (The Economist, Dec 16th 2004)

ONE of the most acrimonious disputes in biology is between those who believe that evolutionary change is a smooth and gradual process and those who think it happens suddenly—evolution by creeps versus evolution by jerks, as some of the protagonists unkindly put it. The gradualist model tends to be favoured by those who study things that are still alive, while the punctuated-equilibrium model, as the sudden-transition way of looking at the world is known in the trade, finds its support among those who study fossils, and who feel that the evidence from the rocks favours their view.

Now, though, the jerks have some support from two researchers who are studying still-living organisms. John Fondon and Harold Garner work at the University of Texas Southwestern Medical Centre, in Dallas. They have been looking at the genetics of dog breeds. And they have found a mechanism of genetic change that could help to explain punctuated equilibria.

The traditional, creeping-change model of evolution has natural selection working on the genes themselves. Genes carry the blueprints for proteins, the molecules that do most of the hard biochemical work in living creatures. Change the blueprint and you change the protein's function. Most changes will be damaging. But occasionally, by chance, one will be advantageous, and will spread through the population.

Each such advantageous protein change, however, is likely to have only a small effect. So the creeps cannot see how sudden shifts can happen. But the jerks have come up with a possibility—that the pertinent changes are happening not in the genes themselves, but in the bits of DNA that regulate gene expression. These are places near genes at which special proteins that act as gene-switches can attach themselves in order to stimulate or suppress the activity of a gene. Changing the regulatory DNA leaves the proteins derived from a gene unaltered. They therefore continue to work properly. But the amount produced, or the time during development at which they are produced, is different. That could result in large changes in morphology, of the sort that would be obvious in the fossil record in the way that subtle biochemical shifts are not.

In fairness to the blind adherents of Darwinism, who will be understandably upset at being trumped by jerks, it should be noted that there's nothing sillier than studying the effects of "natural" selection on a species we domesticated tens of thousands of years ago and have subjected to intense inteligent design ever since.

Posted by Orrin Judd at December 22, 2004 11:35 PM