Posted by PvM on June 8, 2006 10:19 PM
While Intelligent Design remains unable to explain much of anything in science, evolution has identified another mechanism. PZ Myer already discussed this example of Genetic Accommodation and I would like to use this as another example of the scientific relevancy of evolutionary science versus the scientific vacuity of Intelligent Design.
Here’s some very cool news: scientists have directly observed the evolution of a complex, polygenic, polyphenic trait by genetic assimilation and accommodation in the laboratory. This is important, because it is simultaneously yet another demonstration of the fact of evolution, and an exploration of mechanisms of evolution—showing that evolution is more sophisticated than changes in the coding sequences of individual genes spreading through a population, but is also a consequence of the accumulation of masked variation, synergistic interactions between different alleles and the environment, and perhaps most importantly, changes in gene regulation.
The paper in question and the commentary by Pennisi show how the effects of genetic mutations can remain masked until the environment reveals them. While genetic accomodation and polyphenism had been described, it had never been observed to evolve.
The genetic underpinnings of polyphenisms have long been a puzzle, notes Douglas Emlen, an evolutionary biologist at the University of Montana, Missoula. To examine how the tomato hornworm’s color-shifting may have arisen, Yuichiro Suzuki, a graduate student working with Frederik Nijhout at Duke University in Durham, North Carolina, turned to a tobacco hornworm mutant that is black rather than the normal green. Its mutation reduces secretion of juvenile hormone, which regulates skin coloring. This mutant strain, however, generates caterpillars with varying degrees of green if it is heat-shocked–briefly exposed to a very high temperature–at an early stage of development
Of course, I can already hear the ID crowd claim that this is just evidence of Intelligent Design. But remember that in this case natural processes of regularity and chance were responsible, not the supernatural processes logically required by Intelligent Design.
Allen MacNeill, who will be teaching a course at Cornell which explores the claims by Intelligent Design, presented his ideas on this concept. I applaud Allen for helping his students and readers understand how science explains these observations. Needless to say, Intelligent Design is unremarkably absent in providing an explanation, pathway or method.
Of course some ID activists have argued that ID is not in the business of providing such ‘pathetic’ pathways or methods.
As for your example, I’m not going to take the bait. You’re asking me to play a game: “Provide as much detail in terms of possible causal mechanisms for your ID position as I do for my Darwinian position.” ID is not a mechanistic theory, and it’s not ID’s task to match your pathetic level of detail in telling mechanistic stories. If ID is correct and an intelligence is responsible and indispensable for certain structures, then it makes no sense to try to ape your method of connecting the dots. True, there may be dots to be connected. But there may also be fundamental discontinuities, and with IC systems that is what ID is discovering.”
For those interested in reading the second reference provided by Allen, part of 5 Developmental Plasticity and the Origin of Species Differences–MARY JANE WEST-EBERHARD is reprinted in Systematics and the Origin of Species: On Ernst Mayr’s 100th Anniversary (2005). See especially page 76
Massimo Pigliucco has an interesting lecture on genetic assimilation arguing that genetic assimilation is both a developmental process and the subject of natural selection. See also Pigliucci’s paper PERSPECTIVE: GENETIC ASSIMILATION AND A POSSIBLE EVOLUTIONARY PARADOX: CAN MACROEVOLUTION SOMETIMES BE SO FAST AS TO PASS US BY? in Evolution: Vol. 57, No. 7, pp. 1455–1464.
Abstract.—The idea of genetic assimilation, that environmentally induced phenotypes may become genetically fixed and no longer require the original environmental stimulus, has had varied success through time in evolutionary biology research. Proposed by Waddington in the 1940s, it became an area of active empirical research mostly thanks to the efforts of its inventor and his collaborators. It was then attacked as of minor importance during the “hardening” of the neo-Darwinian synthesis and was relegated to a secondary role for decades. Recently, several papers have appeared, mostly independently of each other, to explore the likelihood of genetic assimilation as a biological phenomenon and its potential importance to our understanding of evolution. In this article we briefly trace the history of the concept and then discuss theoretical models that have newly employed genetic assimilation in a variety of contexts. We propose a typical scenario of evolution of genetic assimilation via an intermediate stage of phenotypic plasticity and present potential examples of the same. We also discuss a conceptual map of current and future lines of research aimed at exploring the actual relevance of genetic assimilation for evolutionary biology.