Expert: John Locke - 5/15/2007

Question
Dear John,

I am a Ph.D. Psychology student in Germany, and I am extremely interested in how biological evolution and adaptation processes work.

According to what I have read about "Selfish Gene Theory", adaptations are the phenotypic effects of genes, in order to maximize their representation in the future generations. According to this, an adaptation is maintained by selection if it promotes genetic survival directly or some subordinate goal that ultimately contributes to successful reproduction.

My questions are:

First of all, how much scientific evidence this theory has, and how is this theory viewed in the scientific community?

Can these phenotypic changes be inherited by next generations? And if so, how nucleic acids could be altered by external conditions?

Best regards,

Jeffrey  

Answer
Dear Jeffrey:

I realize that you have already received an answer saying that this is outside my expertise. Let me clarify a bit, as part of your question is well-established within the biology community, and part of it is still the subject of debate; I cannot speak to all aspects of the debate, and that is what is beyond my expertise. That does not come through with the standard rejection note you were given, and I want to give you a better answer than that.

There is universal concensus among the scientific community that adaptations are phenotypic effects of genes: natural selection always acts upon the phenotype of the organism (better camouflage, stronger muscles, etc.), and the kind of phenotypes that can be inherited depend upon genotype--there is more on this below. Also not in dispute is the idea that genetic survival is a criterion for measuring the success of an adaptation; ultimately, as you point out, genetic survival means surviving to reproduce. These ideas, of course, form the core of modern evolutionary biology, which is one of the best supported theories of all modern science. It is better characterized than modern theories of gravity, to take a common example.

What is unclear is to what extent the "gene-only" view of selection is accurate: at what level does natural selection primarily act--the phenotype, the organism, the gene, the genotype? Is the "gene-only" view, in which natural selection acts solely upon the gene, an accurate characterization? The debate may be broken down along two rough lines (as a psychology student, I'm sure you're familiar with the propensity to create dualities to help with cognitive organization): the gene-only view either reduces the process of selection too simplistically, or the gene-only view accurately characterizes genes as the units which are primarily passed along, not the overall organism or its phenotype.

Here's a brief summary of the gene-centered view of evolution:

"Genes do not present themselves naked to the scrutiny of natural selection, instead they present their phenotypic effects. (...) Differences in genes give rise to difference in these phenotypic differences. Natural selection acts on the phenotypic differences and thereby on genes. Thus genes come to be represented in successive generations in proportion to the selective value of their phenotypic effects."

Here's a point that typically encompasses the objection to this view:

"I do not deny that natural selection has helped us to explain phenomena at scales very distant from individual organisms, from the behavior of an ant colony to the survival of a redwood forest. But selection cannot suffice as a full explanation for many aspects of evolution; for other types and styles of causes become relevant, or even prevalent, in domains both far above and far below the traditional Darwinian locus of the organism."

As to the scientific consensus on this, I am regrettably unable to speak to that. There is some push to view the gene not as the unit of selection, per se, but instead as teh unit of evolution--that is, the gene ultimately determines how organisms evolve over time, though it is not the final controller of individual selection. Perhaps the leading proponent of the gene-centered view of evolution is zoologist Richard Dawkins; perhaps the leading critic was the paleontologist Stephen Jay Gould.

As to your second question: phenotypic changes that do not have a genotypic origin do not get passed from generation to generation. This theory of evolution--the inheritance of acquired characteristics--was proposed by Jean-Baptiste Lamarck before Darwin ever took his famous voyage on the HMS Beagle. In a sense, it represented a good effort on Lamarck's part to explain the wide variation seen in the natural world, though it is not at all correct, for a number of reasons, the least of which is perhaps the simplest: only genetic material gets passed from generation to generation (in humans, for example, only the 23 chromosomes carried by the sperm and the 23 carried by the egg go on to form the embryo).

That said, it is possible for changes in environment to affect the genotype of an organism, which results in a distinct genome that can be passed on to the next generation. This would have to occur fairly early in the embryonic stage, when the embryo consists of only a small number of undifferentiated cells; once further differentiation takes place, changes to the somatic cells would not also necessarily show up in the gamete cells. It would be possible to affect the cells for neural development, for instance, without affecting the cells that will go onto form sperm or oocytes.