GC Williams and Socrates

Thought I’d pull this passage out of GC Williams’s “Adaptation and Natural selection“. I was looking for it the other day, as I’m considering using it in my Evolution class, and couldn’t find it easily via google.

“Natural selection of phenotypes cannot in itself produce cumulative change, because phenotypes are extremely temporary manifestations. They are the result of interactions between genotype and environment that produces what we recognize as an individual. Such an individual consists of genotypic information and information recorded since conception. Socrates consisted of the genes his parents gave him, the experiences they and his environment later provided, and the growth a development mediated by numerous meals. For all I know, he may have been very successful in the evolutionary sense of leaving numerous offspring. His phenotype, nevertheless, was utterly destroyed by the hemlock and has never since been duplicated. If the hemlock had not killed him, something else soon would have. So however natural selection may have been acting on Greek phenotypes in the forth century B.C., it did not of itself produce any cumulative effect.

The same argument holds also for genotypes. With Socrates’ death, not only did his phenotype disappear, but also his genotype.[...] The loss of Socrates’ genotype is not assuaged by any consideration of how prolifically he may have reproduced. Socrates’ genes may be with us yet, but not his genotype, because meiosis and recombination destroy genotypes as surely as death.”

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3 Responses to GC Williams and Socrates

  1. There doesn’t seem to be much “type” in Williams’s idea of “genotype” or “phenotype”.

    He seems to be referring to Socrates’s full genome/physical manifestation, rather than some subset which might constitute of a “type” that others have.

    (of course I couldn’t resist commenting on something about evolution and Socrates together!)

  2. cooplab says:

    I guess I too would class an organism’s genotype as its entire genome, and would specify the “genotype at a set of loci” if I wanted something smaller (or drop the set of loci, if it was obviously implied). But I’m sure folks have given it a lot more thought than I have.

    Shall we have coffee sometime soon?

    • I thought I’d remembered Richard Lewontin writing an article on the genotype/phenotype distinction. I couldn’t find the one I remembered (it was in a book), but I found this other one he’d written for the Standford Encyclopedia of Philosophy:

      http://plato.stanford.edu/entries/genotype-phenotype/

      In a sense, he agrees with both of us:

      “Real organisms are characterized by great variation one from another. Typically, individual members of any species differ in very large numbers of nucleotides that make up their DNA. In humans there are 3 million nucleotide differences on the average between any two people taken at random. Even very closely related individuals have many genetic differences. With the exception of twins or individuals cloned from the same parent, no two organisms have identical genomes. Moreover there is some ambiguity in assignment of an individual to a genotype, because many mutations occur in cells during the process of growth and development so that all the cells in the body do not contain identical genomes. Even asexually single-celled organisms like bacteria that are reproduced by the division of the parental cell differ in their genomes because mutations of DNA are sufficiently common that at least one of the nucleotides that constitute their DNA will have undergone a spontaneous change during cell division. Thus genotypes are classes with only a single member. Moreover, even cloned individuals or identical twins , although identical in genotype, will differ from each other in phenotype because of variations in their developmental environments. Thus, phenotypes are also classes with only a single member.”

      but:

      “In practice genotypic and phenotypic descriptions are not total but partial, restricted to some subset of the characteristics of the organism that is regarded as relevant for a particular explanatory or experimental purpose. In the delimitation of partial phenotypic and genotypic descriptions two decisions must be made. First, a particular aspect of the total phenotype is chosen for description, say the rate of production of melanin pigment from the biochemical processing of small molecules by enzymes, which then dictates that the genes that code for the enzyme proteins involved in the reaction are part of the partial genotype of interest. Second, a decision must be made about what set of phenotypes and genotypes are to be regarded as indistinguishable and so are to be included in the definitions of the partial genotypic and phenotypic classes. In the case of melanin pigmentation there is a continuous distribution of the trait from very light to very dark color because of environmental variations and because of small variations from individual to individual in the actual rates of enzymatic activity. What range of melanin deposition will be regarded as belonging to the same phenotypic class? The necessity of establishing boundaries for phenotypic classes arises because, although pigment intensity is a continuous variable, genotypes are, by their nature, discrete classes. So the problem of phenotypic class boundaries must be addressed.”

      In any case, yes, let’s get coffee soon. I’ll send you an email in a moment.

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