Claim CB710:
Evolution predicts that different kinds of organisms should have different
genetic programs, but the genes responsible for major effects early in
development are very similar across diverse phyla. For example, the gene
distal-less gives rise to limbs in several different phyla, but the
limbs themselves are not structurally or evolutionarily homologous.
Source:
Wells, Jonathan. 2000. Icons of Evolution, Washington DC: Regnery
Publishing Inc., pp. 74-76.
Response:
- Wells's observation is quite in accord with what evolution predicts.
Genes responsible for early developmental effects should not be
expected to change greatly because small changes early in development
produce large changes later, and those large changes are likely to be
damaging. It makes more sense that the genes to change would be the
ones that modify and regulate the early developmental genes. Thus, the
genes that cause a limb to grow would be conserved, but many of the
genes that regulate its form would not.
- There are significant differences between phyla, too. Although any
given HOX gene (the genes that determine much of an animal's basic body
plan) may be very similar between phyla, different phyla differ in
which HOX genes they carry and in how many copies of each they have
(Carroll 1997).
Further Reading:
Carroll, Robert L. 1997. Patterns and Processes of Vertebrate
Evolution, Cambridge and New York: Cambridge University Press. See
especially chap. 10. (technical)
created 2001-3-31
