Homologous structures - Homologous structures genes and...

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Homologous structures, genes, and developmental pathways Summary of problems with claim: Similarities in developmental pathways are one of several criteria scientists use for "homology." Presenting it as the sole criterion is incorrect. Full discussion: As noted elsewhere, the authors of Explore Evolution first create a "strawman" in generating their "Case For". Specifically, for anatomical homology, the authors draw the following conclusion: two different animals can be said to have "homologous structures because they were built by homologous genes" through "developmental pathways" that are homologous (p. 41). To add support to their conclusion, the authors quote two "neo-Darwinian biologists" Alfred Romer and Thomas Parsons who believed "[T]he identity between homologues is based upon the identity or similarity of the developmental properties…[and] hereditary units, the genes" ( EE , p. 41). The source cited is a textbook originally published in 1949, with the latest edition published in 1977. Biologists’ understanding of genes and development has advanced dramatically in the past 30 years, and it is irresponsible of the authors to rest their discussion on such an outdated source. Closer examination of the "Case For" reveals many problems with assuming the above conclusion. Darwin did not know about genes and developmental pathways. Darwin’s theory of common descent and thoughts regarding homologous structures make no predictions about what we expect to find at the developmental and genetic level. Numerous evolutionary biologists have addressed this assumption. Wagner (1988) stated that there is no simple congruence between anatomical characters and genotypes and hypothesized that only those features of the developmental system that cause a restriction in the possible phenotypic consequences of genetic variation (i.e., developmental constraints) are important. Even de Beer (1951), quoted by the
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