Between beanbag genetics and natural selection

Abstract

The encounter between the Darwinian theory of evolution and Mendelism could be resolved only when reductionist tools could be applied to the analysis of complex systems. The instrumental reductionist interpretation of the hereditary basis of continuously varying traits provided mathematical tools which eventually allowed the construction of the ‘Modern Synthesis’ of the theory of evolution. When genotypic as well as environmental variance allow the isolation of parts of the system, it is possible to apply Mendelian reductionism, that is , to treat the phenotypic trait as if ti causally determined by discrete “genes for” the trait. howeverm such a “beanbag genetics” approach obscures the system's eye-view. The concept of heritability, defined as the proportion of the total phenotypic variance due to (additive) hereditary variation, asserts that genetic elements have discrete effects; but by relating to the genotypic variance, it avoids the trap of reffering to “genes for” characters. Variation in relative reproductive success is the phenotypic “trait” of significance for Darwinian evolution, and fitness is its genotypic component. Most traits that contribute to reproductive success are due to the effects of many loci that causally contribute to the adaptive value of those traits. by establishing a causal relationship between the heritability of traits and reproductive success the apparent tautology of the definition of fitness through reproductive success is avoided, without the need to turn to simplistic and misleading concepts, such as the “genes for” the traits.