The modern synthesis

It was Danish plant biologist Wilhelm Johannsen who called them genes. Genes, it was discovered, could mutate. This offered  an explanation for the emergence of new varieties – even new species – and hence for evolutionary change. In the absence of mutation, genes were immortal, immune to somatic changes, the unmoved movers that determined all bodily functions. It was not until the 1930s that the Mendelian and Darwinian mechanisms were reconciled, in the work of mathematically minded geneticists J.B.S. Haldane and Ronald Fisher in England and Sewall Wright in the US. They brought together genetics and natural selection as the accepted mechanism for evolution, called the Modern Synthesis by Haldane and Fisher and neo-Darwinism by Wright. In this synthesis, it was genes that carried the variations within a species from generation to generation. By the 1950s the formal definition of evolution had become “a change in gene frequency within a population”. Organisms had disappeared from the account; what mattered, was not even the genome but individual genes operating independently of one another – an approach derided by Sewall Wright as ‘beanbag genetics’. Unlike the mathematicians, his real-world field studies made him more aware of complexity, and of the interaction of genes during development.

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