Haldane, Mayr, and Beanbag Genetics

Haldane, Mayr, and Beanbag Genetics

Haldane, Mayr, and Beanbag Genetics

Haldane, Mayr, and Beanbag Genetics


Haldane, Mayr, and Beanbag Genetics presents a summary of the classic exchange between two great biologists - J.B.S. Haldane and Ernst Mayr - regarding the value of the contributions of the mathematical school represented by J.B.S. Haldane, R.A. Fisher and S. Wright to the theory of evolution. Their pioneering contributions from 1918 to the 1960s dominated and shaped the field of population genetics, unique in the annals of science. In 1959, Mayr questioned what he regarded as the beanbag genetic approach of these pioneers to evolutionary theory, "an input or output of genes, as the adding of certain beans to a beanbag and the withdrawing of others." In 1964, Mayr's contention was refuted by Haldane in a remarkably witty, vigorous and pungent essay, "A defense of beanbag genetics" which compared the mathematical theory to a scaffolding within which a reasonably secure theory expressible in words may be built up. Correspondence between Haldane and Mayr is included. Beanbag genetics has come a long way since 1964. Mayr's (1959) critique of simple uncomplicated population genetics is no longer valid. Population genetics today includes much more than Mayr's beanbag genetics. Population genetics models now include multiple factors, linkage, dominance and epistasis. These may be regarded as the advanced beanbag models. Furthermore, population genetics and developmental genetics have become interdependent. Contemporary beanbag genetics includes molecular clocks, nucleotide diversity, coalescence and DNA-based phylogenetic trees, along with the four major holdovers from classical genetics, mutation, selection, migration and random drift. Molecular genetics has made it possible to study evolution rates at the nucleotide level. It is also possible today to compare DNA similarities and divergence in diverse species of animals and plants, which were not previously crossable.


A fact in science, is not a mere fact, but an instance.

— Bertrand Russell

This book is about the views of two famous biologists, both now deceased, and how they differed on a central issue in evolutionary biology. As their correspondence indicates, theirs was a friendly disagreement—there was no animosity or bitterness in their arguments. Indeed, as Ernst Mayr once wrote in a letter to J.B.S. Haldane, it is all a matter of emphasis and interpretation. Their differences reflected their backgrounds and experience.

The term “beanbag genetics” is derived from the fact that the early Mendelians used to keep different colored beans in bags for the purpose of counting and analyzing Mendelian ratios. This method implied that genes behaved as isolated independent entities with no interaction with each other. Mayr (1959, 1963) used the term “beanbag genetics” to describe the methodology and the underlying concepts of early studies in theoretical population genetics by R.A. Fisher (1930), Haldane (1932a), and Sewall Wright (1931). This was especially true of Fisher and Haldane, who used simple models of genes acting in isolation for the sake of mathematical convenience. in his opening address to the 1959 Cold Spring Harbor Symposium on Qualitative Biology “Genetics and Twentieth-Century Darwinism,” Mayr challenged the great pioneers of population genetics: “But what, precisely, has been the contribution of this mathematical school to the evolutionary theory, if I may be permitted to ask such a provocative . . .

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