Science Quote by Ernst Mayr

Ernst Mayr is pushing back against a reduction he saw in early population genetics. Fisher, Haldane, and Wright gave biologists a precise language of allele frequencies, selection coefficients, and drift, and it was intoxicating to say that evolution is just genes shifting in a population. Mayr argues that this neat formula erases a crucial duality. Evolution advances along two axes at once: adaptation, the fine-tuning of organisms to their environments, and diversification, the branching of lineages into new species. They are related but not the same, and they require different kinds of explanations and evidence.

Adaptation can often be described by changes in gene frequencies. Selection and drift within a single interbreeding population can be modeled, measured, and even reproduced in the lab. Diversification is different. It depends on the splitting of gene pools, the origin of reproductive isolation, and the geography of separation. Speciation is a historical, spatial, and ecological process: islands, mountain ranges, host shifts, sexual signals, and isolating mechanisms all matter. A definition of evolution that stays inside one panmictic population misses the moments when the population ceases to be one.

Mayr’s lifelong work in systematics and biogeography sharpened this perspective. He championed the biological species concept and allopatric speciation, pointing out that the world’s biodiversity is a record of repeated splits, not just continuous transformation. Darwin himself paired natural selection with common descent and the branching tree of life; Mayr is reminding geneticists to honor both halves. Adaptation tends to be gradual and ongoing; diversification is often episodic, tied to ecological opportunity or isolation, and leaves signatures in phylogenies and fossil records.

The legacy of this critique is a more integrative evolutionary biology. Population genetics remains essential, but it is complemented by speciation theory, phylogenetics, ecology, and paleontology. Together they capture both the honing of fit and the proliferation of forms that make up evolution.