Through the first half of the twentieth century there was one big idea about evolution, marked by four scientists who published separately in the 1930s and three others whose works came out in the early 1940s.

The first was Dobzhansky’s 1937 Genetics and the Origin of Species. It went on from the work of Fisher, Haldane and Sewall Wright with the view that  real world populations had far more genetic variability than the early population geneticists had thought. Not only did natural selection help to retain this diversity but it also drove change and managed mutation.

Then two other zoologists looked outwards at the environmental conditions of these populations. EB Ford studied butterflies to show that geographical separation helped strengthen the genetic identity of whole populations, while Ernst Mayr’s 1942 Systematics and the Origin of Species elaborated on the effects of this isolation and went on to define a species: as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.

He also showed how they adapted to slight differences in the environment and described slightly different reactions to slightly different geographical variations.

Aware that the disparate biological sciences needed bringing together, the leading New York biologists tried to encourage debate between their supporters through an organisation ambitiously entitled Committee on Common Problems in Genetics and Palaeontology. But it was war-time in the United States as well as in Europe so travel was difficult; many of the major players on the evolutionary stage were away on military service and those left behind weren’t able to do very much. It was left to Julian Huxley in London to join together all those ideas from different specialisms. He did it in style and provided those left working in biology with plenty of ideas to take forward in a more integrated style of cooperation.

Undaunted, Huxley published his major work about their big idea: Evolution: the Modern Synthesis later in 1942 and announced it as “this reborn Darwinism, this mutated phoenix risen from the ashes of the pyre kindled by men so unlike as Bateson and Bergson”. It put to rest the idea that Mendel’s theory only recognised large mutations, and explained instead that it applied just as well to continuous small-scale genetic changes. Furthermore, these different sized genetic differences occurred universally in all organisms in the same way. The changes could have happened across whole populations of the same species, and so accounted for the mathematical demonstrations of natural selection that Fisher and Haldane had recently made.

Who was to say that any of these explanations were unworthy? Although eventually they all turned out to be wrong, they were all of their time, popular trends within their society, often reflecting or giving it a structure and a sense of purpose. As society changed so these explanations ceased to hold on to their acceptable role, failing to link to new situations and causes. They didn’t stand up to continuing verification, even proving to be false in some scenarios. Huxley’s Modern Synthesis set out timely alternatives to these rejected theories, sorted through the mass of disciplines that had originated and developed since the First World War, rejected the stale failures and encouraged the promising new world. There was genetics, statistics, biochemistry, systematic, universal modules, environment, isolation and time, all within adaptation and selection.

One of the most important themes that came up again and again in Huxley’s Synthesis was “Progress without a goal”. It was the first time that evolution had been explicitly discussed in this way, so different to the old and difficult concepts “primitive” and “advanced” and the prejudiced evolutionary sequences and styles of adaptation to subtle environmental changes. In turn, it also invalidated much of what had been thought and said about “degeneration” since Lankester’s day, though there was still a connection between that idea of limited human development and the eugenicists’ aims to control the growth of human population.

Importantly, as biology began to pick itself up after the war, and after the revelations of the attempts by Hitler and Stalin to practice different eugenic strategies, some of the ways of thinking about human population biology and human race quickly changed from what had been set down in the Modern Synthesis. Most scientists felt they had learnt a hard lesson about the difficulties of linking their work to politics. In 1950 Huxley influenced the wording of a UNESCO statement that: “A race, from a biological standpoint, is one of the group of populations constituting the species Homo sapiens.” The three major divisions are Mongoloid, Negroid and Caucasoid, and “Catholics, Protestants, Moslems and Jews are not races.”

War forced the re-evaluation of what life meant to most of the people involved: both the hard physics and chemistry of it, the softer psychological impact and its philosophical explanation.