Born in Africa_ The Quest for the Origins of Human Life - Martin Meredith [26]
But different schools of evolutionists—experimental geneticists, naturalists, palaeontologists and developmental biologists—tended to regard each other with mutual incomprehension and pursued their own research separately. As the American palaeontologist George Gaylard Simpson noted in 1944:
Not long ago, paleontologists felt that a geneticist was a person who shut himself in a room, pulled down the shades, watched small flies disporting themselves in milk bottles, and thought that he was studying nature. A pursuit so removed from the realities of life, they said, had no significance for the true biologist. On the other hand, the geneticists said that paleontology had no further contributions to make to biology, that its only point had been the completed demonstration of the truth of evolution, and that it was a subject too purely descriptive to merit the name ‘science.’ The palaeontologist, they believed, is like a man who undertakes to study the principles of the internal combustion engine by standing on a street corner and watching the motor cars whiz by.
The breakthrough began in the 1930s. Geneticists found that mutations alone did not provide an adequate answer to the conundrum of evolution; natural selection, too, played a role in changing the frequencies of genes in populations. Population genetics and fruit fly experiments showed that most variation was due to a recombination of genes from both parents but that additional variation was the result of slight mutations. These random variants were then weeded out by natural selection. Selection by the environment affected the degree to which a particular gene could spread within a population; the stronger the selection, the more rapid the genetic change.
The outcome that emerged during the 1940s was a synthesis that combined Darwin’s mechanism of natural selection with the developing understanding of the mechanism of heredity. It was known as the ‘Neo-Darwinian synthesis’, or ‘modern synthesis’; and it put an end to the perennial feuds of rival schools of evolutionists. Evolution, it was agreed, was a gradual, long-term process consisting, essentially, of the accumulation within lineages of small genetic mutations and recombinations which, over long periods of time, resulted in large effects. This generation-to-generation modification of gene frequencies was guided by the hand of natural selection. These processes explained not only changes within species but also the origins of new species and biotic diversity.
Advances in genetic research added weight to the synthesis. In 1944, Oswald Avery and two colleagues established that genetic information is contained not in cell proteins, as had been thought previously, but in nucleic acids—in DNA (deoxyribose nucleic acid) molecules. Their discovery marked the start of the ‘molecular revolution’. A further crucial breakthrough came in 1953, when James Watson and Francis Crick deciphered the double-helix structure of the DNA molecule in which genetic information is coded.
Other ideas incorporated into the synthesis, however, proved to be more controversial. Two of its principal architects, the geneticist Theodosius Dobzhansky and the ornithologist Ernst Mayr, considered the evolutionary history of humans to have been different from that of other organisms, proceeding upward in a straight line rather than by trial and error. Dobzhansky’s argument was based on the advent of human culture, in particular toolmaking. Culture, he said, had removed humans from the effects of the natural environment and therefore from natural selection, enabling them to adapt to a diversity of environments. The process of acquiring culture, he argued, must have been confined to a single hominid species. He explained the differences that existed among living and extinct humans as being