The History of Evolutionary Theory, and the Implications of Genetics
Had Charles Darwin, the man who coined the mechanism of evolution as "natural selection" been introduced to Gregor Mendel, the geneticist who first described gene inheritance, biologists today would be decades ahead of where we are in terms of research. For it is genetics, the phenomenon of traits being inherited by offspring from their parents, that provides the vessel for all evolutionary change. Charles Darwin and the biologists of his day imagined that there was a mechanism for inheritance. They thought there was a means through which the characteristics of parents can be passed on to their offspring, but they couldn't fully describe it. Darwin, in his famous On the Origin of Species, implicated genetics as the vehicle for natural selection, and thus evolution, without even knowing the word.
...owing to this struggle, variations, however slight and from whatever cause proceeding, if they be in any degree profitable to the individuals of a species in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals and will generally be inherited by the offspring. The offspring also will thus have a better chance of surviving, for of the many individuals of any species which are periodically born, but a small number can survive I have called this principle by which each slight variation, if useful, is preserved, by the term Natural Selection in order to mark its relation to natures's power of selection...
In the decades after Darwin's death, his theory of evolution began to fall by the wayside in scientific literature. By the 1920's and 30's, many scientists thought that it was at best an interesting hypothesis, but without merit, as the mechanism for natural selection had yet to be identified and no observation had been made of a single speciation event. Darwin spoke of natural selection as the driving force behind the emergence of new species. In-fact, this was the very thesis of his book. But no one had yet been able to describe the phenomenon. The study of genetics continued to develop separately from evolutionary theory, only occasionally being referenced by biologists interested in heredity. It wasn't until the 1940's, with the publication of British Biologist Julian Huxley's Evolution: The Modern Synthesis, that a solid connection was made between genetics and evolutionary theory. Huxley and many other biologists were the proponents of a rebirth of Darwin's ideas; an intellectual movement known as "neodarwinism." It is through their synthesis of genetics and evolutionary theory that a clearer picture of the evolution we know today emerged.
From Mutations to Modern Synthesis Theory -- How We See Genetics and Evolution Today
The ideas surrounding Populuation Genetics presented in Chapter 6 were the bridge needed between genetics and natural selection that led to what we know as evolution today.