Making a New Species
In 1937, Dobzhansky published these results in a landmark book, Genetics and the Origin of
Species. In it, he sketched out an explanation for how species actually came into existence.
Mutations crop up naturally all the time. Some mutations are harmful in certain circumstances,
but a surprising number have no effect one way or the other. These neutral changes appear in
different populations and linger, creating variability that is far greater than anyone had
This variability serves as the raw material for making new species. If the members of a population
of flies should breed among themselves more than with other members of the species, their genetic
profile would diverge. New mutations would arise in the isolated population, and natural selection
might help them to spread until all the flies carried them. But because these isolated flies were
only breeding within their own population, the mutations could not spread to the rest of the species.
The isolated population of flies would become more and more genetically distinct. Some of their new
genes would turn out to be incompatible with the genes of flies from outside their own population.
If this isolation lasted long enough, Dobzhansky argued, the flies might lose the ability to interbreed
completely. They might simply become unable to mate with the other flies successfully, or their hybrid
offspring might become sterile. If the flies were now to come out of their isolation, they could live
alongside the other insects but still continue mating only among themselves. A new species would be born.
The Modern Synthesis
Dobzhanskys ability to combine genetics and natural history attracted many other biologists to join
him in the effort to find a unified explanation of how evolution happens. Their combined work, known
as the Modern Synthesis, brought together genetics, paleontology, systematics, and many
other sciences into one powerful explanation of evolution, showing how mutations and natural selection
could produce large-scale evolutionary change. The Modern Synthesis certainly did not bring the study
of evolution to an end, but it became the foundation for future research.
An interesting note On genetic variation and ethnicity.
Read more about The Modern Synthesis.