Charles Darwin’s The Origin of Species as an audacious work that birthed a whole discipline. But it had its failings. In particular, Darwin famously lacked the Mendelian model of genetic inheritance which easily maintained variation from generation to generation. The reason that variation is important is that it is one of the major raw materials which is required from biological diversification through adaptation (natural selection and the heritability of that variation being other important components). Mendelian genetics is defined by a rearrangement of discrete units of heredity, alleles of various genes, and so solves the problem of the maintenance of genetic variation.
Genes are quite convenient as instruments of evolutionary bookkeeping, and one reason that John Maynard Smith believed that biologists had an advantage over economists in their deployment of game theory. He believed that genes were superior to various attempts by economists to measure “utility.”
Obviously, evolution is not just genes. But, if you are an evolutionary geneticist, then evolution for all practical purposes is defined by changes in frequencies of genetic variants over time.
Until very recently the genetic currency fed into the theoretical machine of evolutionary genetics was precious. There was a great deal of scarcity. A few model organisms, and a few loci. The birth of genomics meant that many common and “important” organisms were sequenced en masse. But the revolution left most of the tree of life untouched.
That is going to change very soon, as geonomicists begin to churn out sequences of a huge number of species. More importantly, they will begin to have population-scale datasets of many species.
This is a step forward from comparing single genomes of various species in a comparative sense. With population genomics researchers can inspect dynamics within numerous species across their whole genomes. This is a big deal. A lot of old questions regarding the generality and specificity, the inevitability and contingency, could be answered within a generation.