Here is the irony of the "PDF" search. Population genetics is the study of discrete particles (genes) in finite populations (people, flies, trees). But Crow and Kimura ask you to think of evolution as a continuous, flowing river.
They use calculus to describe the stochastic (random) fate of a single mutation. They treat a population of millions as a single "effective size" (Ne). They force you to accept a terrifying truth: Most of evolution is not dramatic survival of the fittest. Most of evolution is the random drift of neutral mutations. an introduction to population genetics theory pdf
"The average heterozygosity of a population is simply 4Nu/(1+4Nu)." — A line from the book that, once understood, changes how you see your own genome. Here is the irony of the "PDF" search
Crow and Kimura rescue the abstract concept of F-statistics from pure math and make it biological. "F" measures the probability that two alleles are identical by descent. It is the currency of relatedness. When you read their derivation, you realize that every mating is, to some tiny degree, incestuous—and that this dictates the entire genetic load of a species. "The average heterozygosity of a population is simply
Kimura was a wizard of applied mathematics. He realized that watching a gene jump from 10% frequency to 11% is impossible to track. So, he treated probability as a fluid. The "Kolmogorov forward equation" becomes a map of genetic destiny. You learn that a new mutation has a probability of fixation equal to its initial frequency—usually 1/(2N). In a population of 10,000, a single new mutant has a 0.005% chance of taking over. The rest? Lost to the void.