Before the molecular revolution, the major techniques in animal behavioral genetics included selection experiments, crosses between inbred lines, and quantitative genetic analyses.
However, great difficulty in figuring out the causal mechanisms underlying genetic gain for complex traits limits our understanding of the genetics underlying selection response.
In ecological evolutionary genetics, hard selection is considered global density regulation in contrast with the local density regulation of soft selection (Whitlock 2002; van Dyken 2010 in press).
Multiple lines of evidence for evolution are presented (fossils, homologous structures, genetics, artificial selection, etc).
The corresponding assigned chapters were titled "Random events in population genetics," "Natural selection and random drift," and "Adaptive explanation" (Ridley 2004).
The understanding that the evidence for evolution comes from multiple sources and sciences, including but not limited to paleontology, geology, genetics, artificial selection, and comparative anatomy.
Today, with the insight provided by Mendelian and molecular genetics, natural selection is recognized as a primary component of evolutionary change, especially adaptation.
Note, however, that on the "received view" (Sarkar 2004, 2005b) of evolution based on population genetics, natural selection does not act between species.
They have no understanding of genetics or selection and hold no long-term goal to become domesticated they simply happen to possess traits of interest or they do not.
This causal dimension to evolutionary explanations is echoed in population genetics, where selection, mutation, migration and random drift are often described as causes, or 'forces', which lead to gene frequency change (Sober 1984).
