Evolution is tree-like as lineages split and extinction occurs. Current theory adheres to much of Darwin's thinking. Nature of the species. Evidence for Evolution by Natural Selection Increaseed evidence for variability within species, and response to selection. Size of male house sparrows in North America.
Size is measured as a principal component of score, derived from skeletal measurements.
Selection for better and worse teeth in rats. The age in days at which the rats in the 2 lines developed caries was measured.