How exactly can natural selection work?
Natural selection requires four conditions in order to operate: • Reproduction: Organisms must reproduce themselves, creating a new generation of individuals. • Heredity: The characteristics of the parents must tend to be present in the offspring. • Variation: Different individuals in the population must be different in at least some characteristics from each other. • Differential fitness: Some individuals must be more fit (that is, more likely to survive long enough to reproduce) than others, based on their varying characteristics. (Ridley 1993) By definition, living things must reproduce themselves. Thus condition #1 is fulfilled. As Mendel first proved in the 19th century, parental characteristics are passed to the offspring. While the lack of a known mechanism for heredity was a primary weakness of Darwin’s theory when it was first proposed (Ridley 1993), today the mechanisms of gene transfer and expression are well understood. Thus condition #2 is fulfilled. Darwin recognized that
