Principles of Natural Selection

Table 16.1 Principles of Natural Selection Observations About Populations l Natural populations have an inherent reproductive capacity to increase in size over time. I As a population expands, resources that are used by its individuals (such as food and living space) eventually become limited. I When resources are limited, the individuals of a population compete for them. Observations About Genetics l Individuals of a species share certain traits. l Individuals of a natural population vary in the details of those shared traits. l Shared traits have a heritable basis, in genes. Alleles (slightly different forms of a gene) arise by mutation. Inferences l A certain form of a shared trait may make its bearer better able to survive. I The individuals of a population that are better able to survive tend to leave more offspring. l Thus, an allele associated with an adaptive trait tends to become more common in a population over time.