Adaptation by natural selection acting over generations is one important process by which species change over time in response to changes in environmental conditions. The traits of organisms that survive a change in the environment are inherited by offspring and become more common in the population. The traits of organisms that cannot survive a change in the environment are not passed to offspring and become less common. In separated populations, the changes can be large enough that the populations evolve to become separate species. Extinction occurs when the environment changes and the adaptive characteristics of a species, including its behaviors, are insufficient to allow its survival.
Adaptation and Diversity