Processes That Lead to Evolution

Four processes lead to evolution: mutation, natural selection, migration, and genetic drift.

Mutation: A change in the DNA of an organism, i.e., a change in the inherited characteristics. A mutation in reproductive cells may be passed on to the next generation, where it may result in birth defects or genetic disease. (DNA: A gene—a distinct piece of DNA that determines the characteristics an individual displays). When DNA is changed the DNA is said to have undergone mutation.

In extreme cases, cells or offspring with mutation cannot survive. In less extreme cases, individuals with mutation are so different from their parents that they cannot reproduce with the normal offspring. In milder cases, the mutation can simply add variability of the inherited characteristics. So the change is not always for better: Mutation can result in a new species whether or not that species is better adapted than its parental species to the environment.

Natural Selection

Natural selection is the process that determines which individuals within a species will reproduce more effectively and therefore results in changes in the characteristics within a species.

                                              

Migration

The migration of one population of a species into a habitat previously occupied by another population can lead to changes in gene frequency. Sometimes reproductive structures like seeds of flowering plants are blown by the wind and moved by animals.

Genetic Drift

It refers to changes in the frequency of a gene in a population as a result of chance rather than the other three processes of evolution. Chance may determine which individuals become isolated in a small group from a larger population and thus which genetic characteristics are most common in that isolated population. Genetic drift can occur in any small population. It can be a problem for a rare or endangered species: (1) characteristics that are less adapted to existing environmental conditions may dominate, making the chance of survival of the species less likely; (2) genetic variability of the species is greatly reduced, meaning that its ability to adapt to future changes in the environment through natural selection has been reduced.  

Terms related to Species Habitat

Exotic species: A species introduced into a new geographic area. (Invasive species, a foreign species, not native, usually cause economic or environmental damage).

Endemic species: A species that is native to a particular area and not native elsewhere. For example, Monterey pine is endemic to a portion of the California coast and exotic in New Zealand.

Cosmopolitan species: A species with a broad distribution, occurring all over the world wherever the environment is appropriate. (house mouse).

Ubiquitous species: A species that are found almost anywhere.  (humans, E. coli).

Habitat:  Place or type of place where an organism or population of organisms lives.