Natural selection results in the following phenomena at both the molecular level and the population level:
Diversity
Diversity can refer to either the number of different characteristics present in a population or the number of different species in an area. On the environmental level, diversity creates stability in ecosystems and biomes. This is called biodiversity. A community that has biodiversity will not be seriously affected by the extinction of one or two species. On the species level, diversity allows the species to survive in a changing environment.
Humans affect the diversity of a species through the following two processes:
· Selective breeding—the breeding of organisms that have a certain desired trait
· Genetic engineering—the manipulation of genes that allows scientists to put genes from one organism into another organism
Adaptation
An adaptation is a structure or behavior that helps an organism survive in its environment long enough to reproduce.
Structural adaptations can include traits that improve the ability to find food, protection, or move from place to place. Most adaptations take long periods of time to develop fully. However, some species are capable of fairly significant change over only a few generations.
Many forms of behavior, including the evasion of predators, the ability to cooperate with other individuals of the same species, and the desire to mate, are governed by traits. Organisms with traits that produce beneficial behaviors are more likely to survive long enough to reproduce. Therefore these traits are more likely to be passed down through the generations and spread throughout a population.
Speciation
Speciation is the process by which two populations of the same species become so different that they can no longer interbreed. Speciation can occur in a few ways, but the end result always increases biodiversity. The following process describes the general steps that occur in most cases of speciation.
1. Separation
Different populations of the same species become isolated from one another.
2. Adaptation
The separated populations develop different responses, or adaptations, to the different selective pressures found in the newly isolated environments.
3. Division
Over a long period of time, the divided populations develop enough changes to their genetic material that they are no longer able to breed with one another.
Speciation can also occur due to a mistake during meiosis, in which too the chromosomes do not separate correctly. The result is an offspring with an extra set or sets of chromosomes, known as polyploidy. This is common in plants. In this case reproductive isolation is immediate, even if the individual is not separated from the rest of the population.
Extinction
Extinction refers to the process of a species dying out completely. The extinction of a species occurs when environmental changes and adaptive characteristics are insufficient to permit survival.
Phylogeny
A phylogeny illustrates the evolutionary history and development of a species. While natural selection works on the individual level, it eventually affects the species as a whole. Therefore natural selection is one of the main instruments of phylogeny.