Earth Science: Evolution – Evolutionary Factors
Following the synthetic theory of evolution, the development of life proceeds nondirectionally through the random effect of evolutionary factors. Selection and genetic drift are the most important evolutionary factors.
Earth Science: Biology – Evolution – Selection
Organisms that are particularly well adapted to their environment generally have better chances of survival and reproduction, therefore prevailing over other individuals. This development is referred to as natural selection.
Among the large number of members of a population, those with the greatest likelihood of reproducing are the ones that are-based on their characteristics-best adapted to the so-called selection factors prevailing in a particular habitat. These factors can be either of an abiotic nature- relating to humidity or temperature—or of biotic nature—pertaining to other living beings, such as predators and parasites.
The ability of an individual’s genes to contribute to the gene pool of the next generation is referred to as fitness, while the influence of selection factors onto a population is known as selection pressure. Stabilizing selection occurs when a population is so well adapted to its environment, that deviant mutants are constantly being eliminated due to selective pressures acting on the phenotype.
Due to changing environmental conditions, one-sided selection pressure may favor individuals with certain alleles, so that their proportion increases within the population. This process is called transforming selection. In the event of splitting selection, those individuals that occur most frequently are being pushed back the strongest. Therefore individuals with specific, marginal characteristics have an advantage and are better able to assert themselves, which can ultimately even lead to a population split into two species.
For instance, infectious diseases can be such a selection factor.
Genetic drift
The term “genetic drift” refers to a random change in the genetic diversity of a population. This can occur, for instance, when only a few individuals from a large population migrate into a new area. Such “founder individuals” represent a random selection of genotypes. Therefore, a random change of the gene pool becomes more likely the smaller a population is.
A genetic drift can also happen when part of a population is suddenly destroyed. For instance, if both the environmentally well-adapted and less well-adapted members of a population die in a natural catastrophe, a coincidental section of individuals survives and the gene pool of the population subsequently shifts at random.
DOMESTIC ANIMALS
The many races of domestic animals can serve as an example of transforming selection.
This race diversity is the result of unnatural breeding conditions which tend to create genetic changes particularly fast, because only specific variants are selected that suit a particular breeding objective.
Due to these selective mechanisms, a common base form, such as the wolf, has given rise to many dog races in a comparatively short period of time.