Mechanism of Evolution – Class 12 | Chapter – 7 | Biology Short Notes Series PDF
Mechanism of Evolution: Evolution is simply change over time. Darwin proposed that the mechanism of evolution by which this change occurs was natural selection, which is considered by most scientists as the main mechanism for evolution. There are, however, several other mechanisms or processes which affect evolutionary change. Man is directly affecting the evolution of organisms through artificial selection and recombinant DNA technology.
There are also non-selective mechanisms which result in changes in a gene pool of populations, including gene flow (or migration), genetic drift and the founder effect. Endosymbiosis is the accepted theory as to the mechanism of how eukaryote cells arose from the symbiotic relationship between bacterial cells. It is also an interesting, but controversial, explanation for driving evolutionary change.
Mechanism of Evolution
- Mutation: It is a driving force of evolution, is a random change in an organism’s genetic makeup, which influences the population’s gene pool. It is a change in the nature of the DNA in one or more chromosomes. Mutations give rise to new alleles; therefore, they are a source of genetic variation in a population.
- Gene Flow: It occur during the migration of individuals from one group or location to another. When the migrating individuals interbreed with the new population, they contribute their genes to the gene pool of the local population. This establishes gene flow in the population.
- Genetic Drift: It occurs when a small group of individuals leaves a population and establishes a new one in a geographically isolated region. For example, when a small population of fish is placed in a lake, the fish population will evolve into one that is different from the original. Fitness of a population is not considered in genetic drift, nor does genetic drift occur in a very large population.
- Natural Selection: It occurs when populations of organisms are subjected to the environment. The fittest creatures are more likely to survive and pass their genes to their offspring, producing a population that is better adapted to the environment. The genes of less-fit individuals are less likely to be passed on to the next generation. The important selective force in natural selection is the environment.
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