Evolution refers to processes that change the genetic make up of a population over time.
Evolution is the basis for diversity of life.
Evolution occurs when there are changes in the allele frequencies within a population across generations.
Natural selection, genetic drift, gene flow, and mutation are the main mechanisms that drive evolution
Although each process has a distinct impact on populations, they frequently cooperate to influence evolutionary outcomes.
1. Mutation
Mutation refers to change in the DNA sequence of an organism. Mutation is the main cause of genetic variation and introduces new alleles into a population. Errors in DNA replication, exposure to environmental factors (like radiation or chemicals) etc., lead to mutation. Mutations sometimes can occur spontaneously also.
Mutations can have different effects:
- Beneficial mutations : These are advantageous to individuals favouring their survival and propagation
- Neutral mutations : These mutations do not affect the individual but add variation to the gene pool.
- Harmful mutations : These mutations may reduce an individual’s chances of survival or reproductive success.
Irrespective of the types ,mutations can be favored by natural selection, contributing to adaptation and evolutionary change.
2. Gene Flow
Gene flow (or migration) refers to the transfer of alleles from one population to another . This is achieved through the movement of individuals or their gametes (e.g., pollen in plants). Gene flow introduces new alleles into populations, increasing genetic variation and potentially changing allele frequencies.For instance, new genetic material is introduced into a population when individuals with distinct alleles from one population relocate to another. This introduces beneficial alleles in a population that can be acted upon by natural selection.
Examples of Gene Flow in Evolution
Human Populations: Intermarriage and migration in contemporary human populations result in gene flow, which reduces regional distinctions and creates shared genetic features across continents.
Island Species: Occasional gene flow from mainland populations can preserve genetic diversity and introduce advantageous alleles into island populations where isolation can cause fast genetic drift.
Hybrid Zones: Gene flow can obfuscate species boundaries in areas where two species or different populations converge and breed. It’s possible for hybrid offspring to acquire a mix of features from both populations, which could result in novel adaptive combinations.
3. Genetic Drift
Genetic drift refers to random changes in allele frequencies within a population. It results from random chance, particularly in small populations.
Unlike natural selection, genetic drift does not favor beneficial alleles
There are two key types of genetic drift:
- Bottleneck Effect: This refers to dramatic reduction in size in population due to events like natural disasters. In such a case only a small subset of the population’s alleles may survive, reducing genetic diversity.
- Founder Effect:When a small group breaks away from a larger population to establish a new population, it may carry only a fraction of the genetic diversity of the original population.
Genetic drift can lead to significant evolutionary changes over time, especially in small populations where random events have a larger impact.
4. Natural Selection
Natural selection is the process by which nature selects individuals with certain heritable traits that are more likely to survive and reproduce than others due to those traits. With time , natural selection increase the frequency of beneficial alleles and decrease the frequency of harmful ones.It leads to adaptation and organisms become better suited to the environment.
There are several types of natural selection:
- Directional Selection:This type of natural selection favors one extreme phenotype over others. This causes a shift in allele frequencies in that direction.
- Stabilizing selection reduces diversity and preserves the status quo by favoring the average phenotype.
- Disruptive selection may result in the emergence of new species by favoring extreme phenotypes at both extremes of the spectrum.
5. Sexual Selection
A type of natural selection known as sexual selection occurs when traits icrease an individual’s chances of attracting mates and reproduction. It may result in pronounced behavioral or physical variations between a males and females (sexual dimorphism).
Competition for mates within one sex (often males) is known as intrasexual selection.
Intersexual selection is the process by which members of one sex—typically females—select partners based on specific desirable characteristics.
Sexual selection can lead to the evolution of traits that may not necessarily enhance survival but do improve mating success, such as bright plumage in birds .
6. Non-Random Mating
Non-random mating occurs when individuals in a population choose mates based on specific traits, which can affect allele frequencies over time. This mechanism doesn’t directly cause evolution but can influence how other evolutionary processes work.
- Assortative Mating: Individuals prefer mates with similar phenotypes (e.g., size, color), which can increase the proportion of homozygous individuals.
- Disassortative Mating: Individuals prefer mates with different phenotypes, which increases heterozygosity and genetic diversity.
Interplay of Mechanisms in Evolution
In natural populations, these mechanisms often interact in complex ways. For instance:
- Gene flow can restore lost alleles in isolated populations, thereby counteracting genetic drift.
- The genetic variety brought about by mutation and gene flow may be subject to natural selection.
- The features that become more prevalent in subsequent generations can be influenced by sexual selection and non-random mating.
Together, these evolutionary processes drive adaptation, speciation, and long-term population shifts, so influencing the diversity of life on Earth.
- Watch the video of Five fingers of evolution by Paul Andersen from TED-Ed to understand the mechanism of evolution
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