Evolution: Change in heritable traits of a population over generations.
Natural Selection: A primary mechanism of evolution where the fittest traits are selected for reproduction based on environmental fitness.
Genetic Drift: A mechanism of evolution involving random changes in the frequency of traits in a population, not necessarily related to traits' environmental fitness.
Natural Selection
Involves variation in heritable traits within a population.
Traits that provide a reproductive advantage are more likely to increase in frequency.
Example: In a population of living circles, blue circles may reproduce more due to advantages like avoiding predators.
Genetic Drift
Involves random changes in the frequency of traits in a population.
Does not select for traits based on environmental fitness.
More significant in small populations.
Example of Genetic Drift
Rabbit Population:
Population of 10 rabbits with a gene for color.
Two alleles: Capital B (dominant, brown) and lowercase b (recessive, white).
Equal number of each allele at the start.
Random reproductive success changes allele frequency over generations.
Randomly, the top 5 rabbits reproduce, increasing the frequency of capital B alleles.
Further random events could lead to the disappearance of the white allele.
Types of Genetic Drift
Bottleneck Effect
Caused by a major disaster or event reducing population size drastically.
Surviving individuals may not be the fittest but are those not affected by the disaster.
Results in reduced variation and potential loss of alleles.
Founder Effect
Occurs when a small group separates from a larger population to establish a new one.
The founders have less genetic variation, leading to initial genetic drift.
Example: A few organisms discovering a new area can lead to a new population with reduced variation.
Implications of Genetic Drift
Small Populations: More susceptible to significant changes in allele frequencies due to random events.
Diversity Loss: Critical concern for biologists, especially in small populations, as genetic drift can reduce genetic diversity.
Random Selection: Unlike natural selection, genetic drift does not favor advantageous traits, which can lead to the loss of beneficial traits.
Conclusion
Both natural selection and genetic drift are mechanisms of evolution but operate differently.
Natural selection focuses on environmental fitness, while genetic drift is about random changes not linked to fitness.
Understanding both processes is crucial for studying evolutionary biology.