Microevolution

Definition: Mutation refers to a permanent alteration in the DNA sequence that makes up a gene. This change can occur in different forms such as insertion, deletion, or substitution of nucleotides.
Example: A mutation in a gene that changes the color of flowers from red to white due to a change in pigment production.

Definition: Natural selection is the process by which organisms better adapted to their environment tend to survive and produce more offspring. This leads to gradual changes in the traits of organisms over generations.
Example: In a population of moths, those with coloration that provides better camouflage against predators are more likely to survive and reproduce, leading to a predominance of that coloration in future generations.

Definition: Sexual selection is a form of natural selection where individuals with certain inherited traits are more likely than others to obtain mates. This can lead to the evolution of traits that enhance mating success but may not necessarily improve survival.
Example: The bright plumage of male peacocks attracts females, demonstrating how traits that enhance reproductive success can evolve, even if they make the males more visible to predators.

Definition: Genetic drift is a mechanism of evolution that involves random changes in allele frequencies within a population, especially in small populations. It can lead to the loss of genetic diversity.
Example: A bottleneck event occurs when a large population is drastically reduced in size due to an environmental event. The surviving population may have a different allele frequency than the original population, leading to genetic drift. - Bottleneck Event: For example, a natural disaster that kills off a large portion of a population leaves only a subset of individuals resulting in a loss of genetic diversity and altered allele frequencies.

Definition: Gene flow (or gene migration) is the transfer of genetic material between populations through migration of individuals or gametes (e.g., pollen). It increases genetic diversity and can also introduce new alleles to a population.
Example: If individuals from Population A migrate to Population B, the introduction of new alleles can change the allele frequencies in Population B and enhance genetic variation.

The interplay of mechanisms such as mutation, natural selection, and genetic drift can lead to speciation—the formation of new species.

Reproductive Barriers: As species evolve, reproductive barriers can develop that prevent different species from interbreeding. This is critical for speciation. - Dobzhansky's Principle (1937): Explains that speciation involves the evolution of reproductive barriers in populations that can otherwise interbreed.
Meta-Populations: A group of populations that exchange individuals through dispersal. Each small population may evolve independently if isolated due to reproductive barriers, making distinct forms easier to maintain. - Example: A species divided across different islands may evolve separately due to isolation but may still share genes through migration among islands.
Isolation: If a population is cut off from others due to geographical barriers or other factors, it may diverge significantly, leading to the emergence of new species.
Archipelagos: Groups of islands that serve as a model system for studying speciation. Populations on isolated islands may evolve distinct traits while remaining linked through dispersal.
Common Ancestry: Speciation can be traced back to common ancestors where groups of organisms such as finches on the Galapagos Islands diversified into distinct species adapted to different environments.

Hybrid Zones: Regions where two distinct populations interbreed, leading to varying outcomes: 1. Reinforcement: Strengthening of reproductive barriers. 2. Fusion: Merging of two species back into one. 3. Stability: Continued presence of hybrids without significant changes in species status.

Sympatric Speciation: Occurs when groups within a species evolve to become different species without physical barriers. An example is the formation of host races in species like Rhagoletis pomonella, where different groups specialize on different host plants, leading to reproductive isolation and eventually speciation.