NEW selection

Natural Selection

  • Fundamental Concept: The key to understanding natural selection lies in relative fitness.

    • Definition of Relative Fitness:

    • Contribution an individual makes to the gene pool relative to others.

    • Components of Relative Fitness:

    • Differential success in reproduction which includes:

      • Survival

      • Competition for resources

      • Resource gathering/storage

    • Additional Notes:

    • The phenotype does not have to be perfect—only better than others in a given environment.

    • The effectiveness of traits is always context-dependent on environmental factors.

Modes of Natural Selection

  • There are three primary modes of natural selection that describe how traits within a population can change.

    • Directional Selection:

    • Describes a scenario where the environment favors one end of the trait spectrum, leading to the evolution of those traits.

    • Notable Characteristics:

      • Commonly observed mode of selection.

      • The environment can fluctuate, altering the traits that are favored over time.

    • Disruptive Selection:

    • This type involves selection against intermediate phenotypes, promoting extreme phenotypes instead.

    • It can often lead to a phenomenon known as heterozygote disadvantage.

    • Potential Outcome:

      • Accelerates speciation by encouraging diversity in phenotypes.

    • Stabilizing Selection:

    • This selection opposes extreme phenotypes in favor of maintaining a stable range of phenotypes within a population.

    • The end result is often a reduction in variation within that particular trait.

Balancing Selection

  • Definition: Balancing selection refers to the processes that maintain variation within a population.

    • Key Features:

    • Density-dependent Selection:

      • A higher frequency of a certain phenotype increases competition among individuals of that phenotype.

    • Heterozygote Advantage:

      • The presence of different alleles can enhance survival and reproduction in fluctuating environments.

Sexual Selection

  • Overview: Sexual selection involves selection of traits that enhance the ability to attract mates of the opposite sex, which can lead to evolutionary changes and diversity in physical traits within species.

    • Key Concepts:

    • Sexual Dimorphism:

      • Marked difference between males and females in terms of appearance and traits.

      • These traits do not necessarily correlate with survival advantages directly.

    • Types of Sexual Selection:

      • Intersexual Selection:

      • Occurs when individuals of one sex (usually females) select mates based on traits that may signify fitness.

      • This can often take the form of displays or courtship behaviors.

      • Intrasexual Selection:

      • Involves competition between individuals of the same sex (usually males) for access to resources or mates.

      • This can lead to the development of complex mating rituals or physical contests over mates and resources.