Natural Selection & Artificial Selection

Mechanism of Evolution: Developed by Charles Darwin, natural selection is the process where individuals with advantageous phenotypes survive and reproduce at higher rates.
Sequence of Events: * Phenotypic variation exists in a population. * Competition for limited resources occurs. * Favorable phenotypes lead to higher reproductive fitness. * Alleles for beneficial traits increase in frequency over generations.
Environmental Factors: Both biotic (e.g., predators) and abiotic (e.g., temperature, water availability) factors influence evolutionary direction.
Importance of Variation: Genetic differences, such as mutations, provide the raw material for adaptation; higher variation enhances a population's ability to survive environmental changes.
Scale of Evolution: Natural selection acts on individuals, but evolution is measured in populations over time.

DDT Resistance: In insect populations, the application of DDT (Dichlorodiphenyltrichloroethane) acts as a selective pressure; individuals with resistance mutations survive and reproduce, shifting the population to be predominantly resistant.
Sickle Cell Anemia: In malaria-prevalent regions, carrying one sickle cell allele (heterozygotes) increases fitness by providing resistance to malaria.
Climate Change and Fitness: Shifting flowering times due to global warming can cause a mismatch with pollinators, resulting in reduced seed production and lower evolutionary fitness.

Process: Humans conduct selective breeding by choosing individuals with desirable traits to reproduce over many generations.
Objectives: Enhance specific traits or combine multiple features, such as high yield and disease resistance in crops.
Common Examples: * Increased milk yield in cattle. * Faster racehorses. * Disease-resistant crops.

Definition: Unrelated species evolve similar phenotypic characteristics independently due to similar environmental selection pressures.
Biological Example: Dolphins (mammals) and sharks (fish) have both evolved streamlined body shapes for aquatic environments.
Human-Induced Convergence: Artificial selection applied to different species for similar goals can lead to convergent traits: * Maize (corn) and sorghum bred for high yield and drought resistance. * Tomatoes and peppers bred for fruit size and color. * Cows, sheep, and goats bred for increased milk production, resulting in similar physiological traits like larger udders.