Darwin's Theory of Natural Selection

Darwin's Theory of Natural Selection

• Lamarck proposed evolution through use and disuse of traits within an organism's lifetime, with these acquired traits passed to offspring.
• Darwin's theory of evolution centers on natural selection, where advantageous traits increase survival and reproduction.
• Variation refers to differences in physical traits among individuals within a species.
• Adaptation is a heritable trait enhancing an organism's survival and reproduction in its environment.
• Artificial selection involves humans breeding organisms for desired traits, such as in dog breeding.
• Natural selection is the process where advantageous traits enable organisms to survive and reproduce more successfully.

Four Principles of Natural Selection

• Variation exists within populations
• Traits are heritable
• Overproduction leads to competition for survival
• Advantageous traits enhance survival and reproduction

Examples in Action

• Galapagos finches with larger beaks survived a drought due to their ability to eat tougher seeds.
• Peppered moths with darker coloring thrived in polluted areas during the Industrial Revolution.
• Dark-furred rock pocket mice became more prevalent on lava flows.
• Fitness measures an organism's ability to survive, reproduce, and pass on its genes.

Evidence of Evolution

• Five categories support evolution: fossils, biogeography, embryology, genetics, and anatomy.
• Fossils display transitional forms linking ancestors to modern species.
• Biogeography studies the geographic distribution of species, such as unique species in isolated regions.
• Similar embryonic stages in different species suggest common ancestry.
• DNA similarities across species indicate shared ancestry.

Anatomy

• Homology: Similar structures with different functions (e.g., bat wings, whale flippers, and human arms).
• Analogy: Similar functions but different origins (e.g., wings of birds and insects).
• Vestigial structures: Reduced or unused features (e.g., human appendix).

Evolution of Populations

• Genetic diversity increases a population's ability to adapt to changing environments.
• The formula ( p + q = 1 ) represents allele frequencies, where ( p ) and ( q ) are dominant and recessive allele frequencies.
• As an example, for 50 FF, 50 Ff, 50 ff frequency of ( F ) calculates to ( \frac{100}{300} = 0.33 ).
• Mutations and sexual reproduction (gene recombination) are the source of variation.
• Higher variation in allele frequency means greater genetic diversity.

Patterns of Selection

• Normal Distribution: Data points are clustered around the mean (bell shaped).
• Directional Selection: One extreme phenotype is favored.
• Stabilizing Selection: Average phenotype is favored, extremes are selected against.
• Disruptive Selection: Both extremes are favored, average phenotypes are selected against.

Factors Contributing to Evolution Besides Natural Selection

• Mutation: Introduce new genetic variations
• Gene Flow: Movement of genes between populations
• Genetic Drift: Random changes in allele frequencies
• Sexual Selection: Preferences for certain traits in mates
• Recombination: Shuffling of genes during sexual reproduction

Other Evolutionary Concepts

• Gene flow transfers genetic material between populations, introducing new alleles and increasing diversity.
• Genetic drift signifies random allele frequency changes, causing significant evolutionary shifts in small populations.
• The bottleneck effect reduces population size drastically, losing genetic diversity.
• The founder effect establishes a new population from a small group, limiting genetic variation.

Speciation

• Speciation is the process by which new, distinct species arise from existing species.
• Reproductive isolation prevents gene flow, which can lead to speciation.
• Populations diverge genetically over time, evolving into separate species when interbreeding ceases.

Isolation Examples

• Geographic isolation: Physical barriers separate populations.
• Temporal isolation: Populations reproduce at different times.
• Behavioral Isolation: Differences in mating behaviors prevent interbreeding.
• Speciation occurs when gene flow is interrupted.
• Populations evolve independently, allowing new species to form over time.

Convergent vs. Divergent Evolution

• Convergent Evolution: Unrelated species evolve similar traits in similar environments, which are known as analogous traits.
• Divergent Evolution: Related species evolve different traits in different environments, which are known as homologous traits.

Catastrophism vs. Gradualism

• Catastrophism: Sudden, short-term events cause major changes.
• Gradualism: Slow, continuous processes cause gradual changes.
• Punctuated equilibrium is stability interrupted by rapid changes; radiation of new life follows extinction events.

Origins of Life

• Formation of Organic Molecules: Simple molecules combined to form complex organic molecules.
• RNA as the 1st Hereditary Material: RNA could store genetic information and catalyze chemical reactions.
• Formation of Cellular Membranes: Lipid molecules formed membranes, creating cell-like structures.
• The Miller-Urey Experiment tested organic molecule formation from inorganic precursors under early Earth conditions.
• Fossil Stromatolites are formed by layers of cyanobacteria and contributed to atmospheric oxygen production.
• Endosymbiosis explains eukaryote formation, chloroplasts and mitochondria have their own DNA similar to prokaryotes.

Primate Evolution

• Primate Categories: Lemurs, Tarsiers, Anthropoids, Hominoids, Hominins.
• A linear depiction of human evolution is incorrect because it is a branching process.
• Comparing DNA sequences determines evolutionary relationships.

Extinct Hominins

• Australopithecus afarensis: Early hominin with ape-like and human-like traits.
• Homo habilis: Known for using stone tools.
• Homo neanderthalensis: Closely related to modern humans, with robust builds and large brains.
• The human brain has increased in size and complexity, leading to advanced cognitive abilities.
• The FOXP2 gene is associated with language and speech development in Homo sapiens.