Natural Selection and Evolution

Natural Selection

• Evolution represents changes in a population over time
• Natural selection occurs with populations, in terms of individuals
• Charles Darwin's work is the basis for much understanding of evolution

Darwin's Observations

• Species produce more offspring than can survive
• Offspring compete for limited resources
• Organisms vary in every population
• Evolutionary fitness is measured by reproductive success
• The fittest offspring with favorable traits are the most likely to survive and reproduce
• The most likely traits are passed to subsequent generations
• Fitness varies based on biotic and abiotic factors
• Different genetic variations can be selected for in different generations

Lamarck and the Long Necks

• Jean-Baptiste de Lamarck proposed this theory of evolution
• Acquired traits are inherited and passed on

Evidence for Evolution

• Paleontology reveals the major lines of evolution
• Fossils can be dated by the age of the rocks where they are found, rate of decay of isotopes like carbon-14, and geographical data
• Biogeography studies the distribution of flora and fauna and finds related species in separated regions
• Embryology studies the development of organisms, vertebrates show fishlike features called gill slits
• Morphological homologies studies the anatomy of various animals, showing similar structures serve different functions
• Homologous structures point to a common ancestor, analogous structures evolved independently
• Molecular biology's compelling proof is similarity at the molecular level
• Evolution is constantly occurring, demonstrated by changes in DNA and fossil records

Common Ancestry

• Some original life-form is the common ancestor to all life
• Phylogenetic trees or cladograms study relationships between organisms
• Phylogenetic trees use fossil/molecular records, phylogenetic trees are drawn with different distances making the look different than even spaced cladograms
• Phylogenetic trees begin with a common ancestor and branch out, forks are called common ancestor nodes

Genetic Variability

• Differences in people are known as genetic variability
• Natural selection acts only when individuals have evolutionary fitness, more variations make a trait more likely to be a "lifesaver"
• Genetic variation is the foundation of evolution

The Peppered Moths

• A 1:1 phenotype ratio was observed until air pollution changed the environment
• The gene pool reached 90% dark alleles and only 10% light alleles
• Light moths were easily spotted, dark moths multiplied quickly

Causes of Evolution

• Natural selection requires genetic variation and environmental pressure
• Biotic and abiotic factors affect the direction of evolution
• Mutations can be passed on unless lethal before reproduction
• Survival of the fittest = better reproduction = evolutionary fitness
• Females choosing mates is sexual selection
• Genetic drift, like the bottleneck effect/founder effect, changes population genetics without natural selection
• Gene flow occurs through migration between populations
• Stabilizing selection and disruptive selection are types of selection
• Stabilizing selection eliminates extreme traits
• Artificial selection is human-driven

Species Population

• Reproductive isolation is required to become different species
• Divergent evolution occurs with different variation and environmental pressures of isolated species
• Punctuated equilibrium is divergent evolution after stasis
• Pre-zygotic barriers prevent fertilization
• Post-zygotic barriers relate to hybrid offspring infertility
• Convergent evolution leads to similar traits in unrelated species due to similar selective pressures
• There are two types of speciation: allopatric and sympatric
• Allopatric speciation separates a population by geographic barriers

Genetics

• Mendel’s laws extend to the population level
• The Hardy-Weinberg law states, relative genotype frequencies are constant
• p² + 2pq + q² = 1: p² represents homozygous dominants, 2pq represents heterozygotes, q² represents homozygous recessives

Hardy-Weinberg Equilibrium (Five Conditions)

• Consequences occur within a population if the proceeding 5 conditions are unmet
• Small populations are more susceptible to random environmental impact
• Mutations introduce new alleles, disturbing genetic equilibrium
• Immigration/emigration brings/removes alleles
• Non-random mating selects mates based on traits
• Natural selection adapts organisms to their environment, favoring alleles

Origins of Life on Earth

• Alexander Oparin and J. B. S. Haldane proposed the primitive atmosphere contained inorganic molecules
• Contained methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O)
• There was almost no free oxygen (O2)
• Stanley Miller and Harold Urey created primitive Earth; the gases in a flask were struck with electrical charges, and organic compounds appeared
• The original life-forms were RNA, which is termed the RNA-world hypothesis

Proofs of Evolution

• Homologous features: shared physical features from evolutionary history (divergent evolution)
• Vestigial structures: reduced/nonfunctional features with little present purpose
• Fossil records: preserved remains/traits from the past
• Observable differences/direct observation: differences in present-day organisms vs organisms of the past
• Embryo similarity: different species show multiple similarities in the embryo of the offspring when developing

Hardy Weinberg Equilibrium

• To achieve Hardy Weinberg Equilibrium requires:
• No natural selection
• Random mating
• No gene flow
• No genetic drift
• A large population

Sympatric Speciation

• Includes:
• Habitat differentiation
• Sexual selection
• Polyploidy

Post Zygotic Barriers

• Includes:
• Viability: reduced hybrid viability
• Fertility: reduced hybrid fertility
• Breakdown: hybrid breakdown

Prezygotic Barriers

• Includes:
• Habitat isolation
• Temporal Isolation
• Behavioral Isolation
• Meeh Isolation
• Gametic Isolation
• Fermentation