Evolution, Population Genetics, and Speciation: Study Notes (Ch. 22–25)

Ch. 22: Evolution and the Origin of Species

Lamarck and Acquired Characteristics

Jean-Baptiste Lamarck proposed that organisms could pass on traits acquired during their lifetime to their offspring. This idea, known as the inheritance of acquired characteristics, has been disproven by modern genetics.

• Acquired characteristics: Traits gained during an organism's life (e.g., muscle strength) are not inherited by offspring.

• Example: Lamarck suggested giraffes' long necks resulted from stretching and were passed down. This is incorrect.

Darwin and the Origin of Species

Charles Darwin's work established the theory of evolution by natural selection, explaining how species change over time.

• Natural selection: The process by which organisms with favorable traits are more likely to survive and reproduce.

• Common descent: Evidence for evolution includes homologous structures, fossil records, and biogeography.

Homologous Structures

Homologous structures are anatomical features in different species that share a common ancestry, even if they serve different functions.

• Example: The forelimbs of humans, cats, whales, and bats.

Microevolution vs. Macroevolution

Evolutionary change can occur on different scales:

• Microevolution: Small-scale changes within a population (e.g., allele frequency shifts).

• Macroevolution: Large-scale changes that result in new species or groups.

Evidence for Evolution

• Fossil record: Shows progression of life forms; oldest known fossils are bacteria.

• Biogeography: Distribution of species supports common descent.

• Homologous and analogous structures: Homologous = shared ancestry; analogous = similar function, different ancestry.

• Vestigial organs: Structures with no current function (e.g., human appendix).

• Molecular biology: DNA and protein sequence similarities indicate relatedness.

Ch. 23: Population Genetics and Microevolution

Gene Pool and Population Genetics

The gene pool is the total collection of genes in a population. Population genetics studies how allele frequencies change over time.

• Sexual dimorphism: Differences in appearance between males and females (e.g., lion manes).

Hardy-Weinberg Principle

The Hardy-Weinberg equation predicts allele and genotype frequencies in a non-evolving population.

• Equation: $p^2 + 2pq + q^2 = 1$ and $p + q = 1$

• Conditions: Large population, no mutation, no migration, random mating, no natural selection.

Causes of Microevolution

• Mutation: Source of genetic variation.

• Genetic drift: Random changes in allele frequencies (e.g., bottleneck and founder effects).

• Bottleneck effect: Population size drastically reduced by events (e.g., natural disasters).

• Founder effect: New population started by a small group, leading to different allele frequencies.

• Gene flow: Movement of alleles between populations.

Natural Selection and Modes

• Stabilizing selection: Favors intermediate phenotypes.

• Directional selection: Favors one extreme phenotype.

• Diversifying/disruptive selection: Favors both extremes over intermediates.

Ch. 24: Speciation and Macroevolution

Anagenesis vs. Cladogenesis

• Anagenesis: Gradual evolution of a species into a new form without branching.

• Cladogenesis: Branching evolution, resulting in new species and increased diversity.

Reproductive Isolation

Prezygotic and postzygotic barriers prevent species from interbreeding.

• Prezygotic barriers: Prevent mating or fertilization (e.g., habitat, temporal, behavioral, mechanical, gametic isolation).

• Postzygotic barriers: Prevent hybrid offspring from surviving or reproducing (e.g., reduced hybrid viability or fertility).

Allopatric vs. Sympatric Speciation

• Allopatric speciation: Geographic isolation leads to new species.

• Sympatric speciation: New species arise within the same geographic area.

Punctuated Equilibrium

Evolutionary change occurs in rapid bursts, followed by periods of stability.

Adaptive Radiation

Rapid evolution of many species from a common ancestor, often following environmental changes (e.g., Galápagos finches).

Ch. 25: Systematics and Taxonomy

Binomial Nomenclature

• Two-part naming system: Genus (capitalized, italicized) and species (lowercase, italicized).

• Example: Homo sapiens

Convergent and Divergent Evolution

• Convergent evolution: Unrelated species evolve similar traits (e.g., bird and bat wings).

• Divergent evolution: Related species evolve different traits.

• Analogous structures: Similar function, different ancestry.

Criteria for Taxonomy

• Classification based on morphology and phylogeny (evolutionary relationships).

Fossils

• Remains or traces of ancient organisms found in rock, amber, or tar.

Key Evolutionary Principle

• Mutations occur in individuals, but evolution occurs in populations and species.