Key Terminology
Evolution: Heritable change in characteristics of a population over generations.
Microevolution: Small-scale changes in allele frequencies within a population.
Macroevolution: Large-scale formation of new species.
Species: Group of organisms that share a distinctive form.
Population: Members of the same species in the same area that can interbreed.
Important Scientists
John Ray (1600s): Developed an early classification system, introduced the species concept.
Carl Linnaeus: Expanded Ray’s work, created binomial nomenclature (e.g., Homo sapiens).
George Buffon (1700s): Suggested species change over time.
Jean-Baptiste Lamarck: Proposed species evolve by adapting to their environment over generations.
Lamarck’s Theory (Incorrect)
Organisms change behavior in response to environment → Traits modify → Passed to offspring.
Example: Giraffes stretch necks → Longer necks inherited.
Influence on Evolutionary Thought
Uniformitarianism (Geology): Earth changes gradually over time (older than 6,000 years).
Thomas Malthus (Economics): Not all individuals survive and reproduce due to competition.
Charles Darwin
Developed natural selection theory.
Influenced by:
Voyage on HMS Beagle (1831-1836).
Galápagos finches (variation in beak shape).
"On the Origin of Species" (1859): Evolution by natural selection.
Darwin’s Theory of Evolution
Variation in Traits – Inherited differences exist in a population.
Natural Selection – Individuals with favorable traits survive and reproduce, passing traits to offspring.
Genetic Variation & Mutations
Source: Random mutations, recombination, and random mating.
Importance: Enables adaptation and survival.
Darwin vs. Lamarck on Elephant Trunks:
Lamarck: Elephants stretched trunks → Offspring inherited longer trunks.
Darwin: Elephants had different trunk lengths → Those with longer trunks survived and reproduced.
Beak Depth on Daphne Major
Medium ground finches studied for 40+ years as a model of natural selection.
Beak depth is heritable (measured in parents & offspring).
1977 drought: Fewer small seeds → finches ate larger, harder seeds.
1978 offspring had larger beaks than 1976 → evidence of natural selection.
Selective Breeding (Artificial Selection)
Humans select desirable traits in domesticated species.
Differs from natural selection: Parents chosen based on phenotype.
Examples: Darwin’s pigeons, wild mustard breeding.
Biogeography
Study of species distribution.
Isolated regions evolve unique species (e.g., endemic species).
Example: Island fox on Channel Islands evolved from mainland gray fox.
Australia: Home to marsupials due to geographic isolation.
Convergent Evolution
Unrelated species evolve similar traits due to similar environments.
Traits = analogous structures (not due to shared ancestry).
Example: Fishapod, whale evolution.
Homology (Common Ancestry)
Anatomical Homology
Vertebrate forelimbs share a common structure but serve different functions.
Vestigial structures: No function but resemble ancestral traits.
Developmental Homology
Similar embryonic features in different species (e.g., human embryos have gill ridges and tails).
Molecular Homology
DNA similarities indicate common ancestry.
Shared biochemical pathways across species.
Genes more similar between closely related species.
Homologous Genes
Genes from the same ancestral gene.
Orthologs: Same gene in different species.
Paralogs: Gene duplications within a species (e.g., globin gene family).
Horizontal Gene Transfer
Genes transferred between organisms (not inherited from parents).
Occurs in bacteria and across species.
Evolution at the Genome Level
Chromosome structure & number changes can drive speciation.
Affects ability of species to interbreed.