Evolution

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

  1. Variation in Traits – Inherited differences exist in a population.

  2. 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)

  1. Anatomical Homology

    • Vertebrate forelimbs share a common structure but serve different functions.

    • Vestigial structures: No function but resemble ancestral traits.

  2. Developmental Homology

    • Similar embryonic features in different species (e.g., human embryos have gill ridges and tails).

  3. 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.

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