Origins of Evolution

  • Extinction was a common occurrence

  • Georges Cuvier (1769-1832)

    • fossils in strata closer to the surface looked more like extant taxa than fossils in deeper strata

    • catastrophism=layers represent catastrophes causing species to die off

  • James Hutton (1726-1797) + Charles Lyell (1797-1875)

    • Gradualism (Hutton) + Uniformitarianism (Lyell) = slow, constant geological processes have been persisting all throughout Earth’s history

    • influences Darwin because he thought if these slow geological processes have been occurring, maybe evolution is the same way

  • Jean-Baptiste de Lamarck (1744-1829)

    • 1st person to propose a mechanism for evolution

    • individuals match their environment

    • traits change due to use and disuse

    • traits that are acquired during an organism’s lifetime are passed down to their offspring

    • organisms have an innate drive to be more complex

  • Individuals do not evolve or decide to change genetic structure

  • Charles Darwin (1808-1882)

    • geologists Hutton and Lyell influenced him

    • Because Earth is so old, if these slow processes have been happening over time, there would be substantial change to organisms

    • Species evolve

    • Influenced by Thomas Malthus’ economics when it came to population growth

  • Voyage of the Beagle (1831-1836)

    • John Edmonstone- a Black man from Guyana who taught Darwin how to do taxidermy

      • allowed Darwin to preserve the birds he studied

Concepts of Natural Selection

  • Selective Pressure- a nonrandom influence that affects who survives or reproduces

    • individuals w/in a population are genetically different from one another

    • this causes selective pressure (depending on the traits they have)

    • which causes differential survival

  • Fitness- the contribution an individual makes to the gene pool of the next generation

    • fittest individual has the greatest % of alleles in the next generation

    • individuals who die young but reproduce a lot before they die can have high levels of fitness

    • Ways to maximize fitness:

      • Don’t die b/4 reproducing

      • Maximixe output of viable offspring

        • mass reproduction

        • make yourself seem more attractive to possible mates

  • Differential Reproductive Success- individuals w/ different genetic traits/adaptations have diff success in reproducing

    • those more suited for the environment leave more offspring→higher fitness

    • adaptations= inherited traits that help an individual survive+reproduce

  • For every observable pattern, there is an inferred process

    • Observable pattern: varied beak shapes match food source

    • inferred process: beak shapes are inherited adaptations that promote fitness→natural selection for this beak shape

    • Process: gene variation exists→differential reproductive success→gene frequencies change

  • Descent w/ Modification= diversity of life

    • connections through a common ancestor

    • visualized using phylogenetic trees

    • extant = those that still exist, reach current day/tip of the phylogenetic tree

    • extinct = dead, don’t reach the tip

  • Artificial selection= human interest involved

Key Points of Natural Selection

  1. Individuals DO NOT evolve

  2. Traits must be heritable

  3. Favorable traits depend on environmental context

  4. NOT goal oriented→evolution is not intentional, it only happens because of increased fitness in the surviving indivuals of the population