BIOL1100 - Evolution Study Notes

Salamander Speciation

  • Speciation Type: Allopatric speciation

  • Barrier: Physical/geographical barrier (Central Valley)

  • Process: Cladogenesis (splitting into two lineages)

Effects of Climate Change

  • Gene Flow: Increases with interbreeding

  • Evolution Impact: May reduce genetic differences, slow or reverse speciation

Natural Selection Mechanisms

  1. Stabilizing Selection

    • Favorable conditions for intermediate phenotype

  2. Directional Selection

    • Favorable conditions for one extreme phenotype

  3. Disruptive Selection

    • Favorable conditions for both extreme phenotypes

Derived Characters by Group

  • Humans: Large brain, bipedalism, flat face, complex language

  • Primates: Opposable thumbs, flexible shoulders, forward-facing eyes

  • Anthropoids: Larger brain to body ratio, reduced snout

  • Tetrapods: Four limbs, lungs, vertebral regions

Prezygotic vs. Postzygotic Barriers

  • Prezygotic Barriers:

    • Habitat isolation

    • Temporal isolation

    • Behavioral isolation

    • Mechanical isolation

    • Gametic isolation

  • Postzygotic Barriers:

    • Reduced hybrid viability

    • Reduced hybrid fertility

    • Hybrid breakdown

Hominin Species Features

  • Closest Relatives: Homo neanderthalensis, Homo denisovans

  • Early Hominins: Sahelanthropus tchadensis

  • Bipedal Evidence: Ardipithecus ramidus, Australopithecus sediba

  • Notable Fossil: Australopithecus afarensis ("Lucy")

  • Potential Tool User: Australopithecus garhi

  • Earliest Homo Genus: Homo naledi

  • Extensive Tool Use: Homo habilis

  • Migration Out of Africa: Homo erectus

  • "Hobbit" Traits: Homo floresiensis

Hybrid Zone Outcomes

  1. Reinforcement: Less fitness of hybrids, barrier reinforced

  2. Stability: Constant hybrids, no merging

  3. Fusion: Hybrids survive and reproduce, merging species over time