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Introduction to Evolution

Natural Selection

  • Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals

  • Natural selection increases the match between organisms and their environment over time

  • If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

    • Note that individuals do not evolve; populations evolve over time

  • Natural selection can only increase or decrease heritable traits that vary in a population

  • Adaptations vary with different environments

  • Why natural selection can’t fashion perfect organisms:

    • Selection can act only on existing variations

    • Evolution is limited by historical constraints

    • Adaptations are often compromises

    • Chance, natural selection, and the environment interact

Homology

  • Homology: similarity resulting from common ancestry and is the result of divergent evolution.

  • Homologous structures: anatomical resemblances that represent variations on a structural theme present in a common ancestor

  • Convergent evolution: the evolution of similar, or analogous, features in distantly related groups

    • Convergent evolution does not provide information about ancestry

  • Analogous traits arise when groups independently adapt to similar environments in similar ways

  • Homologous genes: two genes derived from the same ancestral gene

    • Orthologs occur in separate species

  • Molecular processes reveals molecular details of evolutionary change

  • Two sequences may be similar, but not identical due to the independent accumulation of different random mutations

Darwin’s Observations of Nature

  • There’s variability in traits within a population

  • Traits are inherited from parent to child.

  • No two of the same species are exactly alike even if they have the same parents

  • All species are capable of reproducing beyond the support of the environment

  • Many offspring do not survive due to limitation of the environment.

Introduction to Evolution

Natural Selection

  • Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals

  • Natural selection increases the match between organisms and their environment over time

  • If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

    • Note that individuals do not evolve; populations evolve over time

  • Natural selection can only increase or decrease heritable traits that vary in a population

  • Adaptations vary with different environments

  • Why natural selection can’t fashion perfect organisms:

    • Selection can act only on existing variations

    • Evolution is limited by historical constraints

    • Adaptations are often compromises

    • Chance, natural selection, and the environment interact

Homology

  • Homology: similarity resulting from common ancestry and is the result of divergent evolution.

  • Homologous structures: anatomical resemblances that represent variations on a structural theme present in a common ancestor

  • Convergent evolution: the evolution of similar, or analogous, features in distantly related groups

    • Convergent evolution does not provide information about ancestry

  • Analogous traits arise when groups independently adapt to similar environments in similar ways

  • Homologous genes: two genes derived from the same ancestral gene

    • Orthologs occur in separate species

  • Molecular processes reveals molecular details of evolutionary change

  • Two sequences may be similar, but not identical due to the independent accumulation of different random mutations

Darwin’s Observations of Nature

  • There’s variability in traits within a population

  • Traits are inherited from parent to child.

  • No two of the same species are exactly alike even if they have the same parents

  • All species are capable of reproducing beyond the support of the environment

  • Many offspring do not survive due to limitation of the environment.

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