CHAPTER
12 Evolution
IN THIS CHAPTER
Summary:This chapter discusses evolution and the four major modes in
which it occurs. It introduces you to the various forms of selection: natural,
directional, stabilizing, disruptive, sexual, and artificial. It discusses the two
main forms of speciation (allopatric and sympatric) and briefly touches on the
theory behind how life on this planet emerged many years ago.Key Ideas
✪The four major modes of evolution are genetic drift, gene flow, mutation,
and natural selection.
✪Natural selection is based on three conditions: variation, heritability, and
differential reproductive success.
✪There are four basic patterns of evolution: co-evolution, convergent
evolution, divergent evolution, and parallel evolution.
✪Sources of variation within populations: mutation, sexual reproduction,
and balanced polymorphism.
✪Hardy-Weinberg conditions: no mutations, no gene flow, no genetic drift,
no natural selection, and random mating.
✪Hardy-Weinberg equations: p+q= 1 and p^2 + 2pq+q^2 = 1.
✪Evidence for evolution: homologous characters, embryology, and vestigial
structures.136 ❯
KEY IDEA