Evolution
Introduction to Evolution Evolution explains the diversity of life and unites all fields of biology. It is
defined as a change in allele frequencies in populations over generations. Charles Darwin and Alfred
Russel Wallace proposed natural selection as a driving mechanism.
Natural Selection Natural selection acts on heritable variation. Individuals with advantageous traits
survive and reproduce more, passing on those traits. Over time, populations adapt to their
environments. Peppered moth coloration during the Industrial Revolution is a classic example of
selection in action.
Evidence for Evolution Multiple lines of evidence support evolution: - Fossils show transitional forms
and gradual change. - Comparative anatomy reveals homologous structures with shared ancestry. -
Embryology demonstrates similar developmental stages across species. - Molecular biology shows
conserved DNA and protein sequences.
Microevolutionary Processes In addition to natural selection, genetic drift, gene flow, and mutation alter
allele frequencies. - Genetic drift has strong effects in small populations (founder effect, bottleneck
effect). - Gene flow introduces new alleles between populations. - Mutations provide raw material for
evolution.
Speciation Speciation is the formation of new species. - Allopatric speciation occurs when geographic
barriers separate populations. - Sympatric speciation occurs without physical separation, often driven
by niche differentiation or polyploidy in plants. Adaptive radiation, such as Darwin’s finches,
demonstrates rapid diversification.
Macroevolution and Extinction Macroevolution refers to large-scale patterns, including mass extinctions
and radiations. The fossil record documents five major mass extinctions, with the most recent
(Cretaceous) leading to the rise of mammals. Evolutionary developmental biology (evo-devo) explores
how changes in developmental genes shape body plans.
Modern Evolutionary Synthesis The integration of Mendelian genetics with Darwinian natural selection
forms the modern synthesis, emphasizing populations as units of evolution. Advances in molecular
genetics have expanded this framework, linking microevolutionary processes with long-term
evolutionary change.
Summary and Key Terms Evolutionary theory explains adaptation, diversity, and unity of life.
Understanding mechanisms and evidence strengthens insight into the natural world.
Key terms: evolution, natural selection, adaptation, genetic drift, gene flow, mutation, speciation,
adaptive radiation, fossil record, modern synthesis.
