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Evolution: Summary Notes
Introduction to Evolution Evolution is the process through which the characteristics of
species change over many generations. It explains the diversity of life on Earth, showing how
current species have evolved from common ancestors over long periods.
1. Foundations of Evolutionary Theory
Charles Darwin and Natural Selection: Darwin’s theory of natural selection posits
that individuals with traits better suited to their environment are more likely to survive
and reproduce. These advantageous traits become more common in the population
over generations.
Alfred Russel Wallace: Independently conceived the theory of evolution by natural
selection, emphasizing environmental pressures that could lead to the survival of the
fittest.
2. Mechanisms of Evolution
Natural Selection: Drives evolutionary changes by favoring individuals who are better
adapted to survive and reproduce in their environment.
Mutation: Random changes in DNA that can lead to new traits. Mutations can be
beneficial, neutral, or harmful.
Gene Flow: Also known as migration, is the transfer of genetic material between
populations of the same species, which can introduce new genes into a population.
Genetic Drift: Random changes in allele frequencies which can cause genes to
become more or less common in a population. This is more pronounced in small
populations.
3. Types of Natural Selection
Directional Selection: Favors phenotypes at one extreme of the trait spectrum.
Stabilizing Selection: Favors intermediate variants by acting against extreme
phenotypes.
Disruptive Selection: Favors individuals at both extremes of the phenotypic range.
4. Evidence for Evolution
Fossil Record: Provides chronological evidence of past life forms and their evolution
over time.
Biogeography: The study of the distribution of species and ecosystems in geographic
space and through geological time.
Comparative Anatomy: The comparison of body structures between different species
illustrates similarities that suggest common descent.
Molecular Biology: DNA and the genetic code reflect the shared ancestry of life. DNA
comparisons can show how related species are and help map out evolutionary trees.
5. Speciation
Allopatric Speciation: Occurs when biological populations of the same species
become isolated, leading to genetic divergence.
Sympatric Speciation: Occurs without geographic separation and can result from
polyploidy, natural selection, or hybridization.
6. Evolutionary Theories Beyond Darwin
Punctuated Equilibrium: Proposed by Stephen Jay Gould and Niles Eldredge,
suggests that species experience long periods of little evolutionary change (stasis)
punctuated by brief periods of rapid change during speciation.
Neutral Theory of Molecular Evolution: Posits that most evolutionary changes at the
molecular level are not caused by natural selection but by genetic drift of mutant alleles
that are neutral.
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7. Evolutionary Impact on Ecology and Modern Science
Coevolution: The process by which two or more species evolve in response to mutual
selective pressures.
Evolutionary Medicine: Applies concepts of evolutionary biology to understand health
challenges such as pathogens’ resistance to drugs.
Conservation Biology: Uses evolutionary principles to understand the effects of
genetic diversity and population structure on species survival.
Conclusion Evolutionary biology not only illuminates the history of life on Earth but also
enhances our understanding of current biological processes and challenges. It is foundational
in fields ranging from medicine to environmental conservation.
