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Evolution. How Populations Evolve. Voyage of the Beagle. Jean Baptiste Lamarck. Charles Lyell. Artificial Selection. Artificial Selection. Natural Selection. Darwin saw natural selection as the basic mechanism of evolution

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How Populations Evolve

Jean baptiste lamarck
Jean Baptiste Lamarck

Natural selection
Natural Selection

  • Darwin saw natural selection as the basic mechanism of evolution

    • As a result, the proportion of individuals with favorable characteristics increases

    • Allele frequencies (and therefore phenotypes within a population) gradually change over time


African wilddog





Thousands tomillions of yearsof natural selection

Ancestral canine

Figure 13.4C



Chromosome with geneconferring resistanceto insecticide

Additionalapplications of thesame insecticide willbe less effective, andthe frequency ofresistant insects inthe populationwill grow


Figure 13.5B

Ammonite casts fossilized leaf
Ammonite casts; Fossilized leaf natural selection in action


Biogeography natural selection in action

Comparative embryology
Comparative Embryology natural selection in action

Comparative embryology1
Comparative Embryology natural selection in action

Molecular biology
Molecular biology natural selection in action

Population genetics and modern evolutionary synthesis theory
Population Genetics and Modern Evolutionary Synthesis Theory different environments

  • Population genetics

    • Studies how populations change genetically over time

  • The modern evolutionary synthesis theory

    • Connects Mendelian Inheritance, Darwin’s theory with population genetics

  • Gene pool

    • Is the total collection of genes in a population at any one time

  • Microevolution

    • Is a change in the relative frequencies of alleles in a given gene pool


Gene pool in a different environmentsnonevolving population remains constant over generations.

Hardy weinberg principle
Hardy-Weinberg different environmentsPrinciple

  • States that allele and genotype frequency in a population remain constant (equilibrium) – from generation to generation unless an outside influence disturbs the balance.

Hardy weinberg principle1
Hardy-Weinberg different environmentsPrinciple

  • Must satisfy five conditions

    • The population is very large

    • The population is isolated

    • Mutations do not alter the gene pool

    • Mating is random

    • All individuals are equal in reproductive success

Hardy weinberg equation
Hardy-Weinberg Equation different environments

  • p2 + 2pq + q2 = 1

  • p + q = 1


  • p is frequency of the dominant allele; q is the frequency of the recessive allele

  • p2 is the frequency of the homozygous dominant genotype

  • 2pq is the frequency of the heterozygous genotype

  • q2 is the frequency of the homozygous recessive genotype


Other contributors to evolution include
Other contributors to evolution include science

  • Genetic Drift – change in the relative frequency of an allele

    • Bottleneck effect

    • Founder effect

  • Gene Flow – movement of alleles from one population to another

    • Emigration/immigration

Founder effect
Founder Effect science

  • Loss of genetic variability when a new population is established by a very small number of individuals from a larger population.

Founder effect1
Founder Effect science

Island of Krakotoa, 1883


Variation and natural selection

0 science


  • Variation is extensive in most populations

    • Many populations exhibit polymorphism

      • Different forms of phenotypic characteristics

      • Functions to retain variety of morphs in a population living in a varied environment

Polymorphism science


0 science

  • Populations may also exhibit geographic variation

    • Variation of an inherited characteristic along a geographic continuum

Natural selection can alter variation in a population in three ways
Natural selection can alter variation in a population in three ways

  • Stabilizing selection

  • Directional selection

  • Disruptive selection

Modes of selection
Modes of Selection three ways


Figure 13.17B three ways

Figure 13.17A


Sexual selection may produce sexual dimorphism

  • Sexual selection leads to the evolution of secondary sexual characteristics

    • Which may give individuals an advantage in mating

Processes and mechanisms of evolution
Processes and Mechanisms of Evolution three ways

  • Adaptation

  • Genetic drift

  • Gene flow

  • Mutations

  • Natural selection

  • Speciation