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JEAN BAPTISTE LAMARCK

EVOLUTIONARY THEORY

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JEAN BAPTISTE LAMARCK

B:1774 D:18292 theories of how organisms changed over

time1. Acquired characteristics2. Law of use and disuseTheories were determined to be incorrect

BUT he was the first to publicly state that evolution of organisms occurs

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CHARLES DARWIN

EVOLUTIONARY THEORY

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CHARLES DARWIN

B:1809 D:1882Man most famously credited for

“discovering” evolution5 basic principles of natural selection1. Individuals of species vary2. Some variations heritable3. More born than can survive4. Competition for resources5. Most fit individuals survive to reproduce

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NATURAL SELECTION

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NATURAL SELECTION

Darwin’s explanation for how changes in organisms occur

Nature is acting upon the phenotype of each individual organism; a favorable phenotype increases survival in the environment

Organisms must adapt, migrate or dieDarwin’s theory revolves around the

reproductive success of organisms with favorable phenotypes

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MUTATIONS

VARIATION

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MUTATIONS

Driving force for evolutionOrigin source for new alleles in a populationRandom changes in the genotypes of

members of a populationFavorable/useful mutations increase

organism’s chances for survivalMutations are rare so the effects are rarely

seen in a specific populationCumulatively, mutations are why we are

humans and not house plants

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VARIATION FROM RECOMBINATION

VARIATION

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VARIATION FROM RECOMBINATION

Genetic variation by mutation alone tends to be a slow process (unless you are a bacteria)

Genetic recombination through sexual reproduction speeds up this process dramatically

Mechanisms:1. Crossing-over: exchange of genes between

homologous chromosomes2. Independent assortment: genes segregate

independently of each other

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VARIATION FROM MIGRATION

VARIATION

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VARIATION FROM MIGRATION

Members of different populations of the same species are able to interbreed and produce fertile offspring

As members migrate from one population to another, they take their specific genotypes with them

Over time, this causes changes in the gene frequencies of the gene pools of each population

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VARIATION FROM MIGRATION

Examples of variations in populations:1. Morphological: differences in body shapes

and colors 2. Chromosomal: in some species, there can

be a difference in chromosome number and shape; common in plants and insects

3. Protein: amino acid substitutions that do not affect protein structure