Evolution (I)

Alfred Russel Wallace

“On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life”(1859)

Darwin’s Theory of Evolution

• Variation: There is variation among

the individuals of most natural populations

• Inheritance: Some of that variation is inherited

• Competition: Populations tend to produce more offspring than the environment can support

• Survival of the Fittest: Those individuals whose traits best adapt them to the environment will survive better and leave more offspring than those with less adaptive traits

Key forces which influencethe evolution of species

• Environmental changes (e.g. geographic isolation of marsupials)

• Random factors (e.g. Genetic drift due to the founder effect)

CONVERGENT

EVOLUTION

•Different species come to resemble each other due to the similarities in their habitats (ecological niches)

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Analogous structures

• Structures that evolved independently but are similar in their form because of a similar function

Analogous structure

Homologous structures

• Structures that share the same origin (e.g. ancestral mammalian limb) but serve different function in different species

DIVERGENT

EVOLUTION

• continued accumulation of differences between or among species, attributable to adaptive radiation

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VESTIGIAL ORGAN: no longer useful but still retained

A vestigial structure in the skeleton of a baleen whale.The pelvic bones have no apparent function.