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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.