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 influence the 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) * *

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

Analogous structure

Homologousstructures 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 * *

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.