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Biocomplexity - Background to Evolution

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Lecture 4: Background to Evolution

Artificial Selection

− Artificial selection (or selective breeding) describes intentional breeding for certain traits, or combination of trait.

− Artificial selection IS evolution

Natural Selection

− Variations of conspecific individuals are genetically based.

− Some traits are better at surviving than others, increasing changes of surviving and reproducing.

− Offspring than inherit the traits of their successful parents.

− Variation is random, but selection is directional

o E.g. resistance to insecticides or antibiotics.

Selection Pressure

− Certain characteristics increase the fitness over other members of its species.

o Sexual selection, mimicry, predation.

Process of Evolution

− Two events are involved in evolutionary divergence among organisms.


− The events that modify a species WITHOUT causing new species to originate.

o Much like that of adaption.


− The events that lead to the origin of new taxa.

− Think of it as: Speciation = branching, while phylesis = branch lengths

− The biological changes during speciation are constrained by pre-existing features.

− Mot traits have clearly risen from pre-exiting traits that have been modified to perform a new function.

The Process of Speciation

− Remember that:

o Species - a group of interbreeding populations that share a gene pool.

o Gene flow - is the migration of individuals or genes among populations.

− Over time, isolation may occur which leads to rising differences between populations and they begin to accumulate.

o The separated populations experience different mutation and environments.

o The separation leads to the differences not being 'shared' or blended in the gene flow.

− Speciation completes hen the growing differences become great enough to prevent interbreeding.

− Reproductive Isolation Mechanisms prevent interbreeding and keep species apart even when they co-habit in the same place.

How does a species arise?

Sympatric Speciation

− Occurs WITHOUT physical separation of the gene pools.

Allopatric Speciation

− Requires a physical barrier within the gene pool

Parapatric Speciation

− Occurs



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