Evolutionary trends

By Martin Samaj

Rates of evolution

• Gradualism – claims that evolution proceeds very slowly, large changes can occur over long periods of time

• This theory does not fit with fossil record, which show periods where the evolutionary rate was stable, followed by a period of rapid changes

• These changes in evolutionary rates may be due to the environmental changes which would require the species to adapt to these new conditions

• This view of the pace of evolution is called punctuated equilibrium

Adaptive radiation

• When each species evolves in a different way, we call it divergent evolution

• Adaptation to different ecological roles avoids competition among species

• If species in a group deviate rapidly it is called adaptive radiation

• Example: when a group has a characteristics that gives it a competitive advantage over existing species

• Mammals also demonstrate adaptive radiation – the pentadactyl limb

Transient polymorphism

• Population in which there are two alleles of a gene in the gene pool is polymorphic

• If one allele is gradually replacing the other the population shows transient polymorphism

• The peppered moth is an example of this

Convergent evolution

• Living organisms often find the same solutions to particular physiological problems

• If natural selection acts the same also in other parts of the world, species can become remarkably different despite not being closely related at all

• This is called convergent evolution• Instead of closely related species

showing striking differences, unrelated species show striking similarities

Balanced Polymorphism

• Sometimes alleles of gene can persist indefinitely in the gene pool of a population

• This is called balanced polymorphism

• The most researched example of this would be sickle anemia

• Heterozygous individuals do not develop sickle cell anemia and are resistant to sickle cell anemia

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