What is evolution?

– Evolution is the change of alleles/genes in a gene pool of a population.

– As such a new species arose from a pre-existing species.

– All species have evolved from one common ancestral type.

– Natural selection provides the mechanism for one species to change into another.

– The gradual change of living things from one form into another over the course of time, the origin of species and lineages by descent of living forms from ancestral forms, and the generation of diversity.

Lamarck’s Theory (earlier theory, proven wrong later by scientists)

– Evolution occurred through the inheritance of acquired traits.

– Environmental pressure on an organism produces the specific needs in the organism to develop certain structures, characteristics or adaptations.

– The organism will act to fulfill its specific need.

– As a response to its actions, adaptations occur to the organism according to its specific need.

– The adaptations are transmitted from generation to generation.

Example:

– Giraffes with long necks resulted when the ancestors of the present giraffes ate leaves of trees instead of grass.

– To reach the leaves high up the trees, they have to stretch their necks.

– Continuous stretching of the giraffe’s neck produces giraffe with long necks.

– The longer necks that developed were then inherited by the giraffes’ descendants.

Lamarck’s theory is not accepted because the acquired characteristics cannot be inherited.

The acquired traits only involve changes in the phenotype, while the genootype of an organism is not affected.

Darwin-Wallace’s Theory

– Evolution occurs through natural selection.

– Natural forces select for the survival of organisms that are best fit in an environment.

– A population has high biotic potential produces more progeny than can be accommodated by the environment.

– An environment has a specific carrying capacity and can only support a specific number of organisms.

– Members of the population compete for survival.

– The members in a species show variations.

– Progeny that have the phenotype that is best adapted to the environment have more chance to survive, reproduce and to pass genes to offspring.

– Progeny with phenotypes that are not suited to the environment will die before reaching the reproductive age.

– Over time, the frequency of phenotype that gives the best adaptations to survive in an environment increases.

– Survival of the fittest occurs.

Example:

– In a population of giraffes, there is variation for the length of giraffe’s neck.

– Giraffes with longer neck are selected by the environment as the giraffes are able to reach leaves on taller trees.

– Longer neck giraffes obtain higher food supply compared to giraffes with shorter neck.

– Giraffes with long necks survive and have higher chance to reproduce, passing gene for long neck to offspring.

– Giraffes with shorter neck die at a younger age as it obtains less food supply, and lower chance to reproduce to pass genes to the next generation.

– The process is repeated over many generations to produce modern giraffes with long necks.

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