Module 3.2: Natural Selection and Evolution
When Charles Darwin
articulated his theory of evolution by natural selection, he focused on adaptations
– the changes that enable organisms to survive in new or changing environments.
He claimed that selection for favorable adaptations allowed ancient ancestral forms
to gradually diversify into many species. Natural selection is not questionable,
but some scientists have argued that most evolutionary changes appear at the level
of the genome and are essentially random and neutral. According to the
Princeton Guide to Evolution, natural selection can occur without leading to evolution
if differences among individuals are not genetically based. The neo-Darwinian
theory of evolution argues that such a mode is possible only as neutral
evolution. The neutral theory of molecular evolution contends that at the molecular
level, most evolutionary changes and polymorphisms within species are not caused
by natural selection, but by random genetic drift. The key input required by
the neutral model is the product of the population size and the mutation rate
per generation. The Princeton Guide to Evolution states, if variation in a
population is not genetically based, then natural selection will have no
evolutionary significance.
Selection may happen in
the absence of natural selection. Scientists have been artificially selecting domesticated
plants and animals for ages. These procedures have demonstrated that species can
change dramatically through selective breeding. In artificial selection humans
select for desirable traits in agricultural products or animals, rather than
leaving the species to evolve gradually without human interference, as in
natural selection. For example, farmers and growers based on genetic changes, select
plants that produce more fruits than others to get more fruit-bearing plants, choose
plants that yield larger vegetables to get more mass of product per seed grown,
and choose plants to reproduce that can survive extreme temperatures during
droughts. Another way selection happens, in the absence of natural selection is
stated earlier in this post, genetic drift. Genetic drift changes allele
frequencies purely by chance, as random subsets of individuals are sampled to
produce the next generation.
Sources
I really liked your explanation of artificial selection and how it is used to modify organisms in the absence of natural selection. Your in-depth description of genetic drift was very well done and informative. Great post!
ReplyDelete