Question

MCAT Mini-Tutorial: Natural Selection Sub-types & Patterns

Answer 1

\({\bf{Basic~Definitions:}}\)
- natural selection: evolutionary change due to differentiated survival and reproduction rates within a population
- relative fitness: an individual's likelihood to survive long enough and pass on their genes
- adaptation: trait that increases an organism's relative fitness
- polymorphism: multiple phenotypes in a species

\({\bf{Selection~Patterns:}}\)
- directional: increased distribution of trait towards one direction, changing the average value
ex. brain size relative to mass, increases up to a certain point in humanoid species
- stabilizing: selection against the extremes, decreases/maintains genetic polymorphism
ex. height, very small individuals in a species can be overpowered by larger ones, but being large requires more resources to maintain, thus imposing a selective pressure against the very large and very small
- disruptive: selection against the mean, increases genetic polymorphism
ex. if an enviornment has very light and very dark regions, then organisms that are very light or very dark will be able to blend in better, while organisms in the middle won't be able to blend in with either part of the enviornment

\({\bf{Other~Types~of~Selection:}}\)
- kin selection: in social organisms, altruistic organisms that sacrifice their own reproductive success by contributing to the success of other family members
- group selection: in social organisms, groups of altruistic organisms contribute to the survival of genes within their group, thus creating a selective pressure that favors altruism
- sexual selection: natural selection based entirely on reproductive success; competition for mates is key
> may result in sexual dimorphism, where selective pressures result in different phenotypes between sexes
> may result in traits that are disadvantageous to the individual but beneficial for reproductive success

Answer 2

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT