Agents of Evolutionary Change

Study Notes

There are five agents of evolutionary change: mutation, genetic drift, gene flow, non-random mating, and natural selection.

A mutation is a change to the nucleotide sequence in an organism's genetic material that occurs due to errors in DNA replication, exposure to UV or radiation, mutagens, and/or viruses.
Mutations create variation in gene pools and can be either favorable or unfavorable depending on the type of mutation and the environment.
Most mutations are minor and do not impact an organism's fitness, and many are repaired by cells before they become permanent.
Mutations provide new traits for natural selection to act upon.

The peppered moth evolved in response to pollution during the Industrial Revolution in England, resulting in a shift from light-colored to dark-colored moths.
As environmental standards improved, light-colored moths became common again, but the genetic change remained.

Natural selection is the process by which environmentally favorable genetic traits become more common in a population, while unfavorable traits become less common.
It acts on the observable characteristics of an organism, favoring those with advantageous traits.
Organisms with favorable traits are more likely to survive and reproduce, passing on those traits to their offspring.

Genetic drift is the random variation in which organisms reproduce, leading to changes in a population's genetic makeup over time.
It depends on a small population size, which increases the chance for change to occur permanently.
In larger populations, there is a normalizing effect that counteracts genetic drift.

Imagine a population represented by a jar of marbles, where the colors correspond to different gene outcomes.
Randomly selecting and replacing marbles represents the random reproduction of organisms.
Over time, the marble population may change due to chance, resulting in the loss of one color (gene outcome).

The finches discovered by Darwin on the Galapagos archipelago are an example of natural selection.
Each finch species has a beak adapted to its specific food source, resulting from genetic variations and environmental selection.

Gene flow is the movement of genes from one population to another, increasing genetic variation in the receiving population.
It can occur within a population, introducing new genes, or across populations, making them genetically similar and reducing speciation.

Non-random mating is the selection of mates based on specific traits, not by chance.
It occurs in humans, where people select mates based on appearance, cultural values, social rules, stature, or personality.
Non-random mating works against natural selection, as it is not only the environment selecting for certain traits.