5 Causes of Microevolution

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5 Processes That Cause Microevolution

Microevolution is caused by changes in DNA
A magnified portion of DNA. Getty/Steven Hunt

Microevolution is how individual traits within a population change over time. Remember that the Hardy Weinberg Principle says that in order for a population to change, some things must be assumed to be true. In other words, there must be some sort of process happening that causes microevolution. The five ways alleles within a population change over time are natural selection, migration, mating, mutations, or genetic drift.

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Natural Selection

There are three types of natural selection
Three types of natural selection. Getty/Encyclopaedia Britannica/UIG

Of course, natural selection is the main mechanism for microevolution. Alleles that produce favorable adaptations are more likely to be passed down to future generations because they allow those individuals to live long enough to reproduce. As a result, unfavorable adaptations are eventually bred out of the population and those alleles are removed from the gene pool. Over time, changes in allele frequency become more apparent when compared to previous generations. 

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Birds that migrate can change up their gene pool
Migrating birds. Getty/Ben Cranke

 Migration is the movement of individuals into or out of a population. Just like the migration of birds from the north to the south in the winter, organisms will sometimes change their locations and therefore change the gene pool of that population. If a new individual moves into a population, that is called immigration. If an individual moves out of a population, that is called emigration. Immigration causes different alleles to be introduced into the population and those are now available to be passed down via breeding with other members of the population. Emigration results in the loss of alleles from a population, which in turn would decrease the available genes in the gene pool.

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Mating Choices

Great Blue Herons have a mating ritual
Great Blue Herons. Getty/Coop's Captures Photography

Many species are not selective when it comes to mating. Asexual reproduction essentially clones the parent by copying its alleles without any sort of mating between individuals. Some species that use sexual reproduction will choose any available individual that is available as a partner with no regard for which characteristics they show. This keeps the alleles that are being passed down from generation to generation random.

However, many animal species are selective when finding a mate. These individuals look for particular traits in a mate that will translate to an advantage for their offspring. Since this mating is no longer random, many undesirable alleles are bred out of the population over several generations. This makes the gene pool shrink and fewer traits available for the next generation, causing microevolution.

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DNA mutations cause microevolution to happen
A DNA molecule with a mutation. Getty/Marciej Frolow

 Mutations change alleles by changing the actual DNA of the organism. There are several types of mutations that can occur and have varying degrees of change that accompany them. Alleles may not necessarily change if the change in DNA is small, like a point mutation, but could be lethal to organisms if it has a profound change, like a frame shift mutation. 0This change in DNA, if it occurs in the gametes can be passed down to the next generation. This either creates new alleles or removes existing traits from the population. However, cells are equipped with a system of checkpoints to make sure mutations do not occur and are corrected if they do. Mutations within populations that actually change the gene pool are rare.

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Genetic Drift

Founder Effect is a type of Genetic Drift
Genetic Drift (Founder Effect). Professor Marginalia

The smaller a population, the more likely it is to see significant microevolution related differences over generations. One of these changes that often happens randomly is called genetic drift. These changes are caused by the environment and other factors in every day life. The survival and reproduction of individuals could be affected and in turn change the frequency of some alleles seen in future generations of the population.

Genetic drift is not the same as mutations. While some environmental factors can mutate the DNA, genetic drift has more to do with behaviors, such as breeding times or geographic obstacles for smaller organisms.