A fifth factor, nonrandom mating, will disrupt the equilibrium but only by shifting frequencies.
People are more likely to mate with other people than with random people.
Nonrandom mating doesn't cause evolution directly.
Natural selection has been described.
Each generation, the allele's frequencies are changed by a small but continuous amount.
If no other forces act on the allele, it will slowly increase its frequencies in a population.
The population will be removed from the population at a low rate if natural selection acts against the allele.
The human population has genetic diseases that are very low in frequencies.
The allele will increase in frequencies if it is favored by selection.
Random changes in frequencies are caused by genetic drift.
In the next section, genetics can be important in evolution.
Frequency changes in both populations will be caused by the migration of individuals between them.
Populations are always evolving and the Hardy-Weinberg equilibrium will never be exactly observed because there is no population in which one or more of these processes are not operating.
Scientists can compare evolving populations and infer what evolutionary forces might be at play if they have a baseline expectation for allele frequencies in a non-evolving population.
The population is evolving if the frequencies of alleles are different from the values expected.
Sexual selection was identified by Darwin as a special case of natural selection.
Sexual selection affects an individual's ability to mate and thus produce offspring, and it leads to the evolution of dramatic traits that often appear maladaptive in terms of survival but persist because they give their owners greater reproductive success.
Male-male competition for mates and female selection of mates are two ways in which sexual selection occurs.
Conflicts between males can be ritualized, but they can also pose significant threats to a male's survival.
Females are more likely to mate with males with higher quality territories.
Female choice occurs when females choose a male based on a particular trait, such as feather colors, the performance of a mating dance, or the building of an elaborate structure.
The fighting ability, feather color, and length of the males become enhanced in each of these cases.
Sexual selection can lead to natural selection against a character's further enhancement preventing its further evolution because it negatively impacts the male's ability to survive.
An elaborate display or colorful feathers can make a male more obvious to a predator.
By the end of this section, you will be able to describe the four basic causes of evolution.
Natural selection, genetic drift, and migration are some of the factors.
We know they affect populations.
Natural selection has been discussed.
All genes are expressed in a specific way.
The individual with the phenotype has an advantage or disadvantage over the other individuals in the population.
If it is an advantage, that individual will have more offspring than individuals with the other phenotypes, and this will mean that the allele behind the phenotype will have greater representation in the next generation.
The offspring of those who are carrying the same allele will benefit if conditions remain the same.
The allele will increase in frequencies over time.
There are new all genes in a population.
There is a change in the sequence of the genes.
The net effect is a change in frequencies.
The effect on evolution is small unless it interacts with one of the other factors, such as selection.
There is a chance that the allele will be selected against, selected for, or neutral.
The process of evolution and its processes from the population will be found in very low frequencies.
The initial spread of beneficial mutations is slow.
Whether or not a genetic change is beneficial or harmful depends on whether the change helps the organisms survive to sexual maturity and reproduce.
It should be noted that the ultimate source of genetic variation in all populations are new alleles.
Genetic drift is the effect of chance and can change a population's frequencies.
Small populations have the most important genetic drift.
In a population with infinite individuals, no population is this large.
The alleles in an offspring generation are a random sample of the alleles in the parent generation.
It is possible that alleles will not make it into the next generation due to chance events such as mortality of an individual, events affecting finding a mate, and even the events affecting which gametes end up in fertilizations.
A tenth of the population's genes will be lost if one individual dies before any offspring are born.
In a population of 100, only 1 individual has a significant impact on the population's genetic structure and it is unlikely to remove all copies of a rare allele.
The next generation will have ten people.
It is not likely that the next generation will have the same number of alleles.
There are at least six of one and four of the other frequencies.
The frequencies of the alleles have changed.
The odds are that a coin won't work to choose the next generation.
It could take a long time for a large population.
It can be shown that real populations behave this way.
The effect of drift on frequencies is greater for smaller populations.
The effect is more pronounced on an allele with a far from one half Frequency.
Even those that are naturally selected will be influenced by drift.
Genetic drift in a population can lead to the elimination of an allele.
The next generation is produced by a random group of individuals.
The frequencies of alleles in the next generation are the same as they are in the individuals reproducing.
The genetic structure of the survivors becomes the genetic structure of the entire This OpenStax book, which may be very different from the pre-disaster population.
Disasters that kill for other reasons, such as a hurricanes or lava flow, are not related to the organisms' characteristics.
A mass killing caused by cold temperatures at night is likely to affect individuals differently depending on their alleles.
The genetic variability within a population can be reduced by a chance event.
If a portion of the population leaves to start a new population in a new location, or if a population gets divided by a physical barrier, it could be a scenario in which genetic drift is strong.
The founder effect occurs when the genetics of the new population match those of the founding fathers and mothers.
The founder effect is believed to be a key factor in the genetics of the Afrikaner population of Dutch settlers in South Africa.
The founding colonists, who were a small sample of the original population, carried these changes.
You can learn more about genetic drift and run simulations of allele changes caused by drift.
Some populations are stable.
Many plants send their seeds far and wide, by wind or in the guts of animals, which can introduce rare alleles to a new population in which they are rare.