19.3 Adaptive Evolution

The result can be a changing population if individuals don't randomly mate with each other.

Simple mate choice is one reason.
Peahens may prefer peacocks with bigger tails.

Natural selection picks characteristics that lead to more sexual selections for an individual.

Physical location is a cause of nonrandom mating.

In large populations spread over vast geographic distances, not all individuals will have equal access to one another.
Some might be miles apart through the woods or over rough terrain.

Population variation can be determined by more than just genes.

A city dweller is more likely to have darker skin than a beachgoer due to regular exposure to the sun.
Some species have major characteristics determined by the environment.

Some turtles and other reptiles have sex determinations that are dependent on temperature.

If females are at a different temperature range than males, they will develop into males.

The American alligator's (Alligator mississippiensis) produce females and males when the eggs are at 30 and 33 degrees.

There can be differences in the variation between populations.

Smaller bodies in the cooler climates closer to the earth's poles allow species of warm-blooded animals to better conserve heat.

This is aitudinal line.

Depending on where they are along a mountain slope, flowering plants bloom at different times.
This is aitudinal line.

The individuals will show gradual differences in their phenotype if there is gene flow between the populations.

Alterations, even speciation, can be caused by restricted gene flow.

By the end of this section, you will be able to explain the different ways natural selection can shape populations.

If an individual carries an allele that results in a fatal childhood disease and also carries a beneficial genotype that increases the ability to reproduce, that fecundity phenotype will not pass to the next generation.

Individuals with greater contributions to the gene pool of the next generation are selected.

Scientists measure fitness in the field.

It isn't an individual's fitness that counts, but how it compares to the other organisms in the population.

Stabilizing selection is one of the ways that selection can affect population variation.

Individuals can become more or less genetically similar and the phenotypes can become more similar as a result of natural selection.

Natural selection is likely to favor mice that blend in with the forest floor and are less likely for predators to spot them.

If the ground is a shade of brown, the mice that have fur that is close to that color will be more likely to survive and reproduce.
The lighter the mice are, the more likely they are to fall victim to a predator.
The population's genetic variance will decrease as a result of this selection.

The evolution of the peppered moth in England in the 18th and 19th century is a classic example of this type of selection.

Prior to the Industrial Revolution, the moths were mostly light in color, which allowed them to blend in with the trees and lichens in their environment.
As soot began to come from factories, the trees darkened and the light-colored moths became easier to spot.
The moth's melanic form increased in frequencies because they had a higher survival rate in habitats that were affected by air pollution.
If something were to cause the forest floor to change color, the mouse population could evolve to take on a different color.
The result of this type of selection is a shift in the population's genetics.

Some things in science are true and new information can change our understanding.

Some scientists have questioned the facts behind the selection of the peppered moths.
You can read this article to learn more.

Sometimes two or more distinct phenotypes can each have their advantages for natural selection.

Large, dominant alpha males use brute force to obtain mates, while small males can sneak in for furtive copulations with the females in an alpha male's territory.
Medium-sized males who can't overtake the alpha males and are too big to sneak copulations are selected against the alpha males.
When environmental changes favor individuals on either end of the spectrum, diversifying selection can happen.
Imagine a mouse population living on a beach with sand and grass.
Light-colored mice that blend in with the sand would be favored, as well as dark-colored mice that can hide in the grass.
Medium-colored mice would not blend in with either the grass or the sand, and thus would most likely be eaten by a predator.
The population becomes more diverse as a result of this type of selection.

Natural selection can affect the distribution of phenotypes.

An average phenotype is favored in stabilizing selection.
The spectrum of observed phenotypes can be shifted by a change in the environment.
Two or more extreme phenotypes are selected for, while the average phenotype is not.

In the last few years, factories have become cleaner and less harmful to the environment.

An example of this type of selection can be seen in a group of Pacific Northwest lizards.

There are three throat-color patterns for male common side-blotched lizards.
The reproductive strategy of each form is that orange males are the strongest and can fight other males for access to their females.
Medium-sized blue males form strong bonds with their mates.

Yellow males look a bit like females, which allows them to sneak copulations.

Like a game of rock-paper-scissors, orange beats blue, blue beats yellow, and yellow beats orange in the competition for females.
The big orange males can fight off the blue males to mate with the blue's pair-bonded females, the blue males are successful at guarding their mates against yellow sneaker males, and the yellow males can sneak copulations from the potential mates of the large.

A yellow-throated side-blotched lizard is smaller than either the blue-throated or orange-throated males and appears a bit like the females of the species, allowing it to sneak copulations.

When blue males dominate the population, natural selection favors orange males.

When the population is mostly yellow males, blue males will thrive, while yellow males will be selected for when orange males are the most populous.
In one generation, orange might be the dominant color, and then yellow males will start to rise in frequencies.
Blue males will be selected when yellow males make up a majority of the population.
When blue males become common, orange males will once again be favored.

Positive and negative frequencies are used to increase the population's genetic variance by selecting for rare phenotypes.

The differences between males and females of certain species are not limited to the reproductive organs.

The peacock's tail is one of the elaborate colors and adornments displayed by males, while females tend to be smaller and duller in decoration.
Some males get the majority of the total matings, while others don't.
The males are better at fighting off other males or females will choose to mate with the bigger or more decorated males.
The evolution of bigger body size and elaborate ornaments to attract the females' attention is a result of the variation in reproductive success.
Females are more likely to select more desirable males if they achieve a few selected matings.

Some species have sex-role reversed.

In such cases, females tend to have a greater variation in their reproductive success than males and are usually selected for the larger body size and more elaborate characteristics of males.

In peacocks and peahens, the female spider is larger than the male one, and in wood ducks, the female spider is larger than the male one.

The selection pressures on males and females are what we call them.

Secondary sexual characteristics that do not benefit the individual's likelihood of survival can result in maximized reproductive success.

Sexual selection can be so strong that it can damage an individual's survival.

While it is beautiful and the male with the largest tail is more likely to win the female, it is not the most practical appendage.
It makes the males slower in their attempts to escape.
Females like the big tails because of the risk.
The larger the tail, the more fit the male is.

Females choose males with the most impressive features because it signals their genetic superiority, which they will pass on to their offspring.

One may argue that females should not be picky because it will reduce their number of offspring, but if better males father more fit offspring, it may be beneficial.
The chances of survival may be increased by fewer, healthier offspring.

Ronald Fisher proposed a model of sexual selection in 1915, which suggests that selection of certain traits is a result of sexual preference.

Natural selection can create populations that are better adapted to survive and reproduce in their environments.

Natural selection can't produce perfect organisms.
Natural selection is limited to existing variation in the population.
It doesn't create anything from scratch.
It is limited by a population's existing genetic variation and any new alleles that arise through gene flow.

Natural selection is limited because it works at the individual level and some alleles are linked due to their physical proximity in the genome, making them more likely to pass on together.

Some individuals may carry some beneficial and unfavorable alleles.
Natural selection can act upon the alleles' net effect.
Good alleles can be lost if people also have bad alleles.

Good alleles can be kept if they result in an overall fitness benefit.

Natural selection can be constrained by the relationships between different polymorphisms.

One morph may confer a higher fitness than another, but may not increase in frequency because going from the less beneficial to the more beneficial trait would require going through a less beneficial phenotype.
There are mice at the beach.
Some are light-colored and blend in with the sand, while others are dark and blend in with the grass.
The dark-colored mice may be more fit than the light-colored mice, and one might expect the light-colored mice to be selected for a darker color.
The medium-colored coat is bad for the mice because they can't blend in with the sand or grass.

Not all evolution is adaptive.

Natural selection often results in a more fit population, but other forces of evolution, including genetic drift and gene flow, often do the opposite.
Evolution isn't changing a population into an ideal.
It is the sum of the various forces that we have described in this chapter and how they affect the population's genetics.

Evolutionary theory grew out of the fact that both genetic and environmental factors can affect a population.

The more modern study of confer different phenotypes and different environments can population genetics.
The evolution causes individuals to act differently.
Only those populations and species from small-scale changes among differences in an individual's genes can individuals to large-scale changes over paleontological time pass to its offspring.
Scientists can selection to understand how organisms evolve.
Natural selection works by selecting alleles that track populations' frequencies over time.
Scientists can conclude that those for deleterious qualities are those who differ from each other.
The population is not in equilibrium with the genes, and this leads to genetic drift.

Gene flow can change frequencies when individuals leave or join the population.

New variation into a population may be caused by genetic changes.

Natural selection acts to increase the frequency of selection, in which individuals with positive beneficial alleles and traits while decreasing the frequency of frequency- dependent selection, or negative frequency deleterious qualities, is adaptive evolution.

The selection is natural dependent.
Sexual selection acts at the individual level, selecting for those that results from one sex having more variation in their fitness compared to the rest of the reproductive success than the other.
If the fit phenotypes are similar, females experience different pressures, which can natural selection result in stabilizing selection, and an often lead to the evolution of phenotypic differences, or overall decrease in the population's variation.

Microevolution describes the evolution of organisms that came from Europe.

The had polydactyly, a rare dominant trait, was one of the evolutions of the ship's captain.

Microevolution describes the evolution of organisms in the Amish population.

This is over their lifetimes, while macroevolution describes the evolution of organisms over multiple generations.

Natural selection offspring of two unrelated individuals are often not as good as offspring of closely related individuals.

Close relatives are not compatible.

People of one sex develop impressive offspring because their genes react negatively in the d.

An example of a trait that may have evolved as a flower is undergoing evolution.

bees seem to think that there is a result of the handicap principle.

Population blue flowers can be affected by evolution.

In a separate experiment, you discover variation and describe how they affect the color of the flower.