23.4 Natural Selection is the only mechanism that consistently causes adaptive evolution

Intersexual selection-

-Individuals of one sex (usually females) are choosy in selecting their mates from the other sex. -Peacock females choose males that have the brightest and largest plumage. -While this bright plumage may leave the male more vulnerable to predation, the new reproductive success outweighs that risk. -Also, the traits females choose for tend to be indicative of good genes, which means that they tend to choose the males that have better genes that are more fit for survival than others

Why can't Natural selection fashion perfect organisms

-Selection can act only on existing variations -Evolution is limited by historical constraints -Adaptations are often compromises -Chance, natural selection, and the environment interact -The environment is constantly changing

Directional Selection-

-occurs when conditions favor individuals exhibiting one extreme of a phenotypic range -This shifts the population's frequency curve for the phenotypic character in one direction or the other Ex. Large seeds became more common, large beaks more effective, directional selection in the direction of large beaks

Sexual Dimorphism-

A difference between the two sexes in secondary sexual characteristics Ex. Size, color, ornamentation, and behavior

Sexual Selection-

A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates

Stabilizing selection-

Acts against both extremes and favors intermediate variants Ex. Human babies have a birth weight usually between 3-4 kg. If they are much bigger or smaller, they can suffer higher rates of mortality

Fitness-

Describes how well an organism can survive and reproduce in its environment.

Evolution is limited by historical constraints

Evolution has to work around the existing structure given by the past ancestors. You can't ever start completely from scratch in evolution.

Example of relative fitness

Ex. A moth may happen to have more offspring because it's body coloring can conceal it from predators better

Adaptations are often compromises

Ex. Humans have sacrificed structural reinforcement of our limbs for agility. We can move fast be we are prone to injury

Example of Heterozygote Advantage

Ex. Occurs at the locus for a subunit of hemoglobin in humans -Homozygous recessive individuals have a recessive allele that causes sickle cell disease -Heterozygous individuals are protected from the most severe effects of malaria -The body kills sickle cells rapidly, along with the parasites they carry -Homozygous dominant people are still more vulnerable to the harmful effects of malaria

Example of FDS

Ex. Scale eating fish are either right mouthed or left mouth Right mouthed fish attack the left flank -Left mouthed fish attack the right flank -The prey defend the side getting attacked the most. -Natural selection favors the least common trait because is their were less lift mouthed, they would get more food than the right mouthed fish. -The frequency of each phenotype, even though right is dominant, is 50% each

Phenotypic polymorphism-

If two or more distinct morphs are each represented in high enough frequencies to be readily noticeable.

Frequency-dependent selection-

In this selection, the fitness of the phenotype depends on how common it is in the population

Selection can act only on existing variations

Natural selection only favors the fittest phenotypes, which may not be the most ideal traits. New alleles don't come out of nowhere right when they are needed.

Relative Fitness-

The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population.

Heterozygote Advantage-

When individuals who are heterozygous at a particular locus have greater fitness than both kinds of homozygotes -Two alleles maintained -Advantage defined in terms of genotype, not phenotype

Morphs-

an individual of one particular form, as a worker ant, in a species that occurs in two or more forms.

Disruptive selection-

occurs when conditions favor both extremes Ex. Large seeds and small seeds are common, large beaks and small beaks both survive better while intermediate dies out

Balanced polymorphism-

situation in which two different versions of a gene are maintained in a population of organisms because individuals carrying both versions are better able to survive than those who have two copies of either version alone.

These factors limit the

success of natural selection

Genetic Polymorphism-

the occurrence together in the same population of two or more genetically determined phenotypes in such proportions that the rarest of them cannot be maintained merely by recurrent mutation.

The preservation of genetic variation Neutral Variation

- Differences in the DNA sequence that do not confer a selective advantage or disadvantage

Intrasexual selection-

- Selection within the same sex. Individuals of one sex compete directly for mates -Ex. A single male may fight for and patrol a group of females, preventing other weaker males from mating with them -Can be seen in males and/or females in certain species

How does Diploidy preserve genetic variation

-Diploid eukaryotes have a large amount of genetic information in the form of hidden reccessive alleles -These recessive alleles can only be exposed to selection one both parents give in to a zygote, which is rare. -Heterozygote protection maintains a huge pool of alleles that may be used in the future to adapt to different conditions

Chance, natural selection, and the environment interact

Chance may not choose those with the alleles best suited for the environment The environment is constantly changing

Balancing Selection-

Occurs when natural selection maintains two or more forms in a population