Unit 7 - Natural Selection and Evolution

It covers key concepts in evolutionary biology, starting with mechanisms of evolution and selection such as natural selection, sexual selection (including intrasexual, intersexual, the handicap principle, and the good genes hypothesis), as well as directional, disruptive, stabilizing, and frequency-dependent selection. Additionally, it explores population genetics topics like genetic drift, the founder effect, the bottleneck effect, gene flow, allele frequencies, inbreeding, and Hardy-Weinberg Equilibrium. The set also examines speciation and isolation mechanisms—including allopatric and sympatric speciation, polyploidy, adaptive radiation, prezygotic and postzygotic barriers, and hybrid zone dynamics. Finally, it details evidence for evolution through fossil records, homologous, analogous, and vestigial structures, embryology, biogeography, and molecular biology, along with statistical tools like Chi-Square analysis, null hypotheses, and P-values.

Evolution

The change in a population over generations at a genetic level, which we can see as a change in phenotypes over time.

Adaptation

A trait that increases the probability of successful reproduction in a specific environment.

Natural Selection

The mechanism for evolving adaptations where individuals with traits that increase their likelihood of survival and reproduction leave more offspring.

Microevolution

The change in the genetic structure of a population from one generation to another, reflected in phenotypic changes.

Macroevolution

Large scale change in species over paleontological time, such as the appearance of new species.

Allopatric Speciation

Speciation that occurs due to geographic separation of populations from a parent species.

Sympatric Speciation

Speciation occurring within a parent species that remains in one location.

Polyploidy

The unequal division of chromosomes during meiosis, which can lead to speciation.

Autopolyploidy

When all the of the chromosomes move into one new cell instead of separating due to an error in meiosis

Allopolyploid

When gametes from two different species combine (notice how it takes two generations, or two reproductive acts, before the viable fertile hybrid results)

Intrasexual Selection

Competition among males for access to females that can lead to the development of certain traits.

Intersexual Selection

Females choose males based on certain desired characteristics.

Divergent Evolution

When two species evolve in diverse directions from a common point.

Convergent Evolution

When similar traits evolve independently in two species that do not share a recent common ancestry.

Genetic Variation

Differences in DNA sequences within a population that contribute to phenotypic variation.

Dispersal Group

When a few members of a species move to a new geographical area

Vicariance Group

When a natural situation arises to physically divide organisms

Adaptive Radiation

Where many adaptations evolve from a single point of origin; thus, causing the species to radiate into several new ones

Reproductive Isolation

The ability to interbreed

Prezygotic barrier

A mechanism that blocks reproduction from taking place

Postzygotic barrier

Occurs after zygote formation

Temporal isolation

A form of reproductive isolation (differences in breeding schedules)

Habitat isolation

When populations of a species move to a new place that no longer overlaps with the same species' other populations

Behavioral isolation

When the presence or absence of a specific behavior prevents reproduction

Gametic barrier

When differences in a species gamete cells (eggs and sperm) prevent fertilization from taking place

Hybrid inviability

When hybrid individuals cannot form normally in the womb and simply do not survive past the embryonic stages

Hybrid sterility

When reproduction leads to hybrid birth that is sterile

Hybrid Zone

An area where two closely related species continue to interact and reproduce, forming hybrids.

Changes in Hybrid Zone: Reinforcement

Hybrids are less fit than either purebred species. The species continue to diverge until hybridization can no longer occur.

Changes in Hybrid Zone: Fusion

Reproductive barriers weaken until the two species become one.

Changes in Hybrid Zone: Stability

Fit hybrids continue to be produced.

Gradual Speciation Model

Where species diverge gradually over time in small steps

Punctuated Equilibrium Model

Where a new species undergoes changes quickly form the parent species, and then remains largely unchanged for long periods of time afterwards

Chi-Square Analysis

A statistical method used to determine if there is a significant difference between observed and expected frequencies in categorical data.

Null Hypothesis ($H_0$)

The hypothesis that there is no difference between the two different groupings, with any difference due to chance alone.

P-value

A statistic that describes the probability of observing the data under the null hypothesis.

Evidence of Evolution: Fossils

Show the gradual evolutionary changes over time (over millions of years)

Evidence of Evolution: Anatomy

Allows us to see the similarities between different species' bone structures to trace evolution through change in bone structure and function, revealing common ancestry.

Evidence for Evolution: Embryology

Studying the development of embryos across different species reveals similarities that suggest common ancestry and evolutionary relationships.

Evidence for Evolution: Biogeography

Examines the geographic distribution of species and how it reflects evolutionary history, showing how related species are often found in close geographical proximity.

Evidence for Evolution: Molecular Biology

Analyzing DNA, RNA, and protein similarities among different organisms provides insight into evolutionary relationships and common ancestry, highlighting genetic similarities and variations.

Vestigial Structures

Unused structures in an organism that have lost their original function through evolution.

Homologous Structures

Anatomical features that are similar in different species due to shared ancestry.

Analogous Structures

Structures that serve similar functions in different species but do not share a common ancestor.

Species

A group of actual or potential interbreeding individuals that can produce fertile offspring.

Genetic Drift

Random changes in allele frequencies in a population, which can lead to evolutionary change (random, not selective, not adaptive)

Founder Effect

New population is founded by a small group previously part of a larger population

Bottleneck Effect

The occurrence of a catastrophic event that results in a major decline in population size, leading to a reduction in genetic diversity and potential loss of alleles

Directional Selection

A mode of natural selection where one extreme phenotype is favored over others, causing allele frequencies to shift over time in that direction.

Disruptive Selection

A mode of natural selection that favors extreme phenotypes at both ends of the spectrum over intermediate phenotypes, leading to increased genetic diversity.

Stabilizing Selection

A mode of natural selection that favors intermediate phenotypes over extremes (due to competing selective pressures), reducing variation and maintaining the status quo in a population.

Population

A group of organisms of the same species that live in a particular area and interbreed, sharing a common gene pool.

Gene Pool

A collection of all alleles in a population

Allele Frequency

The proportion of a specific allele among all alleles for a particular gene in a given population.

Hardy-Weinberg Equilibrium

A framework for determining if populations are evolving (the null hypothesis for selection)

Restrictions for Hardy-Weinberg Equilibrium

The species is diploid and sexual, population is large, no migration, mating is random, no mutation (all the conditions must be met at once)

Allele Frequency (Gene Frequency)

The rate at which a specific allele appears within a population

Heritability

The proportion of total phenotypic variation in a trait that is attributable to genetic variation among individuals in a population.

Inbreeding

The mating of closely related individuals that can lead to a reduced genetic diversity and increased chances of genetic disorders.

Inbreeding Depression

A reduction in biological fitness in a given population due to inbreeding, which increases the likelihood of homozygosity for deleterious alleles.

Gene Flow

The transfer of genetic material between populations through migration of individuals or gametes, which can increase genetic diversity.

Fecundity

The ability to reproduce

Frequency-Dependent Selection

Favors phenotypes that are common or rare

Sexual Dimorphisms

Physical differences between sexes in a species, often associated with mating behaviors or reproductive strategies.

Handicap Principle

A theory suggesting that exaggerated traits in males are costly to maintain, serving as honest signals of fitness to potential mates.

Good Genes Hypothesis

Males develop these impressive ornaments to show off their efficient metabolism or their ability to fight disease