Natural Selection and Evolutionary Mechanisms

Natural Selection

A mechanism for evolution that explains how adaptations arise and how species evolve over time.

Descent with Modification

The process by which species evolve over time, leading to adaptations and diversity of life.

Homologous Structures

Structures 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 ancestry.

Adaptations

Heritable characteristics that enhance an organism's ability to survive and reproduce in specific environments.

Variation

Differences in traits among individuals in a population.

Reproductive Success

The ability of an individual to produce offspring that survive to reproductive age.

Heritability

The ability of traits to be passed from parents to offspring.

Differential Reproductive Success

The concept that individuals with traits better suited to the environment are more likely to survive and reproduce.

Fitness

A reference to the reproductive success of an individual in a population.

Evolution

A change in the genetic makeup of a population over time.

Charles Lyell

An English geologist who proposed that geological processes have been uniform over a long period, suggesting an old Earth.

Jean-Baptiste de Lamarck

A scientist who proposed a flawed mechanism for evolution based on the inheritance of acquired characteristics.

Use and Disuse

Lamarck's idea that body parts used extensively become larger and stronger, while those not used deteriorate.

Inheritance of Acquired Characteristics

Lamarck's assumption that traits acquired during an organism's lifetime could be passed to the next generation.

Charles Darwin

The scientist whose voyage on the HMS Beagle led to the development of the theory of evolution by natural selection.

Fossils

Remains of ancient organisms that provide evidence of changing life forms over time.

Genetic Variations

Differences in DNA among individuals that can be selected for or against in different environments.

Environmental Change

A change in the surroundings that can lead to adaptation of populations through natural selection.

Population Evolution

The process by which the genetic makeup of a population changes over time due to natural selection.

Old Earth

The concept that the Earth is much older than a few thousand years, allowing time for evolution.

Artificial selection

The process by which species are modified by humans. Example: Selective breeding for milk or meat production; development of dog breeds.

Direct observations

Direct observations of evolutionary change provide evidence for the theory of evolution. Populations of organisms continue to evolve in real time.

Homology

Characteristics in related species can have an underlying similarity even though they have very different functions. Similarity resulting from common ancestry is known as homology.

Fossil record

Fossils are remains or traces of organisms from the past. They are found in sedimentary rock and show that evolutionary changes have occurred over time.

Biogeography

The geographic distribution of species provides evidence for the theory of evolution. Species in a discrete geographic area tend to be more closely related to each other than to species in distant geographic areas.

Vestigial organs

Structures of marginal, if any, importance to the organism. They are remnants of structures that served important functions in the organisms' ancestors.

Molecular homologies

Shared characteristics on the molecular level. Example: All life forms use the same genetic language of DNA and RNA.

Homologous structures

Anatomical signs of evolution. Examples: Forelimbs of mammals that are now used for a variety of purposes, such as flying in bats or swimming in whales.

Convergent evolution

Occurs when two species develop similarities as they adapted to similar environmental challenges, not because they evolved from a common ancestor.

Analogous structures

Similar solutions to similar problems that do not indicate close relatedness. Example: Bird wing and butterfly wing.

Transitional fossils

Fossils that link ancient organisms to modern species, providing evidence of evolutionary changes as predicted by Darwin's theory.

Paleontology

The study of fossils.

Bacterial resistance

Bacterial populations become resistant to antibiotics, providing evidence for evolutionary change.

Embryonic homologies

Comparison of early stages of animal development reveals many anatomical homologies in embryos that are not visible in adult organisms.

Common ancestor

An ancestor from which two or more species have evolved.

Selection

The process by which certain traits become more common in a population due to the increased likelihood of survival and reproduction.

Evolution

The process through which species change over time through mechanisms such as natural selection and genetic drift.

Survival of the fittest

A phrase often misused; instead, describe how selection favors a feature that results in leaving more offspring.

Species

A group of organisms that can interbreed and produce fertile offspring.

Niche

The role or function of an organism or species within an ecosystem.

Genetic language

The universal code of DNA and RNA used by all life forms.

Environmental challenges

Conditions that require organisms to adapt in order to survive and reproduce.

Anatomical homologies

Similar structures in different species that indicate a common ancestry.

Selective breeding

The process of breeding plants and animals for particular genetic traits.

Continental drift

The movement of the Earth's continents relative to each other, explaining the similarity of species on distant continents.

Endemic species

Species that are found at a certain geographic location and nowhere else.

Evolution

Change in the genetic makeup of a population over time.

Overproduction of offspring

A phenomenon where more offspring are produced than can survive, leading to competition for resources.

Heritable variations

Differences within a population that can be passed from parents to offspring.

Differential reproductive success

The concept that some individuals in a population are more successful at reproducing than others due to variations.

Natural selection

The process by which certain traits become more common in a population due to their advantages in survival and reproduction.

Mutations

Changes in the DNA sequence that are the only source of new genes.

Hardy-Weinberg equilibrium

A condition in which allele frequencies in a population remain constant over time in the absence of evolutionary influences.

Hardy-Weinberg equation

A mathematical formula used to calculate allele frequencies in a population to test whether it is evolving.

Genetic drift

Random changes in allele frequencies in a population, often having a more significant effect in small populations.

Migration

The movement of individuals into or out of a population, affecting allele frequencies.

Phenotypic variation

Observable differences in the traits of individuals, often reflecting genetic variation.

Point mutations

Changes in a single nucleotide base in a gene that can significantly impact phenotype.

Chromosomal mutations

Mutations that delete, disrupt, duplicate, or rearrange many loci at once, often harmful but not always.

Gene duplications

The process where mistakes in crossing over result in an expanded genome with new genes.

Sexual reproduction

The process that shuffles existing alleles and produces individual genotypes through random assortment.

Population

A group of individuals of the same species that live in the same area and interbreed.

Population genetics

The study of how populations change genetically over time.

Gene pool

All of the alleles at all loci in all members of a population.

Five Conditions for Hardy-Weinberg Equilibrium

1. No change in allelic frequency due to mutation 2. Random mating 3. No natural selection 4. Extremely large population size (no genetic drift) 5. No migration.

Hardy-Weinberg equilibrium

The frequencies of alleles and genes in a population's gene pool will remain constant over the course of generations unless acted upon by forces other than Mendelian segregation and the recombination of alleles.

Evolution

A change in allelic frequencies.

Hardy-Weinberg equation

p² + 2pq + q² = 1, which indicates the frequencies of the three genotypes.

p

The frequency of the dominant allele.

q

The frequency of the recessive allele.

p²

Frequency of AA (homozygous dominant).

2pq

Frequency of Aa (heterozygous).

q²

Frequency of aa (homozygous recessive).

p + q

Equals 1, representing the total frequency of alleles for a gene.

Dominant phenotype

Includes both p² and 2pq.

Square root of q²

Used to find q, the frequency of the recessive allele.

Natural selection, genetic drift, and gene flow

Forces that can alter allele frequencies in a population.

Null hypothesis in Hardy-Weinberg analysis

If Hardy-Weinberg analysis shows a change in allelic frequency, you can ask which of the five conditions is not being met.

allelic frequencies

The relative frequency of an allele at a genetic locus in a population, expressed as a proportion or percentage.

mutations

Changes in the DNA sequence that can alter gene frequency, though they are typically rare and result in small changes across generations.

natural selection

The process whereby organisms better adapted to their environment tend to survive and produce more offspring, leading to a change in allelic frequencies.

differential reproductive success

The concept that individuals with variations better suited to their environment tend to survive and reproduce more than those less suited.

adaptive evolution

Evolution that results in organisms becoming better suited to their environment, primarily driven by natural selection.

genetic drift

The unpredictable fluctuation in allele frequencies from one generation to the next, more pronounced in smaller populations.

loss of genetic diversity

A reduction in the variety of genes in a population, which can occur due to genetic drift.

Founder effect

A phenomenon where a small group of individuals becomes isolated from a larger population, leading to a new population with a gene pool that differs from the source population.

Bottleneck effect

A sharp reduction in population size due to environmental events, resulting in a gene pool that may not reflect the original population's genetic diversity.

gene flow

The transfer of alleles or genes from one population to another, often through migration, which can reduce genetic differences between populations.

relative fitness

The contribution an organism makes to the gene pool of the next generation relative to the contributions of other members.

fitness in evolution

Measured solely by reproductive success, not by the strength or size of an organism.

phenotype

The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences.

genotype

The genetic constitution of an individual organism.

directional selection

A mode of natural selection that favors one extreme phenotype over the mean or other extreme, shifting the overall makeup of the population.

disruptive selection

A mode of natural selection that favors extreme phenotypes at both ends of the distribution, leading to a disadvantage for intermediate phenotypes.

selective pressures

Environmental factors that influence which individuals in a population survive and reproduce.

patchy habitat

An environment that consists of distinct areas with different characteristics, which can influence the survival and reproduction of organisms.

Stabilizing selection

Removes extreme variants from the population and preserves intermediate types.

Directional selection

Example: Large black bears survived periods of extreme cold better than smaller ones and so became more common during glacial periods.

Disruptive selection

Example: A population has individuals with either large beaks or small beaks but few with the intermediate-sized beaks.