Evolution

What is Evolution?

The idea that living species are descendants of ancestral species that were different from present.

Adaptive Radiation

A process in which organisms diversify rapidly from an ancestral species into new forms, particularly when the environment changes.

Natural Selection

The process where individuals with advantageous traits survive and reproduce, passing those traits to the next generation.

Observation 1 of Darwin’s Argument

Members of a population often vary in their inherited traits (phenotypes).

Observation 2 of Darwin’s Argument

All species are capable of producing more offspring than the environment can support.

Inference 1 of Darwin’s Argument

Individuals with inherited traits that increase survival and reproduction leave more offspring.

Inference 2 of Darwin’s Argument

Unequal survival and reproduction leads to the accumulation of favorable traits in the population.

Adaptations

Inherited traits that increase an organism’s probability to survive and reproduce.

Fitness

The measurement of how well an organism can survive and reproduce in its environment.

Jean-Baptiste Lamarck's Hypothesis

Organisms have an innate desire to improve and can pass on traits acquired during their lifetime.

Individuals don’t adapt and evolve—who does?

Populations do.

Evidence of Evolution

Includes direct observation, selective breeding, fossil record, anatomical homologies, molecular homologies, and convergent evolution.

Direct Observation in Evolution

The evolution of antibiotic resistance, as seen in MRSA strains surviving exposure to methicillin.

Selective Breeding

The process where humans mimic evolution by breeding individuals with desired characteristics.

Fossil Record

Provides evidence of species extinction, origin, and changes within groups over time.

Homology

Similarity resulting from common ancestry.

Homologous Structures

Anatomical resemblances in different species that represent variations on a structural theme from a common ancestor.

Vestigial Structures

Remnants of features that served important functions in the ancestors of the organism.

Molecular Homologies

Genetic similarities shared among organisms inherited from a common ancestor.

Convergent Evolution

The evolution of similar traits in distantly related groups due to adaptation to similar environments.

Microevolution

The change in allele frequencies of a population’s gene pool over generations.

Speciation

The formation of a new species.

Macroevolution

Broader scale evolutionary changes that occur over a geological time scale.

Hardy-Weinberg Equilibrium

Condition in which allele frequencies remain constant over generations.

Five Conditions for Hardy-Weinberg Equilibrium

No mutation, random mating, no natural selection, extremely large population size, no gene flow.

Hardy-Weinberg Equation for Alleles

p + q = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele.

Hardy-Weinberg Equation for Genotypes

p² + 2pq + q² = 1, where p² is homozygous dominant, 2pq is heterozygous, and q² is homozygous recessive.

Directional Selection

Selection that favors one extreme phenotype over another.

Disruptive Selection

Selection that favors extreme phenotypes at both ends of the spectrum.

Stabilizing Selection

Selection that favors the intermediate phenotype over extremes.

Genetic Drift

Change in allele frequencies due to random chance, not selection.

Bottleneck Effect

A significant reduction in population size leading to reduced genetic variation.

Founder Effect

When a new population is established by a small number of individuals from a larger population.

Cladogram

A branching diagram representing a hypothesis about evolutionary history of a group of organisms.

Root of a Cladogram

The base of the tree representing the common ancestor for all organisms.

Outgroup

The group that is least related to the others in a cladogram.

Derived Character

A feature that distinguishes one group from another in evolutionary terms.

Node in a Cladogram

Point of divergence between lineages representing a common ancestor.

Genetic Variation

Variations in traits among individuals of a species.

Geographic Variation

Differences in populations found in different geographic areas.

Selection Pressures

Environmental factors that affect survival and reproduction of individuals.

Punctuated Equilibrium

Theory that evolution occurs in rapid bursts followed by long periods of little change.

Gradualism

Theory that species evolve through gradual, incremental changes.

Biological Species Concept

Defines a species based on reproductive compatibility; a group whose members can interbreed in nature.

Allopatric Speciation

Speciation that occurs due to geographic isolation.

Sympatric Speciation

Speciation that occurs in overlapping populations without geographic isolation.

Prezygotic Barriers

Prevent mating attempts or fertilization between different species.

Habitat Isolation

Species rarely encounter each other because they occupy different habitats.

Temporal Isolation

Species breed at different times, preventing them from mixing gametes.

Behavioral Isolation

Unique courtship rituals prevent species from mating.

Mechanical Isolation

Morphological differences prevent successful mating.

Gametic Isolation

Sperm and egg of different species fail to fuse.

Postzygotic Barriers

Prevent hybrid offspring from developing into viable adults.

Reduced Hybrid Viability

Hybrids fail to develop or reach maturity.

Reduced Hybrid Fertility

Hybrids are sterile and cannot reproduce.

Hybrid Breakdown

First generation hybrids may be fertile, but subsequent generations are inviable or sterile.

Polyploidy

Presence of extra sets of chromosomes leading to new species, common in plants.

Gene Flow

Transfer of alleles or genes from one population to another.

Immigration

The influx of new individuals into a population, which can increase genetic variation.

Emigration

The exit of individuals from a population, which can decrease genetic diversity.

Fitness in Evolution

The ability of an organism to survive and reproduce in its environment.

Ecosystem Changes and Natural Selection

Natural selection may enable populations to adapt to new environmental conditions.

Branching Tree of Life

Illustrates the evolutionary relationships between different species.

Survival of the Fittest

Phrase that summarizes the processes of natural selection.

Variation in Traits

Differences among individuals that can be acted upon by natural selection.

Environmental Changes as Drivers of Evolution

Changes can create new challenges leading to adaptation or extinction.

Inheritance and Evolution

Traits that are passed down from one generation to the next influence evolution.

Role of Mutation in Evolution

Mutations introduce genetic diversity, which is essential for evolution.