Evolution and the Origin of Species (Chapters 22-24)

Comprehensive vocabulary flashcards covering Darwinian evolution, evidence for descent with modification, population genetics, Hardy-Weinberg equilibrium, mechanisms of microevolution, reproductive isolation, and speciation dynamics from Chapters 22, 23, and 24.

Evolution

The process by which life has changed over time via descent with modification, defined genetically as a change in the genetic composition (allele frequency) of a population from generation to generation.

Natural Selection

A mechanism of evolution in which individuals that possess certain inherited traits tend to survive and reproduce at higher rates than individuals lacking those traits, driving adaptive change in populations.

Adaptation

Any inherited characteristic that enhances an organism's ability to survive and reproduce in a specific environment.

Mutation

A change in the nucleotide sequence of an organism's DNA, serving as the original raw material for all new genes and alleles; occurs spontaneously during DNA replication or via radiation and chemicals at a baseline rate of approximately 1 in every 100,000 genes per generation.

Extinction

The complete loss of a species, which naturally occurs when an organism's existing adaptations are no longer suited to an altered or shifting environment.

Scala Naturae

Aristotle's classical philosophical framework (also called the 'scale of nature' or 'great chain of being') that viewed species as permanent and unchanging, arranged in a fixed linear hierarchy from simple to complex.

Binomial Nomenclature

The two-part scientific naming system developed by Carolus Linnaeus that classifies organisms using their genus and specific epithet (for example, Homo sapiens).

Catastrophism

The historical geological principle championed by Georges Cuvier stating that sudden local natural catastrophes wiped out entire resident populations, with the area later being repopulated by species migrating from other locations.

Strata

Superimposed layers of sedimentary rock formed by successive deposits of compressed sediment, containing fossilized remains that preserve a chronological record of ancient life.

Inheritance of Acquired Characteristics

Jean-Baptiste de Lamarck's early, disproven evolutionary hypothesis proposing that traits developed or altered through use or disuse during an organism's lifetime (such as the stretching of a giraffe's neck) are directly passed down to offspring.

Artificial Selection

The selective breeding of domesticated animals and plants by humans over generations to isolate and propagate desired phenotypic traits.

Homology

Phenotypic or anatomical similarity between different organisms resulting from shared ancestry, such as the common arrangement of forelimb skeletal bones across humans, cats, whales, and bats.

Vestigial Structures

Remnants of historical anatomical features that served significant functions in an organism's evolutionary ancestors but are marginalized, useless, or nonfunctional in the modern organism (e.g., the human appendix and snake pelvis).

Convergent Evolution

The independent evolutionary development of analogous features in distantly related taxonomic lineages due to adaptation to similar environmental pressures rather than common descent.

Analogous Traits

Characteristics that share similar biological functions or superficial structures across species because of convergent evolution rather than common evolutionary ancestry.

Biogeography

The scientific discipline studying the spatial and temporal geographic distribution of biological species, historically influenced by continental drift and the breakup of Pangaea $250\text{ million}$ years ago.

Scientific Hypothesis

A testable and falsifiable explanation formulated for a specific, narrow set of biological observations or experimental questions.

Scientific Theory

A broadly framed, widely accepted explanation of natural phenomena that is substantiated by an extensive and repeatedly tested body of empirical evidence.

Microevolution

Evolutionary change on its smallest scale, defined as a change in allele frequencies in a population over successive generations, driven by natural selection, genetic drift, or gene flow.

Genetic Variation

Differences among individuals in their inherited DNA sequences or composition of genes, providing the necessary prerequisite upon which natural selection operates.

Discrete Characters

Heritable phenotypic traits that can be classified on an either-or basis with distinct categories and no intermediate states, such as purple versus white pea flowers or a hitchhiker's thumb.

Continuous Characters

Quantitative heritable traits that vary along a continuum within a population and are typically regulated by multiple genes, such as human height or skin color.

Allele

Any of the alternative versions of a specific gene that reside at the same chromosomal locus and can produce distinct phenotypic traits.

Locus

The specific, fixed physical position of a gene or allele along the length of a chromosome.

Genotype

The exact genetic composition or collection of alleles carried by an organism at one or more specific genetic loci.

Phenotype

The observable physical, physiological, and behavioral traits of an organism, produced by the interaction of its genotype with environmental factors.

Geographic Variation

Differences in the gene pools and allele frequencies between separate, geographically isolated populations of the same species.

Cline

A graded, continuous change in an inherited trait or allele frequency across a geographic or environmental axis, such as the cold-adaptive Ldh-B b allele frequency gradient in mummichog fish from Maine ($6^{\circ}\text{C}$) to Georgia ($21^{\circ}\text{C}$).

Hardy-Weinberg Equilibrium

A theoretical state in which allele and genotype frequencies in a non-evolving population remain strictly constant from generation to generation in the absence of evolutionary disturbing factors.

Hardy-Weinberg Assumptions

The five required conditions for a population to remain in genetic equilibrium: no mutations, random mating, no natural selection, extremely large population size (no genetic drift), and no gene flow.

Hardy-Weinberg Equations

The mathematical equations $p + q = 1$ (for allele frequencies) and $p^2 + 2pq + q^2 = 1$ (for genotype frequencies), where $p$ and $q$ represent the frequencies of two alternative alleles at a locus.

Genetic Drift

Unpredictable fluctuations in allele frequencies from one generation to the next caused entirely by chance events, producing pronounced evolutionary effects and allele loss in small populations.

Founder Effect

A form of genetic drift that occurs when a small group of individuals becomes isolated from a larger parent population to establish a new colony, resulting in a gene pool whose allele frequencies differ substantially by chance from the parent population.

Bottleneck Effect

A form of genetic drift resulting from a sudden, severe reduction in population size caused by an environmental disaster or human exploitation, leaving a surviving gene pool that randomly misrepresents the genetic diversity of the original population.

Gene Flow

The transfer of genetic alleles into or out of a population resulting from the movement and subsequent interbreeding of fertile individuals or the transport of their gametes.

Relative Fitness

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

Directional Selection

A mode of natural selection that shifts the overall phenotypic curve of a population by favoring individuals exhibiting one extreme of a phenotypic range over intermediate or opposing phenotypes.

Disruptive Selection

A mode of natural selection in which environmental conditions favor individuals displaying both phenotypic extremes over individuals with intermediate phenotypes.

Stabilizing Selection

A mode of natural selection that acts against both extremes of a phenotypic distribution, favoring intermediate variants and reducing phenotypic variation in a population.

Sexual Selection

A specialized form of natural selection in which individuals with certain inherited traits are more successful than others of the same sex at acquiring mates.

Sexual Dimorphism

Noticeable morphological and behavioral differences in secondary sexual characteristics between males and females of the same species, such as distinct coloration, ornamentation, or body size.

Intrasexual Selection

A type of sexual selection involving direct competition or combat among individuals of one sex (most frequently males) to secure access or mating rights to the opposite sex.

Intersexual Selection

A type of sexual selection (commonly termed mate choice) wherein individuals of one sex (usually females) actively select mates based on elaborate courtship displays, plumage, or morphological cues.

Speciation

The evolutionary lineage-splitting event by which one ancestral species diverges into two or more distinct descendant species, representing the focal origin of biodiversity.

Biological Species Concept

The definition of a species as a group of natural populations whose individual members possess the potential to interbreed and produce viable, fertile offspring, but cannot do so with members of other such groups.

Reproductive Isolation

The existence of biological barriers that impede individuals of two distinct species from interbreeding and producing viable, fertile progeny.

Hybrid

An offspring organism that results from an interspecific mating event between individuals belonging to two genetically distinct species (such as a zeedonk, liger, or tigon).

Prezygotic Barriers

Reproductive isolation mechanisms that impede mating attempts between species or prevent the completion of fertilization before a diploid zygote can be produced.

Habitat Isolation

A prezygotic barrier occurring when two species occupy different physical habitats within the same general geographic area and rarely or never encounter one another, even in the absence of physical barriers.

Temporal Isolation

A prezygotic barrier occurring when species breed during different times of the day, during different seasons, or in different years, preventing the mixing of gametes.

Behavioral Isolation

A prezygotic barrier driven by species-specific courtship rituals, vocalizations, or mating displays that fail to elicit recognition or acceptance from other species.

Mechanical Isolation

A prezygotic barrier caused by incompatible anatomical or morphological differences that physically prevent successful copulation or transfer of gametes, such as snails with oppositely spiraled shells.

Gametic Isolation

A prezygotic barrier where molecular incompatibility prevents the sperm of one species from fertilizing the eggs of another species, or sperm fails to survive within the female reproductive tract.

Postzygotic Barriers

Reproductive isolation mechanisms that act after fertilization has occurred to prevent hybrid zygotes from developing into viable, fertile reproductive adults.

Reduced Hybrid Viability

A postzygotic barrier where incompatible developmental genes from different parent species interact aberrantly, impairing hybrid embryonic development or survival to adulthood.

Reduced Hybrid Fertility

A postzygotic barrier where interspecific hybrids develop into robust adults but are sterile due to abnormal meiosis, preventing the production of functional gametes (e.g., the mule).

Hybrid Breakdown

A postzygotic barrier where first-generation ($F_1$) hybrids are viable and fertile, but when they mate together or backcross with a parent species, their offspring ($F_2$) are weak, defective, or sterile.

Allopatric Speciation

The emergence of new species that occurs when a parent population is subdivided into geographically isolated subpopulations that independently diverge genetically due to interrupted gene flow.

Sympatric Speciation

The formation of new species that occurs in populations inhabiting the exact same geographic region, facilitated by polyploidy, sexual selection, or habitat differentiation.

Polyploidy

A chromosomal mutation occurring during cell division that results in an organism possessing extra complete sets of chromosomes, commonly driving instantaneous sympatric speciation in plants.

Habitat Differentiation

A mechanism of sympatric speciation wherein a subpopulation exploits an ecological niche, host plant, or resource not utilized by the parental population (e.g., apple maggot flies switching from hawthorn trees to apple trees).

Hybrid Zone

A geographic area or contact boundary where individuals of closely related, genetically divergent species meet and mate, producing at least some offspring of mixed genetic ancestry.

Reinforcement

An evolutionary outcome in a hybrid zone where natural selection strengthens prezygotic reproductive barriers over time because hybrid offspring have lower fitness than parent species, progressively diminishing hybridization rates.

Fusion

An evolutionary outcome in a hybrid zone where reproductive barriers weaken and substantial gene flow occurs between species, causing the gene pools of the two parent species to merge into a single species.

Stability

An evolutionary outcome in a hybrid zone characterized by the continued, persistent production of hybrid individuals because hybrids survive or reproduce better than parent species in specific habitats or environmental periods.

Punctuated Equilibrium

A model describing the tempo of speciation wherein new species undergo rapid morphological change when first budding from a parent lineage, followed by prolonged periods of morphological stasis.

Gradualism

A model describing the tempo of speciation wherein species evolve and diverge continuously, slowly, and steadily from ancestral lineages over extended geologic time.

Macroevolution

Broad patterns of evolutionary change above the species level, representing the cumulative, long-term impact of numerous individual speciation and extinction events across geologic time.