Grade 12 Biology: Evolution and Mechanisms of Change

Comprehensive vocabulary flashcards covering evolutionary principles, mechanisms of selection, speciation, genetics, phylogenetics, and evidence for evolution based on Grade 12 Biology lecture notes.

Natural Selection

The non-random evolutionary process wherein environmental selective pressures act on existing heritable phenotypic variation, resulting in differential reproductive success where individuals with advantageous traits leave more surviving offspring.

Descent with Modification

The principle proposed by Charles Darwin that all species descend from ancestral species, spreading into different habitats over many eras and accumulating adaptations suited to each environment.

Fitness

A biological measure of an individual's relative ability to survive and reproduce in a specific environment, quantified directly by reproductive success rather than physical strength, size, or longevity.

VISTA

An acronym framing the key components of natural selection: Variation (trait differences exist in a population), Inheritance (variation is genetic and heritable), Selection (environmental pressures favour certain traits), Time (advantageous alleles become more common over generations), and Adaptation (the population becomes better suited to its environment).

Inheritance of Acquired Characteristics

Jean-Baptiste Lamarck's incorrect evolutionary hypothesis stating that modifications acquired by an individual during its lifetime through use and disuse (such as a giraffe stretching its neck) are passed on to its offspring.

Artificial Selection

A form of directional selection through controlled captive breeding practiced for over $10\,000$ years, in which humans intentionally choose and breed organisms possessing desired traits rather than allowing natural environmental pressures to govern reproductive success.

Heike Crab

A species of crab in Japan unintentionally selected by humans because fishermen threw back individuals whose carapaces resembled samurai faces, allowing those distinct shell patterns to increase in frequency.

Sexual Selection

A specific form of natural selection acting on traits that increase an individual's mating success, even when those traits impose survival costs or increase predation risk.

Sexual Dimorphism

Noticeable morphological, anatomical, or behavioral differences between males and females of the same species as a consequence of sexual selection.

Intersexual Selection

A type of sexual selection (mate choice) in which individuals of one sex (typically females) select mates based on elaborate physical displays, coloration, or vocalizations, such as peacock plumage.

Intrasexual Selection

A type of sexual selection involving direct competition or combat between members of the same sex (typically males) for access to mates, selecting for traits like larger body size, antlers, or defensive weaponry.

Directional Selection

A mode of natural selection that favours phenotypes at one extreme of a trait's distribution, causing the population's phenotypic curve to shift toward that extreme over time.

Stabilizing Selection

A mode of natural selection that favours intermediate phenotypes while selecting against both extremes, reducing phenotypic variation while maintaining the average trait value (e.g., human infant birth weight centered near $7\text{--}8\,\text{lbs}$).

Disruptive Selection

A mode of natural selection that selects against intermediate phenotypes and simultaneously favours individuals at both phenotypic extremes, producing a bimodal distribution that can potentially lead to speciation.

Biological Species Concept

The definition of a species as a group of interbreeding natural populations that can produce viable, fertile offspring with each other, but are reproductively isolated from other such groups.

Allopatric Speciation

Speciation that occurs when biological populations become geographically separated by a physical barrier (or colonization of an isolated area), preventing gene flow and allowing evolutionary divergence via mutation, selection, and drift.

Vicariance

An allopatric speciation mechanism in which an existing population is physically split into geographic isolates by the formation of a new natural physical barrier, such as a mountain range, river, canyon, or glacier.

Sympatric Speciation

The formation of new species within the same geographic area without physical isolation, evolving reproductive isolation in place through polyploidy, microhabitat/resource specialization, or assortative mating.

Polyploidy

The condition of possessing extra sets of chromosomes resulting from nondisjunction during cell division, which can instantly produce reproductive isolation and sympatric speciation in plants.

Prezygotic Reproductive Isolating Mechanisms

Barriers that prevent mating or fertilization between different species, comprising habitat/ecological, temporal, behavioural, mechanical, and gametic isolation.

Postzygotic Reproductive Isolating Mechanisms

Reproductive barriers that operate after zygote formation, including reduced hybrid viability (inviability), reduced hybrid fertility (sterility), and hybrid breakdown in subsequent generations.

Hybrid Breakdown

A postzygotic reproductive isolating mechanism where first-generation ($F_1$) hybrids are viable and fertile, but the offspring of those hybrids ($F_2$ or backcrosses) have reduced fitness or sterility.

Pseudogene

A non-functional, vestigial DNA sequence homologous to functional genes that has accumulated mutations rendering it incapable of producing functional proteins (e.g., dolphins retaining ~$1000$ olfactory genes of which only ~$200$ are functional).

Genetic Drift

Random, non-adaptive fluctuations in allele frequencies from generation to generation caused by chance alone, which exerts a disproportionately powerful effect in small populations.

Bottleneck Effect

A severe reduction in population size and genetic diversity caused by a catastrophic chance event (e.g., dropping from $10\,000$ to $50$ individuals), leaving an unrepresentative sample of surviving alleles.

Founder Effect

A form of genetic drift that occurs when a small group of individuals colonizes a new territory, carrying an unrepresentative allele frequency compared to the original parental gene pool by chance alone.

Hardy-Weinberg Principle

A mathematical null model stating that allele and genotype frequencies remain constant across generations in a non-evolving population, described by $p + q = 1$ and $p^2 + 2pq + q^2 = 1$.

Conditions for Hardy-Weinberg Equilibrium

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

Homologous Structures

Anatomical features shared by different species that are derived from a common ancestral structure due to divergent evolution, although they may serve different present functions.

Pentadactyl Limb

A homologous vertebrate limb architecture characterized by five skeletal segments (humerus, radius/ulna, carpals, metacarpals, and phalanges), conserved across humans, cats, whales, bats, reptiles, and birds.

Analogous Structures

Biological structures that perform similar functions and exhibit superficial similarity due to convergent evolution in response to similar selective pressures, but do not share common evolutionary ancestry.

Vestigial Features

Anatomical structures or organs that have lost most or all of their ancestral function over evolutionary time, such as pelvic bones in baleen whales, hind-limb remnants in snakes, and the human coccyx.

Biogeography

The scientific study of the geographic distributions of living and fossil species, providing evidence for evolution through patterns of mainland resemblance, island colonization, and continental drift.

Divergent Evolution

The evolutionary pattern in which lineages sharing a common ancestor adapt to distinct ecological niches and selective pressures, resulting in divergent morphology and behaviour and generating homologous structures.

Convergent Evolution

The evolutionary process wherein distantly related or unrelated organisms independently evolve similar structures, traits, or functional adaptations in response to similar selective pressures ("similar environment, similar solution").

Co-evolution

A reciprocal evolutionary process ("nature's arms race") in which two or more interacting species exert mutual selective pressures on each other, often developing tight mutualistic, predator-prey, or host-parasite dependencies.

Adaptive Radiation

The rapid evolutionary diversification of a single ancestral species into multiple descendant species that adapt to exploit distinct, unoccupied ecological niches with minimal competition.

Batesian Mimicry

A protective evolutionary strategy where a palatable, harmless species evolves phenotypic traits that closely resemble the warning signals of a toxic, dangerous, or unpalatable model species (e.g., harmless wasp beetle copying a stinging wasp).

Cladogram

A branching phylogenetic diagram representing a hypothesis of evolutionary relationships among taxa, constructed using shared derived characters (synapomorphies).

Clade (Monophyletic Group)

An evolutionary grouping that consists of an ancestral species and all of its descendants.

Sister Taxa

Two phylogenetic lineages or groups that originate from a single immediate common ancestor, making them each other's closest evolutionary relatives on a cladogram.

Outgroup

A closely related species or taxon positioned outside the group of interest that lacks derived characters, used as a reference point to establish ancestral versus derived character states.

Heritability

A population-level statistical measure indicating the proportion of observed phenotypic variation for a specific trait that can be attributed to genetic variation among individuals rather than environmental factors.

Orthologs

Homologous genes found in different species that diverged as a direct consequence of a speciation event, typically retaining the exact same biological function (e.g., insulin genes across humans and mice).

Paralogs

Homologous genes that arise from gene duplication within a genome, allowing one copy to perform the original role while the duplicated copy mutates and diverges to acquire novel functions (e.g., myoglobin and hemoglobin subunits).

Semelparous Strategy

A reproductive life-history strategy in which an organism devotes all its resources to a single massive reproductive event and dies shortly thereafter (e.g., Pacific salmon).