Natural Selection, Evolution, and Ecology Flashcards

Comprehensive vocabulary flashcards covering Natural Selection, Cladistics, Speciation, and Population Ecology based on the IB Biology First Assessment 2025 Study Guide.

Natural Selection

The core mechanism driving evolutionary change where individuals with favorable heritable traits survive and reproduce more, leading to changes in allele frequencies over time.

Lamarckism

The incorrect theory that changes acquired during an individual's lifetime, such as a bodybuilder's muscles, can be inherited by offspring.

Paradigm Shift

A revolutionary change in scientific thinking, such as when Darwin's theory of natural selection replaced Lamarckism.

Mutation

Random changes to DNA sequences that create brand new alleles; it is the ultimate source of all new genetic variation.

Selection Pressure

Any factor in the environment, whether biotic (predation, disease) or abiotic (temperature, drought), that affects an individual's survival or reproduction.

Fitness

The ability of a genotype to survive and reproduce in a given environment, specifically measured by leaving the most offspring.

Directional Selection

A type of natural selection where one extreme of the trait range is favored, such as antibiotic resistance in bacteria.

Stabilising Selection

A type of natural selection where the average trait is favored and extremes are eliminated, such as human birth weight.

Disruptive Selection

A type of natural selection where both extremes are favored over the average, which can split a population into two distinct groups.

Sexual Selection

Selection for traits that increase mating success, such as peacock tails, even if those traits may reduce overall survival.

Gene Pool

The total collection of all genes and all their alleles present in a population.

Neo-Darwinism

The modern integration of genetics with Darwin's theory of natural selection.

Hardy-Weinberg Equation: Allele Frequencies

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

Hardy-Weinberg Equation: Genotype Frequencies

$p^2 + 2pq + q^2 = 1$, where $p^2$ is homozygous dominant, $2pq$ is heterozygous, and $q^2$ is homozygous recessive.

Artificial Selection

The process where humans deliberately choose individuals with desirable traits for breeding in crops and livestock.

Cladistics

A method of classifying organisms based on their evolutionary history and shared common ancestry rather than morphological appearance.

Clade

A group of organisms that includes a common ancestor and all of its descendants, defined by molecular or morphological data.

Root (Cladogram)

The base of a cladogram representing the common ancestor of all organisms shown in the diagram.

Node (Cladogram)

A branching point on a cladogram that represents a hypothetical common ancestor of the lineages above it.

Parsimony Analysis

The principle of choosing the cladogram that requires the fewest total mutations to explain observed differences.

Molecular Clock

The use of the rate of DNA or protein sequence divergence to estimate when a common ancestor lived.

Three Domains

The classification level above kingdoms proposed by Carl Woese in 1977, consisting of Bacteria, Archaea, and Eukarya.

Evolution

The change in the heritable characteristics of a population over generations.

Homologous Structures

Structures that share the same underlying anatomy but have different functions, such as the pentadactyl limb, providing evidence of common ancestry.

Analogous Structures

Structures with the same function but different evolutionary origins, such as bird and insect wings, resulting from convergent evolution.

Speciation

The formation of new and distinct species from a pre-existing species through reproductive isolation and differential selection.

Allopatric Speciation

Speciation that occurs when populations become geographically separated by physical barriers like mountains or rivers.

Sympatric Speciation

Speciation that occurs within the same geographic area without physical separation, often through behavioral or temporal isolation.

Adaptive Radiation

The rapid evolution of many new species from a single common ancestor to fill different ecological niches.

Polyploidy

A condition where an organism has more than two sets of chromosomes, which can cause abrupt speciation in plants.

Population

A group of organisms of the same species living in the same area at the same time that normally interbreed.

Lincoln Index

A formula used to estimate population size for motile organisms: N = rac{M imes n}{R}, where $M$ is the number marked in the first catch, $n$ is the total in the second catch, and $R$ is the number of marked individuals recaptured.

Carrying Capacity (K)

The maximum population size that an environment can sustainably support given its available resources.

Density-dependent Factors

Factors like competition, predation, and disease that increase in intensity as population density increases, helping to regulate population size.

Density-independent Factors

Factors such as floods, fires, or harsh weather that affect individuals regardless of the population's size.

Community

All the interacting organisms of different species living together in an ecosystem.

Mutualism

An interspecific interaction where both species benefit, such as Rhizobium bacteria in root nodules or zooxanthellae in corals.

Allelopathy

The release of chemicals by a plant into the soil to inhibit the germination or growth of competing plants.

Invasive Species

An introduced species that outcompetes endemic species due to a lack of predators or superior competitive ability.

Top-Down Control

A situation where predators at the top of the food web regulate the size of the populations below them.