Chapter 4

Biological species concept

A species is a group that can interbreed and produce viable, fertile offspring.

Species

A group of organisms capable of successful interbreeding.

Viable offspring

Offspring capable of surviving.

Fertile offspring

Offspring capable of reproducing.

Reproductive isolation

Populations cannot successfully interbreed or exchange genes.

Speciation

The formation of new species.

Cladogenesis

One species splits into two or more species.

Anagenesis

One species gradually changes into another without branching.

Gene flow

Movement of genes between populations through reproduction.

Splitter

A scientist who tends to recognize more separate species.

Lumper

A scientist who tends to combine populations into fewer species.

Allopatric speciation

Speciation caused by geographic separation.

Parapatric speciation

Neighboring populations diverge while some gene flow continues.

Sympatric speciation

Speciation that occurs in the same geographic area.

Geographic isolation

Physical separation of populations by a geographic barrier.

Prezygotic barrier

A barrier that prevents mating or fertilization before a zygote forms.

Postzygotic barrier

A barrier in which hybrids have reduced survival or fertility after fertilization.

Zygote

The fertilized cell formed when sperm and egg join.

Hybrid

Offspring produced from genetically different populations or species.

Reinforcement

Natural selection strengthens reproductive isolation when hybrids have low fitness.

Character displacement

Competition causes coexisting species to become more different.

Adaptive radiation

One ancestral species rapidly diversifies into many specialized species.

Ecological niche

A species' role and resource use in its environment.

Microevolution

Evolutionary change within a population over generations.

Macroevolution

Large-scale evolutionary change at or above the species level.

Mass extinction

A rapid, widespread loss of many species across many groups.

Plate tectonics

Movement of Earth's plates that changes geography and habitats.

Cambrian explosion

A rapid diversification of many major animal groups during the Cambrian.

Darwinian gradualism

Evolution occurs through slow, continuous change over long periods.

Punctuated equilibrium

Long periods of little change interrupted by relatively rapid evolutionary change.

Phylogeny

The evolutionary history and relationships among organisms.

Phylogenetic tree

A branching diagram showing evolutionary relationships.

Common ancestor

An ancestral population shared by two or more lineages.

Branch point / node

A point on a phylogenetic tree representing a common ancestor and lineage split.

Descent with modification

Descendants inherit ancestral traits but change over generations.

Hierarchy

A system in which smaller groups are contained within larger groups.

Homologous structure

A similar structure inherited from a common ancestor.

Analogous trait

A similar trait that evolved independently rather than from common ancestry.

Convergent evolution

Similar traits evolve independently in different evolutionary lineages.

Ancestral trait

A trait present in an older common ancestor.

Derived trait

A newer trait that evolved after a lineage diverged.

Shared derived trait

A derived trait shared by related species because of a more recent common ancestor.

Out-group

A related outside group used to identify ancestral and derived traits.

Genetic distance

A measure of genetic differences between organisms or species.

Molecular clock

A method using rates of genetic change to estimate divergence time.

Fossil calibration

Using fossil dates to estimate the rate of molecular evolution.

Taxonomy

The naming and classification of organisms.

Systematics

The study and reconstruction of evolutionary relationships.

Comparative method

Comparing species while accounting for shared ancestry.

Genus

A taxonomic group containing closely related species.

Family

A taxonomic group containing closely related genera.

Superfamily

A taxonomic group containing closely related families.

Pan

The genus containing chimpanzees and bonobos.

Pan troglodytes

The scientific name for the common chimpanzee.

Pan paniscus

The scientific name for the bonobo.

Cladistic taxonomy

Classification based primarily on common ancestry and branching relationships.

Evolutionary taxonomy

Classification based on common ancestry plus overall similarity.

Locomotion

The way an organism moves.

Bipedal

Moving primarily on two legs.

Quadrupedal

Moving primarily on four limbs.

Knuckle walking

Locomotion using the knuckles to support body weight.

Arboreal

Tree-dwelling.

Terrestrial

Ground-dwelling.

Hominoid

An ape; includes humans and nonhuman apes.

Great apes

Orangutans, gorillas, chimpanzees, bonobos, and humans.

Lesser apes

Gibbons and siamangs.

Common ancestry

The idea that different species descended from shared ancestral populations.

Divergence

The evolutionary separation of lineages over time.

Earliest life on Earth

The first known life forms were simple microorganisms, long before complex animals appeared.