Final

Evolutionary stable strategy (ESS)

A phenotype that cannot be replaced by any other phenotype under specified conditions.

Game theory

A branch of mathematics concerned with analyzing strategies for dealing with competitive situations whose outcomes depend on the actions of other participants.

Assessor strategy

Escalates a conflict if opponent is judged to be smaller or weaker; retreats if opponent is larger or stronger.

Honest signal

Information that is a true indicator of the underlying quality of the sender and is useful to the receiver.

Altruism

An activity that enhances the fitness of other individuals but lowers the fitness of the actor.

Reciprocation

A behavior where an organism acts in a manner that reduces its fitness while increasing another organism's fitness, expecting similar behavior later.

Manipulation

Donor dispenses aid because the donor is being manipulated by the recipient.

Individual advantage

Cooperative behavior may evolve because it is advantageous to the individual.

Reciprocal altruism

A behavior whereby an organism reduces its fitness to increase another's fitness with an expectation of future reciprocation.

Prisoner's dilemma

A thought experiment involving two rational agents choosing between cooperation for mutual benefit or betrayal for individual reward.

Direct fitness

The effect of fitness of an allele on the individual that has it.

Indirect fitness

The effect of fitness of an allele on other individuals sharing the allele.

Inclusive fitness

The total effect of an allele on the fitness of both the individual that has it and other individuals that share the allele.

Hamilton's Rule

An altruistic trait increases in frequency if the benefit to the donor's relatives exceeds the cost to the donor's fitness; rb > c.

Eusociality

The highest level of organization of animal sociality characterized by cooperative brood care, overlapping generations, and division of labor.

Coevolution

When two or more species reciprocally affect each other's evolution through natural selection.

Red Queen hypothesis

The theory that species must continually evolve to survive due to the ongoing evolution of other associated species.

Oparin-Haldane hypothesis

Suggests that life arose gradually from inorganic molecules, with simple building blocks forming first.

Miller-Urey experiment

Provided evidence that organic molecules necessary for life could be formed from inorganic components.

RNA world hypothesis

The theory that the first life forms were self-replicating RNA.

The six major evolutionary transitions

Key changes in evolution including the development of genomes, multicellular organisms, and eusocial societies.

Strata

Sedimentary layers that can be distinguished using distinctive fossil taxa.

Radiometric dating

A method of dating ancient rock layers by measuring the decay of radioactive elements.

Endosymbiosis theory

The theory that some organelles in eukaryotic cells were once free-living prokaryotic microbes.

Cambrian explosion

A relatively short evolutionary event starting around 542 million years ago when most major animal phyla appeared.

Diapsids

Vertebrates with two temporal fenestrae, including dinosaurs and birds.

Synapsids

Vertebrates with a single temporal fenestra, including mammals.

Refugia

Areas with isolated populations that were previously broadly distributed.

Microevolution

Evolutionary processes that occur within species.

Macroevolution

Evolution above the species level including rates of evolution and diversification of higher taxa.

Gradualism

The hypothesis that evolution proceeds gradually over time.

Punctuated equilibrium

A model of evolution characterized by long periods of stasis followed by short periods of rapid change.

Habitat tracking

The shifting of species' geographic distributions in response to changes in their habitat.

Saltation

Sudden evolutionary changes that occur in a single generation.

Living fossils

Organisms that have changed little over millions of years, resembling their ancient ancestors.

Phylogenetic niche conservatism

The tendency of species to retain ancestral traits and maintain dependence on similar resources and environments.

The five mass extinctions

Major extinction events that significantly reduced Earth's biodiversity.

Background extinction rate

The normal extinction rate outside of mass extinction events, estimated to be around 1 extinction per million species years.

Evolutionary trend

A persistent, directional change in the average value of a feature within a lineage.

Passive trend

Lineages in a clade evolve in both directions with equal probability.

Active (or driven) trend

Changes in one direction are more likely than changes in the other.

Possible causes for evolutionary trends

1) Individual selection favoring a phenotype, 2) extinction rates favoring larger sizes, 3) recent speciation events being more frequent in larger clades.

Predictability of evolutionary paths

The evolutionary history of life can be seen as inevitable due to widespread evolutionary parallelism and convergence.

Contingency of evolutionary paths

The notion that the path of evolution has been shaped by chance events.