A gene that controls when protein-coding genes are turned on or off.

The idea that, in order for a species to maintain a particular niche in an ecosystem and its fitness relative to other species, that species must be constantly undergoing adaptive evolution because the organisms with which it is coevolving are themselves undergoing adaptive evolution. When species evolve in accordance with the Red Queen hypothesis, it often results in an evolutionary arms race.

A situation in which an altruistic behavior (one that represents a fitness cost to the actor and a fitness benefit to the receiver) is likely to be reciprocated in the future by another individual in the population, benefitting the original altruist. Reciprocal altruism can help explain how cooperation and altruism in general can evolve via natural selection.

Gene version with an effect that is only observed when it is found paired with an identical version in the same individual.

Unpredictable in some way. Mutations are “random” in the sense that the sort of mutation that occurs cannot generally be predicted based upon the needs of the organism. However, this does not imply that all mutations are equally likely to occur or that mutations happen without any physical cause. Indeed, some regions of the genome are more likely to sustain mutations than others, and various physical causes (e.g., radiation) are known to cause particular types of mutations.

A mating system in which an individual is equally likely to mate with any other individual in the population, regardless of the individual’s genotype.

A method of determining the date at which an igneous rock solidified based upon the rate of decay of radioactive atoms within the rock. For a more detailed explanation see our resource on radiometric dating.

A property of an item (e.g., a shape or an animal) that can be divided into two matching halves by many different lines, which all intersect one another at a single point in the center. For example, pies, snowflakes, and starfish are radially symmetric because they have many different lines of symmetry (dividing them into matching halves) and the lines cross one another at the center.

A way of classifying humans into large groups based on inherited characteristics, physical appearance, and many other factors. While it is true that some groups of humans share large portions of their evolutionary history (and that this shared evolutionary history has biological implications), scientists agree that there is no biological basis for dividing Homo sapiens into discrete “races,” as they have been socially defined. For more details, see our resource on genetic variation and ethnicity in Evolution 101 or our news story on why evolutionary history matters.

A process in which pairs of chromosomes swap DNA with one another. This happens during gamete formation. A single parent cell (containing two sets of chromosomes) will form four daughter cells (with one complete set of chromosomes each). In the process of forming these daughter cells, recombination happens so that the chromosomes the daughter cells have are “mosaic,” composed of different pieces of the parent cells’ chromosomes. Recombination is important for evolution because it brings new combinations of genes together — a source of variation for natural selection to act upon.

Ribonucleic acid, a molecule similar to DNA involved in carrying information and producing proteins in cells. Some viruses carry RNA as their genetic material instead of DNA.