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absolute age

the actual age in years of a fossil

acquired trait

a trait not determined by genes but arising as a result of experience or behavior


in populations, to change genetically over generations to become more suited to the environment


an inherited trait that increases an organism's chance of survival in a particular environment

adaptive advantage

a favorable trait in an organism

adaptive radiation

an evolutionary pattern in which many species evolve from a single ancestral species

analogous structure

in evolution, structures in more than one organism that have similar appearance and function but different embryological origins

artificial selection

breeding of organisms by humans for specific phenotypic characteristics


study of the geographical distribution of fossils and living organisms


a type of fossil formed when sediments fill in the cavity left by a decomposing organism


the mutual evolution of two different species interacting with each other


the act of preserving genes that remain unchanged in DNA

convergent evolution

the process by which unrelated species become more similar as they adapt to the same kind of environment

divergent evolution

the process of two or more related species becoming more and more dissimilar


the dying out of a species


a measurement of the ability of a species to respond to the pressures of natural selection; the ability of individuals to survive to propagate their genes


the remains or traces of a once-living organism


features similar features that originated in a shared ancestor

law of superposition

a law that states that successive layers of rock or soil were deposited on top of one another and the lowest level is oldest

mass extinction

one of the brief periods of time during which large numbers of species disappeared


a type of fossil formed from an impression of the shape or tracks of an organism; in fungi, a mass of tangled filaments of cells, such as the fungus that grows on bread

natural selection

the process by which organisms with favorable variations reproduce at higher rates than those without such variations


all the members of a species that live in the same area and make up a breeding group

relative age

the comparative ages of fossils found within a single stratum


dust, sand, or mud deposited over time by wind or water


in geology, a layer of soil or rock in a cross section of the Earth


a principle that states that the geological structure of Earth resulted from cycles of observable processes and that these processes operate continuously


referring to a functionless structure that was functional in an ancestral species

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