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species

a group of organisms that share similar characteristics and can reproduce among themselves producing fertile offspring.

evolution

change in inherited characteristics over time.

natural selection

a process by which organisms with traits best suited to their environment are more likely to survive and reproduce; includes concepts of variation, overproduction, and competition.

variation

inherited trait that makes an individual different from other members of the same species and results form a mutation in the organism's genes.

adaptation

any variation that makes an organism better suited to its environment.

gradualism

model describing evolution as a slow process by which one species changes into a new species through a continuing series of mutations and variations over time.

punctuated equilibrium

model describing the rapid evolution that occurs when mutation of a few genes results in a species suddenly changing into a new species.

sedimentary rock

a type of rock, such as limestone, that is most likely to contain fossils and is formed when layers of sand, silt, clay, or mud are cemented and compacted together or when minerals are deposited from a solution.

radioactive element

element that gives off a steady amount of radiation as it slowly changes to a nonradioactive element.

embryology

study of embryos and their development.

homologous

body parts that are similar in structure and origin and can be similar in function.

vestigial structure

structure, such as the human appendix, that doesn't seem to have a function and may once have functioned in the body of an ancestor.

primates

group of mammals including humans, monkeys, and apes that share characteristics such as opposable thumbs, binocular vision, and flexible shoulders.

hominid

humanlike primate that appeared about 4 million to 6 million years ago, ate both plants and meat, and walked upright on two legs.

Homo sapiens

early humans that likely evolved from Cro-Magnons.

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