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a structure, trait or behavior that improves an organism's chance of survival


an early kind of animal from which later ones have developed; a forerunner.


to hide by blending in with surroundings


the process of grouping things based on their similarities


the struggle between organisms to survive in a habitat with limited resources


a person or animal that is descended from a specific ancestor; an offspring.


the gradual change in a species over time


The evolutionary termination of a species caused by the failure to reproduce and the death of all remaining members of the species

Fossil record

a historical sequence of life indicated by fossils found in layers of the Earth's crust

Evolutionary fitness

the probability that the line of descent from an individual with a specific trait will survive


the remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil


a model of evolution in which gradual change over a long period of time leads to biological diversity

Homologous structures

Structures in different species that are similar because of common ancestry.


a grouping system that divides organisms into 6 major categories

Natural selection

process by which individuals that are better suited to their environment survive and reproduce most successfully; also called survival of the fittest


new organisms produced by a living thing


organisms produce more offspring than can survive

Punctuated equilibrium

long periods of stability are interrupted by short episodes of rapid species formation


a group of organisms that are closely related and can mate to produce fertile offspring

Survival of the Fittest

The ones who survive are the ones best adapted to exist in their environment and to on to reproduce.


A well-tested concept that explains a wide range of observations.


Different characteristics of the individuals in any one species.

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