Evolutionary Patterns and Processes

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Macroevolutionary Pattern Noun

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Macroevolutionary Pattern

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A large-scale evolutionary trend that occurs over long periods, such as the emergence or extinction of major taxonomic groups.

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Example: This diagram shows how three-color vision evolved independently in two different primate groups, an example of convergent evolution, which is a macroevolutionary pattern.

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Background Extinction Noun

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Background Extinction

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The standard, continuous rate of species extinction that occurs over geologic time, separate from catastrophic mass extinction events.

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Example: This graph shows that background extinction is the normal, low-level rate of species loss, which is much lower than the sharp spikes of mass extinctions.

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Mass Extinction Noun

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Mass Extinction

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An event where a large number of species die out globally over a relatively short time, causing a sharp biodiversity decrease.

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Example: This graph shows that a mass extinction is a period when the rate of extinction (the sharp spikes) dramatically increases above the normal background extinction rate.

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Gradualism Noun

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[graj-oo-uh-liz-uhm]

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Gradualism

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A model of evolution which theorizes that profound change is the cumulative product of slow but continuous processes over time.

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Example: This image shows how a species can slowly change over a long time, with small, gradual steps leading to significant differences, like these insects evolving to look like leaves.

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Punctuated Equilibrium Noun

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Punctuated Equilibrium

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An evolutionary pattern where long, stable periods of little change are interrupted by brief periods of more rapid speciation.

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Example: This diagram shows how a species can remain unchanged for long periods (stasis), followed by a short burst of fast evolutionary change.

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Adaptive Radiation Noun

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Adaptive Radiation

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The process where a single species or small group evolves over a short time into several different forms living differently.

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Example: From one common ancestor, different species evolve to have specialized traits, like varied beak shapes, to take advantage of different food sources in an environment.

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Convergent Evolution Noun

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Convergent Evolution

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The process where unrelated organisms independently evolve similar traits when adapting to similar environments or ecological niches.

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Example: Unrelated species, like sharks (fish) and dolphins (mammals), independently evolve similar traits, such as streamlined bodies, to adapt to similar environments or needs.

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Coevolution Noun

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[koh-ev-uh-loo-shuhn]

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Coevolution

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The process by which two or more species reciprocally affect each other's evolution in response to changes in one another.

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Example: This diagram shows how a moth and a flower evolve together; as the flower's tube gets longer, moths with longer tongues are more successful, driving both to change.

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Macroevolution Noun

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Macroevolution

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Major evolutionary change, such as the origin of new groups of organisms, that occurs at or above the species level.

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Example: This diagram shows how a single ancestral species can branch out into many different species over millions of years, which is macroevolution.

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Stasis Noun

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[stey-sis]

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Stasis

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A period of little or no observable evolutionary change in a species' physical structure, as documented in the fossil record.

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Example: This diagram shows that snail fossils found in older, deeper rock layers are identical to the snails living today, illustrating a long period of no evolutionary change.