Gradualism and Punctuated Equilibrium

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Gradualism Noun

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[grad-joo-uh-liz-um]

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Gradualism

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The hypothesis that the evolution of a species occurs gradually over time as a slow and constant process of change.

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Example: This diagram shows gradualism, where a species changes slowly and steadily over a long time, resulting in a fossil record with many intermediate forms.

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Punctuated Equilibrium Noun

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[punk-choo-ay-tid ee-kwuh-lib-ree-um]

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Punctuated Equilibrium

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An evolutionary model defined by long periods of stability, or stasis, which are interrupted by sudden, rapid species change.

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Example: This diagram shows that species can stay the same for long periods of time (stasis) and then experience short bursts of rapid evolutionary change.

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Divergent Evolution Noun

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[di-vur-junt ev-uh-loo-shun]

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Divergent Evolution

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The process where groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species.

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Example: This diagram shows that two different species, the modern elephant and the extinct mammoth, both evolved from a single common ancestor, demonstrating divergent evolution.

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Convergent Evolution Noun

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[kun-vur-junt ev-uh-loo-shun]

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Convergent Evolution

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The process where unrelated organisms independently evolve similar traits as a result of adapting to similar environments or ecological niches.

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Example: This diagram shows that different, unrelated groups (represented by colored arrows) can evolve similar traits or structures when adapting to similar environments or pressures.

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Coevolution Noun

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[ko-ev-uh-loo-shun]

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Coevolution

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The process where two or more species reciprocally affect each other's evolution, often in a predator-prey or host-parasite relationship.

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Example: A sword-billed hummingbird's long beak has evolved to match the long, tubular shape of a flower, showing how two species influence each other's evolution.

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Speciation Noun

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[spee-see-ay-shun]

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Speciation

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The evolutionary process by which populations evolve to become distinct species that are reproductively isolated from one another.

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Example: This diagram compares two ways new species can form: Gradual Speciation, with slow, steady changes over time, and Punctuated Equilibrium, with long stable periods followed by rapid change.

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Stasis Noun

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[stay-sis]

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Stasis

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A long period in the fossil record during which a species shows little or no evolutionary change or morphological divergence.

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Example: This diagram shows that a species of snail has not changed its physical form over a long period, as seen by comparing living snails to their fossils in different rock layers.

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Mass Extinction Noun

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[mas ik-stingk-shun]

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Mass Extinction

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A catastrophic event that causes a large number of different species across the globe to disappear in a short time.

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Example: This diagram shows that mass extinctions, which are key events in punctuated equilibrium, can be caused by many different factors like meteorite impacts and volcanism.