Biology: punctuated equilibrium and the fossil record

Tutoring biology, ideas about evolution arise. The tutor mentions punctuated equilibrium.

Punctuated equilibrium suggests that, during the process of evolution, a species might remain relatively unchanged for a long period (the equilibrium), then suddenly undergo a period of rapid change (punctuation).

One concept that drives the idea of punctuated equilibrium is the fact that fossils of transitional species seem so hard to find. Let’s assume the belief that species B evolved from species A. Evolution imagines a species of description A/B in between, apparently on its way to becoming B. Yet, fossils of such species seem largely absent, which surprised Darwin.

Therefore, in 1972, Gould and Eldredge proposed punctuated equilibrium as a way to uphold the theory of evolution in spite of the lack of transitional fossils. Their ideas are as follows:

• A successful species likely lives in a stable environment where its survival is easy, so its population large. This condition will likely be long-term and produce a high number of fossils.
• Evolutionary pressure will happen in situations where the environment doesn’t support the species. For example, a sudden environmental change could cause evolutionary pressure.
• A new species probably won’t originate on a “mainstream” basis. Rather, it will probably originate from a few marginal members of the population who change in a particularly helpful way.
• With evolutionary pressure high, and the numbers successfully adapting relatively low, few individuals will be available to produce transition fossils. Moreover, said fossils just as likely won’t be found in the same place as most of the originating population’s fossils, but rather somewhere along the margin of its geographic range.
• Once the adapting group has changed enough to become fit for survival, it will likely already manifest as the new species. From then on, its reproduction rate will be high, so its fossils easy to find.

Source:

pbs.org

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