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Hypothesis 1: Phyletic gradualism - slow and steady divergence of lineages. The "burst" of evolution is a geological illusion. It only looks like a burst because a lot of time — say, 5 million years — passed between the times when the two rock layers were laid down. In this period of time, species 3 gradually diverged from ancestor 1 through a series of transitional forms, but these transitional forms were not preserved.
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Pace of evolution hypotheses (1 of 4)
In many cases, we seem to observe "bursts" of evolution in the fossil record. In this example, in a lower rock layer, you see ancestor 1. In the next rock…
Pace of evolution hypotheses (3 of 4)
Hypothesis 2: Punctuated equilibrium — a large amount of change in a short time, tied to a speciation event. Species 2 and 3 are only 100,000 years younger than ancestor…