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What happens when animals evolve in isolation?

        Science | Evolution

Gradual vs. Punctual
China has provided a large number of fossils to the fossil record -- the natural history of Earth captured by all of the fossilized remains discovered to this point. This skeleton was displayed in Shanghai in July 2007.
China has provided a large number of fossils to the fossil record -- the natural history of Earth captured by all of the fossilized remains discovered to this point. This skeleton was displayed in Shanghai in July 2007.
China Photos/Getty Images

It seems that when members of a species end up isolated from other members of their species a speciation event is likely to occur. Scientists can compare the genes of similar species to show that the common DNA they share strongly suggests the two species were previously one. But how does this process occur? Unfortunately, evolutionists haven't been able to pin down exactly how speciation takes place. Instead, two main camps have evolved, so to speak, with very different opinions on how the process of speciation takes place.

There are those who believe in phyletic gradualism, the thought that the process of speciation takes place constantly and over long periods of time. Others believe in punctuated equilibrium. These people believe that speciation takes places in quick jumps and starts, with long periods of time between events. Both groups have the fossil record to contend with.

The fossil record is the sum total of all of the fossils that have been discovered thus far. Placed together, they form a relatively clear picture of the evolution of life on Earth. But there are, however, gaps in the fossil record -- periods when new species suddenly emerge without any apparent transition from one species to a radically different, related species.

Those who subscribe to punctuated equilibrium say the fossil record is proof their theory concerning speciation is the correct one. If speciation takes place in sudden jumps and starts, there should be no record of transition from one species to a sister species. Instead, members of a species find themselves reproductively isolated from other members and suddenly, speciation occurs.

For the part of the gradualists -- who generally claim among their ranks Charles Darwin, the father of evolutionary theory -- the fossil record is simply incomplete. The process of speciation includes a long transition from one species to a related species. In the gradualists' eyes, these transition members simply haven't been culled from the layers of silt and rock in the Earth yet. In other words, the fossil record, to the gradualists, is simply incomplete.

But the dispute over how speciation happens may be put to rest. A perfect natural experiment has literally washed ashore. And the setting couldn't be more perfect. To find about it, read the next page.


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