Creationism called "absolutely horrible hypothesis"—statistically speaking.

All life on Earth evolved from a single-celled organism that lived roughly 3.5 billion years ago, a new study seems to confirm.

The study supports the widely held "universal common ancestor" theory first proposed by Charles Darwin more than 150 years ago.

Using computer models and statistical methods, biochemist Douglas Theobald calculated the odds that all species from the three main groups, or "domains," of life evolved from a common ancestor—versus, say, descending from several different life-forms or arising in their present form, Adam and Eve style.

The domains are bacteria, bacteria-like microbes called Archaea, and eukaryotes, the group that includes plants and other multicellular species, such as humans.

The "best competing multiple ancestry hypothesis" has one species giving rise to bacteria and one giving rise to Archaea and eukaryotes, said Theobald, a biochemist at Brandeis University in Waltham, Massachusetts.

But, based on the new analysis, the odds of that are "just astronomically enormous," he said. "The number's so big, it's kind of silly to say it"—1 in 10 to the 2,680th power, or 10 followed by 2,680 zeros.

Theobald also tested the creationist idea that humans arose in their current form and have no evolutionary ancestors.

The statistical analysis showed that the independent origin of humans is "an absolutely horrible hypothesis," Theobald said, adding that the probability that humans were created separately from everything else is 1 in 10 to the 6,000th power.

(As of publication time, requests for interviews with several creationist scientists had been either declined or unanswered.)

Putting Darwin to the Test

All species in all three domains share 23 universal proteins, though the proteins' DNA sequences—instructions written in the As, Cs, Gs, and Ts of DNA bases—differ slightly among the three domains (quick genetics overview).

The 23 universal proteins perform fundamental cellular activities, such as DNA replication and the translation of DNA into proteins, and are crucial to the survival of all known life-forms—from the smallest microbes to blue whales.

A universal common ancestor is generally assumed to be the reason the 23 proteins are as similar as they are, Theobald said.

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That's because, if the original protein set was the same for all creatures, a relatively small number of mutations would have been needed to arrive at the modern proteins, he said. If life arose from multiple species—each with a different set of proteins—many more mutations would have been required.

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