All modern life on Earth originated from common ancestor

Last Updated: Monday, May 17, 2010 - 13:00

Washington: All life on Earth in today’s date must have stemmed from a common ancestor rather than multiple sources, suggests a new statistical analysis.

Scenarios featuring a universal common ancestor won hands down against even the best-performing multi-ancestor models.

The idea that life forms share a common ancestor is "a central pillar of evolutionary theory. But recently there has been some mumbling, especially from microbiologists, that it may not be so cut-and-dried," Discovery News quoted Douglas Theobald, a biochemist at Brandeis University in Waltham, Mass., as saying.

Because microorganisms of different species often swap genes, some scientists have proposed that multiple primordial life forms could have tossed their genetic material into life`s mix, creating a web, rather than a tree of life.

To determine which hypothesis is more likely correct, Theobald put various evolutionary ancestry models through rigorous statistical tests.

The results weigh more towards on the side of a single ancestor.

A universal common ancestor is at least 102,860 times more probable than having multiple ancestors, calculated Theobald.

No one has previously put this aspect of evolution through such a stringent test, said David Penny, a theoretical biologist at Massey University in Palmerston North, New Zealand.

"In one sense, we are not surprised at the answer, but we are very pleased that the unity of life passed a formal test," he said.

For his analysis, Theobald selected 23 proteins that are found across the taxonomic spectrum but have structures that differ from one species to another.

He looked at those proteins in 12 species— four each from the bacterial, archaeal and eukaryotic domains of life.

Then he performed computer simulations to evaluate how likely various evolutionary scenarios were to produce the observed array of proteins.

Theobald found that scenarios featuring a universal common ancestor won hands down against even the best-performing multi-ancestor models.

"The universal common ancestor (models) didn`t just explain the data better, they were also the simplest, so they won on both counts," said Theobald.

A model that had a single common ancestor and allowed for some gene swapping among species was even better than a simple tree of life.

Such a scenario is 103,489 times more probable than the best multi-ancestor model, Theobald found. That``s a 1 with 3,489 zeros after it.

Theobald`s study does not address how many times life may have arisen on Earth. Life could have originated many times, but the study suggests that only one of those primordial events yielded the array of organisms living today.

"It doesn`t tell you where the deep ancestor was. But what it does say is that there was one common ancestor among all those little beasties," said Penny.

The study has been published in the latest issue of Nature.

ANI



First Published: Monday, May 17, 2010 - 13:00

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