[LINK] "Life on Earth Arose Just Once"

[rfmcdonald]

Does all life on Earth descend from a single ancestor? According to this Wired Science report, yes, it did.

For his analysis, [biochemist Douglas] 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,” Theobald says.

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.

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,” Penny says. “But what it does say is that there was one common ancestor among all those little beasties.”

The article doesn't note that there might also be life forms as yet undiscovered with different ancestries, perhaps in environments wildly different from the ones we encounter, buried deep in the Earth's crust, say.