Nicolle Rager Fuller / NSF

An artist's conception shows an RNA molecule, which may have served as an early form of life on Earth.

By Alan Boyle

The debate over the definition of life is getting messier and messier, but one of the pioneers on the biochemical frontier is suggesting a method to tell whether scientists are actually looking at a new form of life: Follow the bits of information that are contained in the chemistry.

"How many heritable 'bits' of information are involved, and where did they come from?" Scripps Research Institute biologist Gerald Joyce asks in an essay published today by the journal PLoS Biology. "A genetic system that contains more bits than the number that were required to initiate its operation might reasonably be considered a new form of life."

By that definition, we're not yet close to identifying alien life, in the lab or in the cosmos, Joyce told me today."The fact is, there is only one known form of life, and we're part of it. Someday, maybe there'll be something that's off the grid, but everything we know is part of the tree of life."

Joyce says that verdict applies to microbes with artificially constructed DNA, such as the bacteria that were built in a lab two years ago, as well as to the arsenic-tolerant bacteria that were at one time touted as a form of alien life. Heworries that all these claims about creating or finding alien life could backfire.

"We've had enough of these false alarms that I'm getting a little nervous that the public is going to perceive it as 'crying wolf,'" he said. "There have been enough examples that we need to just cool it a little."

Joyce applies the same rule of thumb to his own research, which focuses on RNA enzymesthat can be combined to create a synthetic genome. In the essay, he notes that the RNA enzymes can "evolve" into new forms, but contain only 24 bits of their own heritable information in the form of chemical base pairs. The molecules need another 60 bits of information that are provided at the outset and are not subject to mutation and selection.

"Thus, of the 84 total bits required for the system to replicate and evolve, only about one-fourth can be counted as part of the system's molecular memory," he writes. "The synthetic genetic system is not a new life form because it operates mostly on borrowed bits."

Go here to see the original:
What is life? Follow the bits