A theory in crisis!

A theory in crisis.

A team of Canadian and French scientists has shed new light on what’s being called the Earth’s “last universal common ancestor,” the 3.8-billion-year-old microscopic organism from which all living things – bacteria and humans and sunflowers alike – evolved.

The researchers, including Universite de Montreal evolutionary geneticist Nicolas Lartillot and colleagues from the Universite de Lyon, say they’ve discovered that “LUCA” was not the heat-craving entity scientists have traditionally believed it to be. Instead, the team argues in the journal Nature, the primitive speck of life that became mother and father to all plants and animals preferred relatively cool temperatures of less than 50 C – not the 90 C habitat generally assumed to be its ideal simmering temperature in life’s primordial soup.

“It is generally believed that LUCA was a heat-loving or ‘hyperthermophilic’ organism – a bit like one of those weird organisms living in the hot vents along the continental ridges deep in the oceans today,” said Nicolas Lartillot, a bio-informatics professor at the U de M. “However, our data suggests that LUCA was actually sensitive to warmer temperatures and lived in a climate below 50 degrees.”

The study states that the initial offspring lineages of the common ancestral life form must have adapted later to higher temperatures, “possibly in response to a climate change of the early Earth.”

The study provides a new look at the planet’s biological beginnings – even before the rudimentary chemical ingredients of life had assembled into DNA strands that would become fundamental to evolution.

“The group’s findings are an important step toward reconciling conflicting ideas about LUCA,” a research summary states. “In particular, they are much more compatible with the theory of an early RNA world, where early life on Earth was composed of ribonucleic acid (RNA), rather than deoxyribonucleic acid (DNA).”

The researchers note that heat-sensitive RNA was “unlikely to be stable in the hot temperatures of the early Earth” but that LUCA must have found “a cooler micro-climate” in which to develop.

“It is only in a subsequent step that LUCA’s descendants discovered the more thermostable DNA molecule, which they independently acquired (presumably from viruses), and used to replace the old and fragile RNA vehicle,” Lartillot said in the statement. “This invention allowed them to move away from the small, cool micro-climate, evolve and diversify into a variety of sophisticated organisms that could tolerate heat.”

Oh, hang on. It looks like scientists are just debating how evolution occurred, not whether it occurred. Business as usual.

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