Sometimes, New Scientist puts a strange twist on their stories — like this one, Universal ancestor of all life on Earth was only half alive. I got stuck on just the title. “Half alive”? What does that mean? It’s describing a paper that did a comparative analysis of genes found in 1800 bacteria and 130 archaea to identify what was common between them, which would suggest what genes were present in the last universal common ancestor.
Now we have the best picture yet of what that ancestor was like and where it lived, thanks to a study that identified 355 genes that it probably possessed.
“It was flabbergasting to us that we found as many as we did,” says William Martin of the University of Dusseldorf in Germany, who led the study. The findings support the idea that the last universal common ancestor (LUCA) lurked in hydrothermal vents where hot water rich in hydrogen, carbon dioxide and minerals emerged from the sea floor.
“It’s spot on with regard to the hydrothermal vent theory,” Martin says. He describes LUCA as half-living, because it may have depended on abiotic reactions in the vents to produce many of the chemicals it needed.
That last bit is where they lost me. I’m about 0.4% salt, which is abiotically derived…does that mean I’m only 99.6% alive? And what about water? I’m 60% water, which means I’m now 39.6% alive, or mostly dead. If you’re just talking about chemical reactions, I don’t have an autonomous power source, but rely on daily input of organic material produced by other living creatures. So by that definition, I am a mostly dead, or undead, zombie PZ that lives by ghoulishly feasting upon the bodies of the living.
When I put it that way, it doesn’t sound so bad.
But I think what is messing us up here is a continuing bias towards vitalism — there is no distinction between “life” and “chemistry”. If you just accept that, we’ll all stop wasting our time trying to figure out what part of our biology is life vs. not-life. This video is a nice simplified approach to the problem of the origin of life, but it also seems hung up on a pointless distinction between “dead chemicals” and “living cells”.
At least the story does make the case for the increasingly dominant hypothesis for the origin of life on earth — that it came from reactions that exploited electron gradients found at deep-sea hydrothermal vents.
One characteristic of almost all living cells is that they pump ions across a membrane to generate an electrochemical gradient, then use that gradient to make the energy-rich molecule ATP. Martin’s results suggest LUCA could not generate such a gradient, but could harness an existing one to make ATP.
That fits in beautifully with the idea that the first life got its energy from the natural gradient between vent water and seawater, and so was bound to these vents. Only later did the ability to generate gradients evolve, allowing life to break away from the vents on at least two occasions – one giving rise to the first archaea, the other to bacteria.