Who Was Our Very Oldest Ancestor?

The extreme life of LUCA.

Scientists have learned new details about the life of our last universal common ancestor (LUCA) — the ancestor that gave rise to humans, monkeys, fish, flowers, and bacteria. By mining the genes of nearly 2,000 of its modern microbial descendants, researchers have identified 355 genes that this oldest ancestor probably possessed.

“It was flabbergasting to us that we found as many as we did,” William Martin of the University of Dusseldorf in Germany, who led the Nature Microbiology study, tells New Scientist.

The genes suggest that these organisms, which lived nearly four billion years ago, inhabited an oxygen-free world. Carbon dioxide and nitrogen would have been available as raw materials for building their cellular structures, and their energy came from hydrogen gas, which they would have acquired from the hydrothermal vents where they most likely lurked. LUCA also had an enzyme that would have allowed it to flourish in extremely high temperatures.

SEE ALSO: How Did Life Begin?

Even today, hydrothermal vents are breeding grounds for extreme organisms, and scientists have long theorized the first life forms arose in these environments. Many of the newly identified LUCA genes bolster this theory.

One challenge the researchers encountered was figuring out which genes present in the microbes that they studied were passed down from LUCA, and which were acquired from other modern-day organisms through a process known as horizontal gene transfer. But by focusing on snippets of DNA that were present in at least two species of bacteria and two archaea, they could rest assured that these sequences were unlikely to have been acquired multiple times via horizontal gene transfer.

This research provides the most complete picture to date of the single cell from which all life on Earth descended aka, our great-great-great-great-great (etc.) grandparent.

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