All living things on earth are related to each other. Now a research team has counted backwards in evolution and has been able to reconstruct an organism from which all other organisms are descended. It is called LUCA, after the English Last Universal Common Ancestor. It lived 4.2 billion years ago, just a few hundred million years after the Earth formed, and got its energy from hydrogen and carbon dioxide, which were abundant at the time.
So it survived
LUCA has a genome that codes for about 2,600 proteins, which means it resembles a bacterium. In addition, the genes reveal what characteristics the organism had in order to survive on the very young Earth. The research is published in Nature Ecology & Evolution.
Ulf Ellervik, professor of organic chemistry at Lund University, has read the study and thinks it is robust.
– I think it is exciting that genes have been found that provide UV protection. It could mean that it has been exposed to the sun’s UV radiation, he says.
Near the water surface
This in turn means that LUCA may have lived near the surface of the water and therefore needed to develop protection against the sun’s radiation. It therefore did not live near hot springs on the sea floor, where many suspect that life first took root.
So much suggests that LUCA was not the very first life on Earth.
– We were very surprised when we found a collection of proteins called Crispr Cas. We didn’t expect that at all, says Edmund Moody at the University of Bristol, who led the study.
Crispr cas is part of the bacteria’s DNA that makes up their immune system. So our oldest common ancestor had thus built up defenses against others, perhaps viruses or other organisms of which there are no longer any traces.