Last universal common ancestor

All living things on the planet have a common genetic heritage. Humans, for example, share more than 99% of the genome with chimpanzees, but also half with bananas. This has allowed experts to deduce that life on Earth had the same origin and that there must be a single ancestor of all the organisms that inhabit it, from bacteria to blue whales. This universal ancestor is known as LUCA, an acronym for Last Universal Common Ancestor. Researchers think it may have emerged in environments similar to geysers and geothermal sources in Yellowstone Park in the United States (photo).

As its name suggests, it is the last ancestor common to all life forms, but it does not represent the earliest stage of evolution. In fact, what happened before him is something we still don't know very well. On the other hand, the fact that all living beings share the same genetic code tells us nothing about the nature of LUCA.

What traits are common to all cellular life? To determine this, perhaps we should compare the representative genomes of the three natural domains: archaea, bacteria and eukaryotes. Genes that are common to all of them would also have been present in LUCA.

This is easier said than done. One problem is that genes move from one organism to another, in a process called horizontal transfer. For example, 100 million years ago the bacterium Escherichia coli acquired at least 10% of the genome through more than 200 such events.

It may also happen that certain genes found in LUCA are no longer universal, that is, they disappear from some domain. Some scientists argue that such transfer is so important that, in practice, it is impossible to build evolutionary trees -something like genealogies-, while others think such a phenomenon is insignificant.