Features of how DNA, RNA, and proteins are built and metabolized are common to every living thing we’ve looked at, suggesting they were inherited through common descent. While life may have arisen more than once, it appears that only one lineage has survived down to the present day.

If you could trace living lineages back far enough, you’d arrive at an organism that’s the ancestor to every living thing: the last universal common ancestor, or LUCA. This idea has naturally led to a lot of speculation about what LUCA might have looked like. In the latest effort to offer some informed opinion, scientists have performed a clever genomic analysis to identify some of the genes that were probably in LUCA. Those genes, in turn, allow us to infer something about how LUCA lived and what environments it inhabited.

Building trees

Various analyses have indicated that organisms with complex cells (eukaryotes) are a relatively recent development on Earth—assuming you’re willing to call something over two billion years old “recent.” Two other lineages, bacteria and archaea, go back much further. LUCA sits at the point where bacteria and archaea started to diverge. So if you can identify genes that have been inherited by both of these lineages, they probably were present in LUCA’s genome as well.