What the analysis actually claims

In Düsseldorf, Natalia Mrnjavac and colleagues from William Martin's group examined the 420 chemical reactions that basic metabolism requires and the structures of the proteins that run them. Their conclusion is that the bacterial and archaeal lineages acquired about half their enzyme genes independently, after parting from the last universal common ancestor of everything alive, placed at roughly 4.2 billion years ago. The study appeared in Science Advances.[1]

The reasoning runs like this. Where the enzymes running the same reaction turn out to be unrelated in the two lineages, that enzyme is taken to have arrived after the split. Martin says the approach opens a view onto the phase of evolution in which very primitive proto-organisms were inventing enzymes. Mrnjavac says the two lineages traversed the path to free-living cells at least in part independently.[1]

What it leaves standing

There is a boundary here that asks for care. Betül Kaçar, who works at NASA's astrobiology centre and the University of Wisconsin–Madison, points out that the last common ancestor is not the same thing as the origin of life, and says that how chemistry and geology passed the baton to biology remains unknown. The study therefore describes what happened when a cell already existed, rather than how that cell came to exist.[1]

One more reading fits the same data. The two lineages could have inherited their enzymes from the common ancestor and later replaced some of them independently. In structural comparisons that would also produce enzymes showing no kinship. Separating invention from replacement is the hard part, and until that separation is made the proportion should be read as an upper bound.[1]

Why this carries beyond the laboratory

What stands out is how small the number is. Basic metabolism asks for 420 reactions, few enough to be written as a list. Our intuition about the beginning of life usually leans on a picture of impossible complexity, whereas in this frame the first cell reads as a stage rather than a finish line: a chemistry that works, has gaps, and is still being written.[1]

The place where this gets tested is the bench rather than the desk. If one of those 420 reactions is shown in the laboratory to run without an enzyme under conditions like those of a hydrothermal vent, the claim stops being a proposal about ordering and attaches to chemistry. It is a signal worth waiting for, because once it is shown, the gap before that cell narrows a little.[1]