(...) One major complication: Microbes not only pass genes to their progeny, but also swap them among their neighbors in a process called horizontal gene transfer. This makes it hard to tell whether genes shared by separate microbes reflect a shared lineage or whether some bugs were just better at spreading their genetic material far and wide. And that makes it harder to pin down LUCA’s lifestyle.
To get closer to doing just that, researchers led by William Martin, an evolutionary biologist at Heinrich Heine University in Dusseldorf, Germany, took a more stringent approach to identifying genes that were likely inherited. Rather than looking for genes shared by a single species bacteria and archaea, they searched for those shared by at least two species of bacteria and two archaea. (...)