If you're a fan of articles like this, you owe it to yourself to read The Vital Question by Nick Lane. He's a British biochemist working at University College L

If you're a fan of articles like this, you owe it to yourself to read The Vital Question by Nick Lane. He's a British biochemist working at University College London and the book offers a detailed hypothetical route to the eukaryotic endosymbiosis. The genetic and energetic evidence he provides is compelling. In 2015 he apparently commented on Ettema's research [1] mentioned in OP: Ettema’s team argue that their finding helps bridge the gap between our cells and those of the typical prokaryotic organisms from which we are believed to have evolved. Others are more sceptical. “We’re getting closer to an archaeal ancestor of the eukaryotes,” says Nick Lane of University College London. However, even though the Lokiarchaea are relatively complex compared with other known archaea, they lack the large genome and energy-producing mitochondria of true eukaryotic cells. “It’s a thousandth of the way towards the complexity of a eukaryote,” says Lane. So we can’t really call them an intermediate step or a missing link. Lane believes the crucial step in the evolution of the eukaryotes was acquiring mitochondria, which would have provided the energy to develop more complicated cellular processes and acquire a larger genome. Ettema does not think the Lokiarchaea have mitochondria, but he says some form of intracellular transport may have evolved before our ancestors acquired their powerhouses. [1] https://www.newscientist.com/article/mg22630204-000-microbes-found-at-bottom-of-ocean-are-our-long-lost-relatives/ https://www.newscientist.com/article/mg22630204-000-microbes...