Biologists split life into two broad categories: prokaryotes and eukaryotes. Prokaryotes are relatively simple single-celled organisms and are split into two groups (bacteria and archaea). Eukaryotes, on the other hand, are much more complex cells containing specialized compartments such as the nucleus, mitochondria, and other membrane-bound organelles. All of what we consider complex life (e.g. plants, animals, fungi, protists) are eukaryotes. Scientists have long been interested in determining how eukarotes evolved from prokaryotes. This week, researchers published the discovered a new species of archaea which shares many features with eukaryotes and is the closes known prokaryotic relative of all eukaryotes. The finding explains the evolutionary origins of many features once thought to be unique to eukaryotes, and strengthens the "two-domain" hypothesis of life: Sprang et al. 2015 Complex archaea that bridge the gap between prokaryotes and eukaryotes Nature. Published online 06 May 2015. http://dx.doi.org/10.1038/nature14447 [Broken] See also this summary from National Geographic: http://phenomena.nationalgeographic...robe-is-closest-relative-to-all-complex-life/ Although this finding answers many questions about the evolution of eukaryotes, more work remains to be done to understand the evolution other features unique to eukaryotes, such as the evolution of the nucelus. However, because eukaryotes evolved from these "Loki" archaea after they endosymbioticallly captured an alphaproteobacterium, it would be a neat experiment to try to recreate this event in the lab.