Science Focus
original post »Eukaryotes—fungi, plants, us—are complex. Our large cells are characterized by their different compartments, many of which are neatly enclosed within a boundary of membrane. These compartments contain complex molecular machines that perform equally complex metabolic tasks: they degrade proteins, they splice RNA molecules, they engulf foreign bodies.
Prokaryotes, on the other hand—one celled organisms like bacteria—are simple, with a notable lack of internal membrane enclosed structures (i.e., nuclei) in their one and only cell. It has been assumed that eukaryotes must have somehow evolved from prokaryotes, but it has not been at all clear how that may have happened.
A clue came in 1977, when another branch type of prokaryotic life was discovered: archaea. They are single-celled organisms that lack nuclei and other structures, just like bacteria. But from an evolutionary standpoint, they are about as distant from bacteria as they are from eukaryotes. As soon as archaea were recognized, people started speculating that eukaryotes may have originated within the archaeal branch of life rather than the bacterial branch, or that eukaryotes and archaea might share a common ancestor.
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