W.W. NORTON & COMPANY, JULY 2015There's a black hole at the heart of biology. Why is it that complex eukaryotic cells share so many fundamental traits, from the nucleus to meiotic sex, which are essentially absent from prokaryotes? Most people would be hard pressed to distinguish a human cell from those of a mushroom, a plant, or a zoospore. Yet those cells diverged a billion years ago, and have utterly different ways of life.
Genes point to an answer, but don't explain the whole story. All eukaryotes share a common ancestor that arose just once in four billion years of evolution. This ancestor was recognizably a modern eukaryotic cell, with a long list of characteristics inherited by its varied descendants, including straight chromosomes, introns and exons, nuclear pore complexes, dynamic cytoskeleton, endomembranes, sex, and mitochondria.
Phylogenetics also point to a chimeric origin of eukaryotes. Long before that common ancestor, an archaeal host cell somehow picked up a population of intracellular bacteria that ultimately evolved into mitochondria. The identity of that host cell and the process by which it acquired mitochondria is controversial. The recent discovery of Lokiarchaeota, which branch close to modern eukaryotes, corroborates the archaeal ancestry of the ...
