Abstract

Chemiosmotic coupling is as universal as the genetic code, yet its origins are poorly understood. I will show how natural proton gradients could have driven the emergence of cells in hydrothermal vents. Prokaryotes are then constrained by membrane bioenergetics. Despite their biochemical virtuosity, neither bacteria nor archaea show any tendency to evolve complex eukaryotic traits or large genomes. All complex life on Earth is eukaryotic, and all eukaryotes share a common ancestor that was already a complex cell, with a nucleus, dynamic cytoskeleton, meiotic sex, etc. Eukaryotes arose in a rare endosymbiosis between two prokaryotes, which broke the energetic constraints on prokaryotes through the evolution of mitochondria. Loss of almost all mitochondrial genes produced an extreme genomic asymmetry, in which tiny mitochondrial genomes support, energetically, a massive nuclear genome, giving eukaryotes 3-5 orders of magnitude more energy per gene than prokaryotes. The requirement for endosymbiosis radically altered selection on eukaryotes, potentially explaining the evolution of deeply conserved traits including two sexes, germline, apoptosis, speciation, ageing and disease.