What if a critical determinant of human physiology began as an ancient bacterial infection that never ended?
Approximately 2 billion years ago, an ancestral eukaryotic cell internalized an aerobic α-proteobacterium, giving rise to the mitochondrion via endosymbiosis.
Today, mitochondria are central to oxidative phosphorylation, generating the majority of cellular ATP and regulating apoptosis, calcium homeostasis, and reactive oxygen species (ROS) signaling — processes fundamental to tissue function and disease.
Their retained circular mtDNA, 70S ribosomes, and binary fission continue to reflect their prokaryotic ancestry. Clinically, mitochondrial dysfunction is implicated in neuromuscular disorders, metabolic syndromes, aging, and ischemia-reperfusion injury, underscoring their relevance beyond energy production. Human health depends on organelles that are evolutionary remnants of ancient bacteria.