Symbiogenesis
All life came from the sea, and the interior of every cell in every living organism reproduces that salty, watery environment—a tiny “ocean inside.” This much is common knowledge. But our mitochondria, the “power plants” within our cells where respiration takes place, may in fact be recapitulating the much more specific deep-sea chemistry of a black smoker. In an almost literal sense, our bodies are like Russian matryoshka dolls, membranes within membranes, and each nested environment recreates an earlier stage in the evolution of life on Earth.
The deeper inside ourselves we look, the farther we can see into the past. A beautiful, shivery thought.
The idea that evolution is driven by symbiotic mergers, the earliest of which preceded biology as we know it, has far-reaching implications. One is that the boundary between life and non-life is not well defined; symbiogenesis can involve any process that, one way or another, is self-perpetuating. Evolutionary dynamics are thus more like a physical law than a biological principle. Everything is subject to evolution, whether we consider it to be “alive” or not.
The symbiogenetic view also renders the idea of distinct species, classified according to a Linnaean taxonomy, somewhat ill-defined—or at best, of limited applicability.
When one prokaryote ends up living inside another, though, or multiple cells band together to make a multicellular life form, the resulting composite organism is clearly more complex than its parts. Something genuinely new has arisen. The branching and fine-tuning of classical evolution can now start to operate on a whole different level, over a new space of combinatorial possibilities.
Classical evolution isn’t wrong; it just misses half of the story—the more rapid, more creative half. One could say that evolution’s other half is _revolution, and that revolutions occur through symbiosis.
It’s equally meaningful to talk about ancient life forms, like bacteria and archaea, co-existing alongside recent and far more complex ones, like humans—while recognizing that humans are, in a sense, complex colonies of bacteria and archaea that have undergone a cascade of symbiotic mergers.