Symbiosis | Kaelan

Lynn Margulis championed endosymbiosis: the theory that mitochondria and chloroplasts were once free-living bacteria that merged with ancestral cells. The evidence is overwhelming — they have their own DNA, their own ribosomes, double membranes consistent with engulfment. The cells that power all complex life arose through cooperation, not competition.

This wasn’t a minor event. The merger gave eukaryotes vastly more energy per gene, enabling larger genomes, more complexity, eventually multicellularity. Every plant, animal, and fungus descends from that ancient partnership. Evolution’s greatest innovations came not from competition but from merger.

Symbiosis pervades biology. Coral reefs exist because coral animals host photosynthetic algae. Legumes fix nitrogen through bacterial partners in root nodules. Your gut contains trillions of bacteria that digest food, synthesize vitamins, train your immune system. You are not an individual organism — you are an ecosystem.

The implications for understanding evolution: competition is only half the story. selection acts on cooperative assemblages, not just isolated individuals. A lichen is neither fungus nor alga but their partnership. A termite cannot digest wood without its gut symbionts. The unit of selection is often the relationship, not the organism.

Mutualism evolves when cooperation pays — when two species can do together what neither can do alone. The relationship can be obligate (neither survives without the other) or facultative (both benefit but can survive apart). Pollination networks, seed dispersal, cleaning symbioses: nature is woven from mutual dependencies.

The pattern extends beyond biology. Economies run on specialization and trade — each party providing what the other lacks. Cities concentrate complementary skills. scenius emerges when creative people feed each other’s work. Competition grabs attention, but cooperation builds complexity.