Would humans die without clothes? Yes. That is the entire answer, and the reason is written across 3 million years of evolution.
The seed was planted 30 million years ago. Plate tectonics tore Antarctica away from Australia, raising permanent ice sheets; the Tibetan Plateau rose toward 3,000 meters; the East African Rift split open for 6,500 kilometers. East and North Africa turned extreme — year-round drought, bitter winter cold, brutal summer heat and ultraviolet — and stable forests fragmented and vanished. Our last ancestors with monkeys were forced out of the trees they could no longer keep: they lost the forest niche to monkeys, the forest-edge niche to chimpanzees' ancestors, and walked out into the dry grassland.
Then came the Quaternary glaciation, beginning 2.58 million years ago — one of the coldest valleys the planet has seen in 500 million years, cycling between glacial and interglacial periods every 41,000 years at first, later every 100,000 years.
The killer upgrade: throwing.
A 2013 Nature paper explained how our ancestors became "the terrifying upright ape." Chimpanzees can throw, but badly — an adult male chimp's explosive power exceeds a human man's, yet its throwing speed is only half that of an eight-year-old child, with accuracy best described as random. Our ancestors rebuilt their bodies for throwing: broad shoulders, long legs, flexible wrists, and a shoulder-arm structure that stores and releases elastic energy from the hips and waist. Fast, stable, sustained throwing flipped the food chain, and there was no predator left.
Then the heat problem forced us to take off our fur.
Persistence running at full tilt produces around 1,000 W of heat — ten times resting output. Picture a 1,000 W space heater set to 37 °C running for one or two hours straight inside a room. The earliest endurance runners literally died of heatstroke — until, among them, there were always a few mutants with reduced hair and well-developed sweat glands that could shed heat by sweating. They survived, and because they ran farther, they caught more prey and multiplied. Their genes took over. And since hunting provided animal hides, the loss of fur never threatened survival — it was just inconvenient without coverage.
Lice dated our clothes, and our naked skin.
Human body lice evolved from head lice about one million years ago — which means our ancestors were already wearing clothes back then. Head lice, in turn, trace back to gorilla lice around 3.3 million years ago, hinting that hair loss happened somewhere between 1 and 3 million years ago. (An older hypothesis blames parasite pressure for stripping our fur; either way, the timeline holds.) The ice-age cycles then made clothing compulsory: any hominin that refused to cover up froze out of the gene pool.
Around 1.7 million years ago, the Acheulean tool industry arrived — hand axes, picks, and cleavers with precisely worked edges — and with it the ability to mass-produce clothing from animal hides and even plant materials. Clothing spread because it kept people alive.
The bottlenecks: humanity nearly went extinct, more than once.
Between 930,000 and 813,000 years ago, the ancestors of Homo sapiens crashed to a breeding population of about 1,280 individuals — one-fourteenth of the previous 18,000. The usual extinction floor is thought to be around 500 breeding individuals. They survived, barely. Then, around 70,000 years ago, the final bottleneck: the effective breeding population fell to about 2,000 — some local groups as low as 150. The Toba eruption was long blamed; newer work shows it was smaller than thought, though its volcanic winter still lasted nearly a decade and cooled the climate for a millennium.
Why 1,700 ml of Neanderthal brain lost.
