Anthropology & Human Origins

Recent Discoveries Have Overhauled Where — and When — Humans Came From

The story we learned in school — Homo sapiens evolved in Africa, walked out, and replaced everyone else — is getting messier by the year. A cluster of recent findings is forcing a more tangled, more interesting picture of human origins.

• A small-brained hominin, Homo naledi, buried bodies in a deep South African cave around 300,000 years ago — behaviour once thought unique to our own species.
• Genetic evidence keeps revealing that the ancestors of living humans interbred with several now-extinct cousins, including the Denisovans, whose DNA still lives in people across Asia and Oceania today.
• Human occupation of continents we thought was reached much later keeps getting pushed forward by new archaeological dates.

The star of this revision is Homo naledi, a species announced in 2015 after fossils from 15 bodies were recovered from a chamber so deep and narrow inside the Rising Star cave system that only slender researchers could reach it. H. naledi had a brain the size of an orange — about 450 cubic centimetres, roughly a third of a modern human brain — yet placed its dead in a hard-to-reach chamber. Reaching the chamber requires a squeezing crawl down a fissure, then a climb up a vertical shaft; the bodies show no sign of being washed in by water or dragged by predators. Deliberate placement is the best explanation scientists have, and it implies a capacity for symbolic or ritual behaviour in a species we assumed was too primitive for it.

Genetics has delivered an even deeper revision. Sequencing of ancient DNA has shown that the line leading to modern humans did not simply march forward. As H. sapiens spread from Africa, they met and mated with archaic populations — Neanderthals in Europe and western Asia, and Denisovans in Asia. A small percentage of Neanderthal DNA survives in most non-African populations today, while Denisovan DNA reaches up to 5 percent in some Island Southeast Asian and Melanesian groups. We are not a pure lineage; we are a hybrid of several.

The lesson, as palaeoanthropologists put it, is that the "single story" model no longer fits the evidence. The human family tree is more of a braided stream: lineages that appeared separate in the fossil record were mingling, going extinct, and shaping each other in ways we are only beginning to see.