HUMAN EVOLUTION × GENETICS

The First of Our Own Branch

~7 million years ago

Phanerozoic · Cenozoic · Neogene · Miocene

A crushed skull and a few limb bones from Chad, belonging to an ape that seems to have walked upright. The hole where the spine enters the skull sits forward, as it does in us and not in a chimpanzee, and a thigh bone from the same locality points the same way. Two arm bones described with it say something else: this animal still climbed, and climbed a lot. Its age, about seven million years, is close to the genetic estimate of our split from chimpanzees.

Why it matters

The parting of two lineages is not the clean break the phrase suggests. Nothing here abandoned the trees to walk. Walking and climbing were the work of one animal, and stayed that way for millions of years, so bipedalism was added to a life in the branches rather than exchanged for it.

Dating & uncertaintyDisputed

Sahelanthropus at about 7 Ma and Orrorin at about 6 Ma are both claimed as hominins on fragmentary remains, and both claims are contested. Genetic estimates of the split from chimpanzees range from roughly 6 to 9 Ma depending on the generation time assumed.

Sources

1. Brunet et al. (2002), Nature · A new hominid from the Upper Miocene of Chad, Central Africa
2. Daver et al. (2022), Nature · Postcranial evidence of late Miocene hominin bipedalism in Chad
3. Langergraber et al. (2012), PNAS · Generation times in wild chimpanzees and gorillas suggest earlier divergence times in great ape and human evolution

Earth history as one day

23:57:462 min 13 s before midnight

if Earth’s 4.54 billion years were compressed into a single day