Compared to H. erectus, H. sapiens, or humans, have larger brains and different faces, and they mature slower, reproduce faster, and carry more fat. Compared to most mammals, humans produce fewer offspring with higher survival rates. Humans take 18 years to mature, and human mothers reproduce twice as often as apes and can care of more than one dependent offspring at a time.

H. erectus dispersed from Africa to Europe and Asia. Researchers hypothesize that H. erectus lived in small bands inhabiting large territories and that their populations increased relatively rapidly. Lieberman notes it’s strange that H. erectus dispersed into temperate regions in the Ice Age, given the extreme low cyclical temperatures.

Dispersed groups become isolated, and isolated groups are subject to unique natural selection. H. erectus groups varied in size and evolved into distinct species of archaic Homo including H. heidelbergensis, the Denisovans, and Neanderthals. Genetic research shows humans interbred sparsely with the Denisovans and Neanderthals. These archaic Homo had larger brains, lived as hunter-gatherers, made advanced tools, and learned to control fire.

Neanderthals diverged from modern humans up to 800,000 years ago. They lived in Europe and Asia up until 30,000 years ago, and they were intelligent hunter-gatherers adept at surviving in cold environments.