Humans (Homo sapiens) are the most abundant and widespread species of primates, characterized by bipedality and large, complex brains enabling the development of advanced tools, culture and language.

The first fossil skulls of Homo erectus, 1.8 million years ago, had brains averaging a bit larger than 600 ml. From here the species embarked on a slow upward march, reaching more than 1,000 ml by 500,000 years ago. Early Homo sapiens had brains within the range of people today, averaging 1,200 ml or more.