Humans (Homo sapiens, meaning "thinking man" or "wise man") are the most common and widespread species of primate, and the only extant species of the genus Homo. They are great apes characterized by hairlessness, obligate bipedality, manual dexterity with opposable thumbs, precision grip, and high intelligence. Humans have large brains compared to body size (a high encephalization quotient), enabling more advanced cognitive skills that facilitate successful adaptation to varied environments, development of sophisticated tools, and formation of complex social structures and civilizations. Humans possess a disproportionately larger volume of both cerebral white matter and gray matter present in the prefrontal cortex (PFC) than any other primate species, which facilitated the expansion of higher-order executive functions. Humans are highly social, with individual humans tending to belong to a multi-layered network of distinct social groups – from families and peer groups to corporations and political states. As such, social interactions between humans have established a wide variety of values, social norms, languages, and traditions (collectively termed institutions), each of which bolsters human society. Humans are also highly curious: the desire to understand and influence phenomena has motivated humanity's development of science, technology, philosophy, mythology, religion, and other frameworks of knowledge; humans also study themselves through such domains as anthropology, social science, history, psychology, and medicine. On November 15, 2022, the 'Day of Eight Billion' marked a demographic milestone; as of 2026, there are estimated to be more than 8 billion living humans (≈ 8.3 billion). For most of their history, humans were nomadic hunter-gatherers. Humans began exhibiting behavioral modernity about 160,000–60,000 years ago.