Humans are classified as anthropoids, a scientific grouping within the Order Primates known as the higher primates. The Order Primates includes species ranging from tiny mouse lemurs to the great apes. The term “anthropoid” corresponds to the infraorder Simiiformes, a major branch in the primate evolutionary tree. This classification links our species, Homo sapiens, to all other monkeys and apes, confirming our membership based on defining anatomical and genetic traits.
Understanding the Primate Family Tree
The Order Primates is divided into two distinct suborders. These are the Strepsirrhini, or “wet-nosed” primates, and the Haplorhini, or “dry-nosed” primates; humans belong to the latter group. Strepsirrhines include species like the lemurs and lorises, which generally retain more ancestral traits, such as a moist nose pad and a greater reliance on the sense of smell.
The Haplorhini suborder is then separated into two infraorders: the Tarsiiformes, which contains the small, nocturnal tarsiers, and the Simiiformes. It is this Simiiformes infraorder that is scientifically synonymous with the common term Anthropoidea. Anthropoids encompass all monkeys and apes, including our own species.
Defining Features of Anthropoids
Anthropoids possess a suite of derived physical characteristics that distinguish them from the other primates, particularly the Strepsirrhines. A major evolutionary trend in this group is the significant increase in relative brain size and complexity, supporting more intricate social behaviors and problem-solving abilities. This neurological development is coupled with a pronounced shift in sensory reliance from olfaction to vision.
Anthropoids exhibit superior stereoscopic vision, with fully forward-facing eyes that allow for excellent depth perception. The eyes are fully protected by a bony structure called post-orbital closure, a feature absent in Strepsirrhines. Most anthropoids are diurnal, or active during the day, which led to the evolution of superior color vision. They also tend to have longer gestation periods and greater parental investment in their offspring.
The Human Lineage Within Anthropoids
The Anthropoidea infraorder (Simiiformes) is further categorized into two parvorders, based primarily on geographic distribution and nasal structure. These are the Platyrrhini, or New World monkeys of Central and South America, and the Catarrhini, or Old World monkeys and apes of Africa and Asia. Humans belong to the Catarrhini, sharing the characteristic downward-pointing nostrils and a dental formula different from the Platyrrhines.
The Catarrhini parvorder is then split into two superfamilies: the Cercopithecoidea (Old World monkeys, such as baboons and macaques) and the Hominoidea, which represents all apes. The Hominoidea superfamily includes two families: the Hylobatidae (gibbons, or lesser apes) and the Hominidae, or the great apes. The Hominidae family includes the orangutans, gorillas, chimpanzees, and humans, confirming the human classification as a great ape.
Within the Hominidae family, humans belong to the tribe Hominini, and members of this tribe are referred to as hominins. This final classification includes modern humans, Homo sapiens, and all extinct bipedal ancestors since the split from the chimpanzee lineage.