The latest chapter of human evolution begins with the emergence of Homo sapiens. The anatomy of Homo sapiens is unique among hominin species and appears first in East Africa, dating to roughly 160 thousand years ago (ka). These unique features—including changes in the skull and postcranial skeleton (skeleton minus skull)—suggest changes in brain size and architecture and an adaptation to tropical environments. These anatomical changes are linked to cognitive and behavioral changes that are equally unique among hominin species. In particular, the archaeological evidence of behaviors thought to be unique to Homo sapiens, which appear first in Africa around 170 ka, highlight the importance of symbolism, complex cognitive behaviors, and a broad subsistence strategy (the strategy used to procure food). The evolution of Homo sapiens is vitally important to defining our species in the broader context of human evolution and also has key to understanding the human condition, past and present.
Many of the unique features of Homo sapiens are found in the skull. Brain size estimates suggest that the brain of Homo sapiens was larger than in other hominin species. The average cranial capacity of Homo sapiens is roughly 1300 cubic centimeters, making the brains of this species absolutely smaller than those of Homo neanderthalensis. However, due to its gracile (small and lightly built) postcranial skeleton (see below), the brain of H. sapiens was larger relative to body size than that of H. neanderthalensis. The skull itself is much taller than earlier hominin species and the skull is therefore much shorter (from front to back) in relation to its height. The widest point of the Homo sapiens skull is toward the top of the skull and the sides of the skull are nearly vertical. Together with the extreme height of the skull, these features give the Homo sapiens skull a house-shaped (i.e., pentagon with straight walls) appearance when viewed from behind. The skull of Homo sapiens also generally lacks evidence of being strongly built (e.g., it lacks the large browridges and bony prominences seen in Homo neanderthalensis and Homo heidelbergensis). However, the earliest representatives of the species maintain a fairly rugged appearance. For instance, the browridges of early H. sapiens are fairly large, but differ in shape from those of H. neanderthalensis and H. heidelbergensis. The face of Homo sapiens is much smaller than those of earlier hominin species. In addition the face is “tucked under” the braincase—i.e., the face is located entirely below (rather than in front of) the front part of the brain. The face of this species also bears a deep indentation (the canine fossa) below each of the orbits. The teeth and mandible (lower jaw) are smaller than in earlier species and the mandible bears a prominent mental prominence (chin), which is not seen in any other hominin species.