Our species, Homo sapiens, is the only living species in the Homo genus. (Present-day man is actually a member of subspecies sapiens--total name Homo sapiens sapiens--but we share all features with the main species). Homo sapiens are characterized by bipedal posture, excellent eyesight, and a very large brain that allows for innovative thought and problem-solving capabilities. The head of a Homo sapiens is larger than other primates because the skull needs room to enclose this large brain. Humans also have a highly developed nervous system and strong senses. Especially important is depth perception (stereoscopic vision), made possible because their eyes are located near each other. Like other apes, humans have opposable thumbs and nails on their fingers, but they lack tails. The upper legs of a human have very strong muscles allowing it to stand upright. A curve in the spine near the lower back also allows upright posture because the center of gravity of a human is directly over the pelvis.

Humans probably evolved from Australopithecus afarensis because this was the first species to stand upright. However, afarensis did not have a large brain comparable to the brain of a human. This species died out by about 1.4 million years ago, but probably gave rise to the Homo genus. The first species of this genus was Homo habilis (handy man), first seen about 2.5 million years ago. This species was upright and had a much larger brain than afarensis. Homo habilis was probably able to use simple tools and lived a hunting/gathering lifestyle. This species gave rise to Homo erectus (upright man), first seen 1.8 million years ago. These "people" were larger than Homo habilis and had an even larger brain. They were even able to develop some civilization, living in groups and making permanent settlements. Homo erectus died out about 250,000 years ago, but not before giving rise to our species, Homo sapiens. Humans were first seen 300,000 years ago. Homo sapiens had thicker bones, a larger brain, and pronounced brow ridges. While some scientists believe that this species originated in Africa, others pose that simultaneous evolution in many places created a species that developed in many places at once. The oldest fossils of modern Homo sapiens were found 100,000 years ago, a period when Homo sapiens first covered the Old World. These Homo sapiens were hunter/gathers and scavengers. However, about 5,000 years ago, farming was begun, and people were able to settle down, raise crops, and domesticate animals. Once humans were settled, civilization took hold, first in Mesopotamia but soon in Egypt and elsewhere. Evolution has continued, and tools have improved, but the people today are fundamentally similar with Homo sapiens throughout time.