A hominin is any member of the taxonomic tribe Hominini, which consists of all humans and their extinct bipedal relatives dating back to the last common ancestor of Homo and Pan. The term “hominin” is derived from the Latin word “homo”, meaning “man”, and the suffix “-in” which denotes membership in a group. The tribe Hominini includes two subdivisions: the subtribe Hominina, consisting of only modern humans; and the subtribe Australopithecina, consisting of both extinct australopithecines and extant gorillas and chimpanzees.
The split between these two groups occurred about 8 million years ago, with the earliest fossils belonging to the australopithecines dating back to around 5 million years ago. The first hominins were small-bodied creatures that resembled apes in many ways, but had some key anatomical differences that set them apart. For example, they had longer legs relative to their bodies than apes do, indicating that they were more efficient at walking long distances on two legs. They also had enlarged brains compared to other apes, although not as large as those of modern humans.
The first members of the genus Homo appeared around 2 million years ago and included early human species such as Homo habilis and Homo erectus. These species were more similar to modern humans than earlier hominins, with larger brains and bodies adapted for walking upright on two legs over long distances. The last common ancestor of all living humans (Homo sapiens) lived around 300,000 years ago, while our direct ancestors (the Neanderthals) diverged from this lineage around 600,000 years ago.
There are a number of different theories about why our ancestors began to walk upright on two legs instead of four. One theory suggests that it was an adaptation for moving through open grasslands where trees were sparse; another argues that it was an evolutionary advantage for hunting or scavenging on African savannas; while a third proposes that it simply made it easier to carry resources such as food or water over long distances. Regardless of the reason why our ancestors began walking upright, this change in locomotion led to a number of other changes in anatomy and physiology that helped make us uniquely human. For example, because we no longer needed grasping hands for climbing trees, our fingers became shorter and less agile; likewise, because we spent less time in trees overall, our bones became thinner and less robust (a trait known as gracilization). Walking upright also freed up our arms so that we could use them for carrying objects or tools; this eventually led to the development of manual dexterity which allowed us to create complex technologies like spears or arrows