Traditionally, scientists used the term "hominid" to describe the species in the human lineage (species that evolved after the split between modern humans and the great apes of Africa). The main trait for defining a species as "hominid" was bipedality (walking on two legs). This had evolved by about 4 million years ago. In a sense, if a primate walked on two legs, it was a hominid. However, more recent genetic evidence has suggested a different classification. Recall that geneticists' experiments have shown that humans are probably more closely related to the chimpanzees than to the other apes (for example, the gorilla). So a traditional classification that puts gorillas and chimps together in one group, and humans and other hominids in a different group, doesn't accurately reflect the evolutionary relationships between these species.

So a new classification is being adopted by a growing number of researchers. In this new system, the family Hominidae, or "hominids," is now considered to include all of the great apes (chimps, humans, gorillas, the Asian orangutan, as well as all the extinct species in the fossil record related to these species). A subfamily Homininae (the "hominines") is used to refer specifically to the African apes; chimps gorillas and humans, which separated evolutionarily from the Asian apes around 13 million years ago. Orangutans, and their extinct relatives are placed in the subfamily Ponginae (the "pongines"). To characterize the human line after its split from the other African ape lineages between 5 and 8 million years ago, a tribe classification Hominini ("hominins") is adopted.

But it isn't that simple! Some researchers strongly disagree, preferring the traditional classification, and they reserve the term hominid strictly for the human lineage. Still others argue that the creation of a tribe classification is not warranted. Other researchers place the orangutans in a separate family Pongidae, instead of separating them at the subfamily level . . .

Confused yet?