Hominini

The tribe Hominini, whose members are called hominins, sits within the subfamily Homininae. It includes two living genera: *Homo* (humans) and *Pan* (chimpanzees and bonobos). Under the standard arrangement, gorillas are left out, placed instead in their own tribe, Gorillini, still within Homininae. The name Hominini was first proposed by Camille Arambourg in 1948, who merged the categories Hominina and Simiina based on Gray’s classifications from 1825.

Traditionally, chimpanzees, gorillas, and orangutans were lumped together as pongids, with humans excluded. But as genetic evidence piled up, it became clear that humans, chimpanzees, and gorillas are more closely related to one another than any of them is to orangutans. So orangutans were moved into the family Hominidae (the great apes), which already held humans, and gorillas were given their own tribe, Gorillini, within Homininae. Even so, the details of this reshuffling are still debated, and not every source agrees: some include gorillas in Hominini, others leave chimpanzees out.

Humans are the only living species in the Australopithecine branch (a subtribe), which also contains many extinct close relatives.

**Terminology and definition**

If Hominini is defined to exclude *Pan*, then the tribe Panini (or “panins”) can be used for chimpanzees alone. Alternatively, *Pan* might be grouped with other dryopithecine genera, making the whole group Panini or Panina. A few minority views put *Gorilla* inside Hominini, or even place both *Pan* and *Gorilla* within *Homo* (Goodman et al. 1998; Watson et al. 2001).

By convention, the adjective “hominin” (or the noun “hominins”) refers to the tribe Hominini, while members of the subtribe Hominina—that is, all archaic human species—are called “homininan” or “homininans.” This follows Mann and Weiss (1996), who proposed that Hominini includes both *Pan* and *Homo*, each in its own subtribe: *Pan* in Panina, *Homo* in Hominina.

An alternative convention uses “hominin” to exclude Panina, applying it only to *Homo* or to human and australopithecine species. This is seen in Coyne (2009) and Dunbar (2014). Potts (2010) goes further, using Hominini in a sense that excludes *Pan*, and introduces a separate tribe (Panini) for chimpanzees. In this scheme, “hominin” applies to *Homo*, *Australopithecus*, *Ardipithecus*, and other species that appeared after the split from the chimpanzee line—fossils on the human side are “hominins,” while those on the chimpanzee side are “non-hominin hominids.”

**Cladogram**

The cladogram shows the superfamily Hominoidea and its descendant clades, focusing on Hominini. The family Hominidae includes the tribes Ponginae (orangutans), Gorillini (gorillas), and Hominini, with the last two making up the subfamily Homininae. Hominini splits into Panina (chimpanzees) and Australopithecina (australopithecines). Humans (Hominina) are generally thought to have emerged within Australopithecina—which roughly matches the alternative definition of Hominini that excludes *Pan*.

Genetic and fossil evidence suggests hominoids split from Old World monkeys about 25 million years ago, near the Oligocene-Miocene boundary. The most recent common ancestors of Homininae and Ponginae lived around 15 million years ago. The best-known fossil genus of Ponginae is *Sivapithecus*, with several species dating from 12.5 to 8.5 million years ago; it differs from orangutans in teeth and postcranial features. The cladogram gives approximate times (in millions of years ago) when clades radiated.

**Evolutionary history**

Both *Sahelanthropus* and *Orrorin* lived during the estimated window of the chimpanzee–human speciation events, between 8 and 4 million years ago. Very few fossils can be directly linked to the *Pan* lineage. The first fossil chimpanzee, found in Kenya, was reported in 2005 but is quite recent—between 545,000 and 284,000 years old. The divergence of a proto-human lineage from *Pan* appears to have been a messy process of speciation and hybridization, not a clean split, stretching from as far back as 13 million years ago (close to the origin of Hominini itself) to about 4 million years ago. Different chromosomes seem to have split at different times, with broad hybridization between the two emerging lineages possibly occurring as late as 6.3 to 5.4 million years ago, according to Patterson et al. (2006). That group noted that one hypothetical late hybridization event was based especially on the similarity of X chromosomes in proto-humans and stem chimpanzees, suggesting the final divergence might have been as recent as 4 million years ago. Wakeley (2008) rejected these ideas, offering alternative explanations such as selection pressure on the X chromosome in ancestral populations before the chimpanzee split.