Hominins
The term hominin is used extensively in the scientific literature, although it has not yet been adopted widely in popular writing. The tribe Hominins defines current humans and our extinct ancestors as a distinct group; it does not include our closest living relatives. As Phillip Tobias (1971) put it, a distant relative of modern humans initiated the necessary evolutionary thrust to establish a new phyletic lineage, different from that of gorillas and chimpanzees. The hominin taxon includes humans and their direct or collateral ancestors that are not also ancestors of other living hominoids.
The most plausible cladogram that represents the phyletic relationships between higher apes and humans considers chimpanzees as the sister group of current humans. There are two possible phylogenetic interpretations of fossils belonging to early genera, such as Orrorin, Ardipithecus, Kenyanthropus, Australopithecus, or Paranthropus. The first option is to place them within the lineage of current humans (the one leading to the genus Homo). The alternative is to consider them as ancestors of chimpanzees or gorillas. The first option implies that the specimens are hominins, pre-humans. The lateral branches of our lineage's evolution, such as the robust australopiths (Paranthropus) are considered hominins.
Chimpanzees share a clade with us to the exclusion of gorillas and orangutans. Why do we not also consider them hominins? They have striking derived traits. We classify certain fossil specimens as hominins even though they exhibit derived traits which arc remarkably different from our own. However, there is a critical difference between the chimpanzees and the fossils that we classify as hominins; namely, that the former are living organisms. It is not obvious how chimpanzees would be classified if they had gone extinct soon after their appearance and their remains had been found. The interpretation of human evolution is strongly influenced by current living hominoid species.
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