Hominins: Appearance, Expansion, and Extinctions

Appearance of Hominins Through Time

Separation from African Great Apes

Hominins include all species related to modern humans (Homo sapiens) after their divergence from the chimpanzee lineage. Paleogenetic analyses and fossils suggest that this split occurred between 7 and 6 million years ago, during a period of major climatic transformations in Africa.

The First Hominins of the Late Miocene

The first recognized representative is Sahelanthropus tchadensis (≈ 7 Ma), discovered in Chad. Its skull, featuring an advanced foramen magnum, indicates a partially bipedal posture. It is followed by Orrorin tugenensis (≈ 6 Ma, Kenya) and Ardipithecus kadabba (5.8–5.2 Ma), which already show locomotor adaptations indicating a transition from an arboreal lifestyle to bipedalism.

Australopithecines: Affirmed Bipedalism

Between 4.5 and 2 million years ago, australopithecines emerged as the dominant hominins. Australopithecus afarensis (3.9–3.0 Ma), known from the famous "Lucy" fossil, embodies more pronounced bipedalism, although its cranial capacity (~400 cm³) remains close to that of great apes. These species were contemporary with ecological diversification, occupying varied niches from wooded environments to more open savannas.

The Genus Homo: Technical and Cognitive Emergence

Around 2.5 million years ago, the appearance of the genus Homo marked a major evolutionary turning point. Homo habilis and Homo rudolfensis are associated with the first lithic tools (Oldowan industry), indicating new cognitive abilities. Soon after, Homo erectus (1.9 Ma) became the first great colonizer of the world, leaving Africa to populate Asia and Europe, mastering fire, and developing organized societies.

Diversification of the Genus Homo in the Pleistocene

Over the last million years, the human lineage became more complex with Homo heidelbergensis, Homo neanderthalensis, the mysterious Denisovans, and island species such as Homo floresiensis and Homo luzonensis. Finally, Homo sapiens, which appeared in Africa about 300,000 years ago, is distinguished by the emergence of symbolic language, art, and cumulative culture, leading to today's planetary diversity and dominance.

A Bushy, Non-Linear Evolution

Thus, the evolution of hominins, spanning over 7 million years, illustrates a complex process of diversification and extinction, where several species coexisted before our species became the sole survivor of the genus Homo. This bushy evolution demonstrates that humanity is not the result of linear progression, but of an intertwining of parallel lineages shaped by natural selection, climate, and culture.

Table of Main Hominin Species

Sources: Smithsonian Human Origins Program, MNHN Paris, Leakey Foundation, Berger et al. (2015), Stringer (2022).