Gorillas are iconic primates, and tracing their evolutionary history involves piecing together evidence from modern genetics and a sparse fossil record. The question of what gorillas evolved from points not to a single species, but rather a branching point on the tree of life that occurred millions of years ago. Their story is one of divergence from a shared African ancestor, a complex process involving environmental shifts and the independent evolution of closely related lineages. Understanding their origins requires looking at their place among all the great apes and the timing of their split from their closest relatives.
Gorillas in the Great Ape Family
Gorillas hold a specific place within the biological family Hominidae, which includes all great apes (orangutans, chimpanzees, bonobos, and humans). Within this classification, gorillas belong to their own tribe, Gorillini, distinguishing them from the tribe Hominini, which encompasses chimpanzees, bonobos, and humans.
Genetic information confirms the close relationship between these African apes and humans. Gorillas are the next closest living relatives to humans after chimpanzees and bonobos. Their DNA is highly similar to that of humans, with genetic differences averaging around 1.6% across certain analyzed genes. This close relationship sets the context for determining the evolutionary timeline.
Tracing the Divergence: The Common Ancestor Split
The chronological split separating the gorilla lineage from the line leading to chimpanzees and humans is estimated to have occurred roughly 8 to 10 million years ago during the Late Miocene epoch. This timing is determined through molecular clock analysis, a technique that uses the rate of genetic mutations to estimate when two species last shared a common ancestor. This analysis suggests the gorilla divergence occurred before the split between chimpanzees and humans.
The species existing just before this separation is called the Last Common Ancestor (LCA) shared by all African apes and humans. While no definitive fossil evidence of this hypothetical creature exists, it was likely a large-bodied, tree-climbing ape. Following this initial separation, environmental pressures, such as a changing climate and the fragmentation of African tropical forests, drove the gorilla lineage down a distinct evolutionary path.
The precise timing of the split continues to be refined as new genetic and fossil evidence emerges. Molecular studies often estimate the separation time for the gorilla lineage from the human-chimpanzee line to be closer to 10 million years ago. The continuous refinement of mutation rates and the integration of new fossil finds help to better align molecular dating with the physical evidence of the past.
The Fossil Record of Early Gorilla Ancestors
The physical fossil evidence of the early gorilla lineage, particularly following the divergence, remains exceptionally scarce. However, a few significant finds offer potential insights into the gorilla’s direct ancestry.
One such fossil is Nakalipithecus nakayamai, discovered in Kenya and dated to approximately 9.9 million years ago. Based on the fossilized jawbone and teeth, Nakalipithecus is considered very close to the last common ancestor of all African great apes and humans. Its dental features, such as thick enamel, suggest a diet that included hard objects, possibly nuts and seeds. The age of this fossil places it close to the estimated time of the gorilla-human/chimpanzee split, making it a strong candidate for a stem gorilla line relative.
Another potential candidate is Chororapithecus abyssinicus, an ape known from isolated teeth discovered in Ethiopia and dated to about 8 million years ago. The teeth of Chororapithecus are similar in size and proportions to those of modern gorillas, leading some researchers to propose it represents an early member of the Gorillini tribe. The scarcity of remains makes this classification challenging, as anatomical differences exist between its teeth and those of modern gorillas. Despite the limited physical evidence, these fossils support the idea that the ancestors of the African great apes evolved in Africa during the Late Miocene.