Chimpanzee–human last common ancestor

The chimpanzee–human last common ancestor (CHLCA) is the last shared ancestor between humans and the species we call chimpanzees and bonobos. Scientists study this ancestor to learn more about how humans and these close relatives are connected.

Estimates suggest that humans and chimpanzees shared this common ancestor between five and thirteen million years ago. This time frame helps scientists understand how our species has changed over millions of years.

In studies of human genetics, the CHLCA serves as an important reference point. By comparing human DNA with chimpanzee DNA, scientists can calculate how quickly genetic changes occur in human populations.

Although researchers have searched for fossils of this ancestor, none have been found yet. Some ancient fossils, like Sahelanthropus tchadensis, Orrorin tugenensis, and Ardipithecus ramidus, might be related to the CHLCA, but scientists are still unsure because the fossils are incomplete.

Taxonomy

Main article: Hominini

The group called Hominini was created to separate humans (genus Homo) from chimpanzees (Pan) and gorillas (genus Gorilla). Later, scientists found that chimpanzees and humans are more closely related to each other than chimpanzees are to gorillas. Because of this, chimpanzees were grouped with humans in the Hominini tribe, and gorillas were placed in a separate group called Gorillini.

Some scientists suggested dividing Hominini into two smaller groups. They placed humans and other walking apes in a group called Hominina, and chimpanzees in another group called Panina.

All human-related groups that came after the split from chimpanzees belong to the subtribe Hominina, including humans (Homo) and Australopithecus. These groups are known as "hominins".

Fossil evidence

Scientists have not found any fossils that can clearly show us the last common ancestor of humans and chimpanzees. Some ancient fossils, like Sahelanthropus tchadensis and Orrorin, lived around the time humans and chimpanzees split apart from each other, about 7 million years ago. These fossils have some features that are similar to both humans and chimpanzees, but it is hard to tell if they are direct ancestors or just close relatives.

Another fossil, Ardipithecus, appeared after the split, around 5.5 million years ago. It shares some traits with chimpanzees but is not complete enough to know its exact place in our family tree. Because fossils from this time are rare, scientists are working on new ways to study them using computers to learn more about our shared ancestors.

Age estimates

Scientists have tried to figure out when humans and chimpanzees last shared a common ancestor. In 1998, they thought it might have been between 10 to 13 million years ago. By 2009, some researchers suggested it was between 7 to 10 million years ago.

More recent studies, like one from 2022, suggest it might have been between 6.6 and 4.7 million years ago. A 2025 study, using full genome sequences, estimated the split happened between 6.3 and 5.5 million years ago.

Gene flow

The exact time when chimpanzees and humans last shared a common ancestor is tricky to figure out. Instead of splitting apart all at once, different parts of their DNA separated over millions of years. This slow process included mixing of genes between the two groups as recently as between 6.3 million and 5.4 million years ago.

Scientists believe the split between chimpanzees and humans happened over the last 9 million years. After the first split, there were more periods where the groups mixed their genes and then separated again. The final split happened sometime between 13 million and 4 million years ago, though scientists debate the exact timing. This complex mixing makes it hard to pin down a single date for when humans and chimpanzees last shared a common ancestor.