The Last Common Ancestor of Chimps and Humans?

Co-Authored with the New Bing

A question that is often asked of anthropologists is how related we are to chimpanzees, bonobos, and the other great apes. The answer is that we are very related, in fact, we share 98% of our DNA with chimps and bonobos. But why is this? The short answer is that we share a recent last common ancestor, or “LCA”, this means that our two species diverged from the same ancestor somewhat recently in geologic time, about 6-7 million years ago.

The last common ancestor of chimps and Homo sapiens is a fascinating topic in Paleoanthropology, as it sheds light on our closest living relatives’ evolutionary history and divergence. However, identifying and characterizing this ancestor is difficult, as many uncertainties and controversies surrounding its morphology, behavior, ecology, and genetics exist.

One of the first challenges is to estimate when the last common ancestor (LCA) lived. This can be done by comparing the DNA sequences of living, also known as extant, humans and chimps and calculating how long it would take for them to accumulate the observed differences due to mutations. This method, known as the Molecular Clock, gives the LCA an approximate date of 6 to 7 million years ago (mya). However, this date may not be accurate, as different genes may evolve at different rates, and there may have been episodes of gene flow or hybridization between the two lineages after their initial split. Therefore, fossil evidence is also crucial to corroborate or refine the molecular estimates.

Unfortunately, the fossil record of the LCA and its early descendants is very scarce and fragmentary. Most of the fossils that have been attributed to this period are from Africa, where the LCA is presumed to have originated. However, some recent discoveries suggest that Europe may also have played a role in the evolution of hominins (the human clade). For example, Graecopithecus, a fossil ape from Greece and Bulgaria, has been dated to about 7.2 mya and has some dental features that resemble those of hominins. Some researchers have proposed that Graecopithecus may represent the LCA or a close relative, implying that the split between humans and chimps occurred in Europe rather than Africa. However, this hypothesis is controversial and not widely accepted by most Paleoanthropologists.

Another challenge is to reconstruct what the LCA looked like and how it behaved. Many researchers have assumed that the LCA was similar to a modern chimpanzee, based on the idea that chimps have retained more primitive traits than humans. However, this view has been challenged by recent studies that show that both humans and chimps have evolved many unique features since their divergence from the LCA. For example, chimps have more genes modified by natural selection than humans, suggesting that they have adapted to their specific environments and lifestyles. Moreover, chimps exhibit a great diversity of behaviors across different populations and regions, indicating that they are not static or uniform in their culture and ecology.

Therefore, it is likely that the LCA was different from both humans and chimps in many aspects. Some possible characteristics of the LCA that various researchers have suggested are:

– It was bipedal, at least partially, as this trait is shared by all hominins and may have originated before the split from chimps.

– It had a relatively small brain size, similar to or slightly larger than that of a modern chimp.

– It had a mixed diet of fruits, leaves, nuts, seeds and animal foods, as indicated by its dental morphology and isotopic signatures.

– It lived in a mosaic habitat of woodlands and grasslands, as inferred from its locomotion and diet adaptations.

– It had a complex social structure and communication system, as these are common features of all apes and may have been present in their common ancestor.

Of course, these are only tentative hypotheses based on limited evidence and may change as new fossils and genetic data are discovered. The LCA remains a mysterious and elusive entity in our evolutionary history, but also a fascinating one that can help us understand ourselves better.

Sources:

– The last common ancestor of humans and chimps probably wasn’t much like either – Science News

– Gorilla–human last common ancestor – Wikipedia

– Here’s What the Last Common Ancestor of Apes and Humans Looked Like – Live Science