Tuesday, February 16, 2016

Gorillas and humans diverged from one another earlier than thought

Studying ancient humans and primates tells us more about our owns selves and what it means to be human, what it means to be of the species modern Homo sapiens. While we can look at our closest living relatives, apes and other primates, to theorize a great deal about how our ancestors acted  5 million years ago (mya), we also rely on fossil evidence and genetic studies. Studying human ancestors presents one very large problem: lack of fossil evidence. The fossilization process requires just the right conditions at time of death and the right conditions afterwards.  Thus, there are many gaps in our knowledge because the data simply isn't available. The fossils haven't been found.

Juvenile mountain gorillas, Photo credit: Philip Milne
Scientists are particularly interested in fossils from 12-7 mya because this is around the time when African apes (gorillas, chimpanzees, and bonobos) and humans split. Yet, few fossils from this time have been discovered.

Katoh and colleagues (2016) studied fossilized teeth found in Ethiopia's Afar Rift from an ancestral gorilla, called Choroapithecus abyssinicus, and the surrounding layers of earth these fossils were found in. Their results that suggest C. abyssinicus is older than previously believed. The teeth have been dated to 8 mya, which would mean that these ancestral gorillas and ancestral humans had to have diverged earlier in time than previously thought.

Previous estimates of the split between African apes and humans suggested the two lines diverged more recently. Data from genetics suggests that humans and gorillas split somewhere between seven to eight million years ago.  When C. abyssinicus was first discovered, it was found in deposits that are older than 8mya. The geology previously suggested that this species lived 10-10.5 mya (Suwa et al., 2007). Thus, this study provides some needed clarity on the age of these fossils.

With these new results, we can place the age of these fossils at 8 mya, meaning this ancestral ape and humans likely split around 10 mya rather than 8 mya and suggesting the mutation rate between the two was slower than previously thought. We can also confirm that ancestral great apes evolved in Africa, as opposed to Europe or Asia.

It's always impressive how a few extra teeth and a lot of hard work can transform what we know about our own origins.

Works cited:

Katoh, S., Beyene, Y., Itaya, T., Hyodo, H., Hyodo, M., Yagi, K., ... & Nakaya, H. (2016). New geological and palaeontological age constraint for the gorilla–human lineage split. Nature, 530(7589), 215-218.

Suwa, G., Kono, R. T., Katoh, S., Asfaw, B., & Beyene, Y. (2007). A new species of great ape from the late Miocene epoch in Ethiopia. Nature, 448(7156), 921-924.

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