Did the LCA Have Teeth More Like a Gorilla?

Artificial intelligence is playing a role in understanding human evolution.  From the Australian site News.com comes a story about new work in trying to understand what the last common ancestor to apes and humans might have looked like:

IT’S an image imprinted on our brains: the steady march of evolution from chimp to human. But it’s not quite right.

Monkeys don’t belong on the tree. They have tails.

Chimps, which don’t, are with Bonobos our closest living relatives. And, as such, both should be standing alongside us in the march of life.

Stretching out behind should be a gradually converging branch of earlier variations.

Ultimately, between six and eight million years ago, the branches almost certainly converge on one common ancestor.

We know almost nothing about what that was.

We have reasonably secure evidence of bipedality at around 6 million years in the form of Orrorin tugenensis from Kenya, as well as a crushed skull from Chad called Sahelanthropus that may or may not be 7 million years old, and recently, fossil footprints, purporting to show bipedal walking, from Crete have been uncovered that have been dated to around 5.7 million years ago.  Beyond that, nothing.  That is where the new AI study comes in.

The researchers used machine learning to teach an artificial intelligence to identify and classify fossilised hominid teeth dating from 25 million years ago. It then sifted through these to find patterns of development.

The study published in the science journal PaleoBios found one tantalising tip.

Our common ancestor almost certainly had gorilla-like teeth.

Now, it’s not a lot. And it certainly doesn’t say our ancestor was a gorilla.

But what it does do is add some shape and substance to this nebulous period of our human origins.

The information that is contained in the article is not nearly as cut and dried as is indicated by the news story. From the conclusion:

Given that the divergence of humans and chimpanzees occurred in the late Miocene, and that Miocene apes are much more similar to Gorilla in dental proportions, we assert that gorillas are the more appropriate extant model for the African ape LCA in terms of the relative sizes of the postcanine teeth. This similarity in dental proportions likely has implications for the interpretation of dietary adaptation and possibly phylogenetic relationships in Miocene apes, including the chimpanzee-human last common ancestor.

What this likely means is that, during the Miocene, which was the golden age of the apes, even after the divergence of Gorillas from the main line, there were extant forms that continued to have varying degrees of traits that could be associated with gorillas, presenting a classic case of collateral ancestry.  It is possible that one of the lines eventually led to chimpanzees, while another led to us.  We won't know more until we actually have some fossil remains from that missing time period. 
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Human/Gorilla Split at Eight MYA?

Scientific American is running an article, which details work by Gen Suwa and colleagues, in the Afar Triangle, where nine gorilla-sized teeth were found in 2007 that have now been securely dated to around eight million years ago.  The researchers named the species Chororopithecus abyssinicus.  Charles Choi writes: 

The age and location of these fossils strengthen the view that the human and the modern ape lines originated in Africa and not Asia, the researchers said.

"Until now, no mammalian fossils south of the Sahara have been securely dated to 8 million to 9 million years ago," Suwa said. "Any and all fossils from this crucial time period of Africa would help unravel the story of human origins and emergence. These are the first such fossils."

In addition, until recently, "most scientists, especially geneticists, thought that the human-chimp split was as recent as 5 million years ago, and that the human-gorilla split was only about 7 million to 8 million years ago," Suwa said. "This contradicted the fossil record. For example, fossils thought to be on the human side of the split such as Ardipithecus kadabba from Ethiopia and Sahelanthropus from Chad were 6 million years old — or, in the case of the Chad fossil, perhaps 7 million years old."

The new findings suggest that Chororapithecus is 8 million years old, so "the actual gorilla-human split must then have been up to several million years before that," Suwa said.

More pieces to the puzzle. The other mystery, of course, is when the last common ancestor of humans and chimpanzees lived.

Gorilla DNA Sequenced

According to a story out of the LA Times, the gorilla genome has been completely sequenced. Eryn Brown writes:

By comparing the new gorilla DNA sequence with reference genomes of humans, chimpanzees, orangutans and macaques, scientists have already made a few surprising insights into the crucial periods when we diverged into separate species.

For instance, the new genetic data bolster fossil evidence that gorillas split off as a separate species about 10 million years ago and that humans and chimps parted ways about 6 million years ago. Previous genetic evidence had seemed to point to a more recent split, prompting a contentious debate between genetics experts and fossil scholars, said Durbin, who leads the genome informatics group at the Wellcome Trust Sanger Institute in Hinxton, England.

This is good because it means that the last common ancestor can be as far back as six to seven million. Does this make Sahelanthropus or Orrorin hominins? Not necessarily but now it is a more easily acceptable position..

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