Evolution and humans: We don't know our parents (Evolution)

by David Turell , Thursday, July 20, 2017, 01:38 (2682 days ago) @ David Turell

There is a last common ancestor for the human and the ape lines, not yet identified. No question, we split off from someone not yet found:

http://www.bbc.com/earth/story/20170517-we-have-still-not-found-the-missing-link-betwee...

"The idea led to two inescapable conclusions. First, our species is not an only child. Somewhere out there in the natural world, there is at least one species of animal that is more closely related to humans than any other – what biologists would come to call humanity's "sister species".

"Secondly, and as importantly, our species has a long-lost parent. It stands to reason that if humanity has one or more sisters, then these siblings must have shared the same parent species at some point in prehistory. Evolutionary biologists call this species the "last common ancestor" (LCA). Most people know it by a non-scientific name: the "missing link".

"Scientists have been on the trail of the LCA for decades, and they still have not found it. But many are convinced that they have established enough information to make the hunt a lot easier. They think they know roughly when and where the LCA lived. They even have a reasonable idea of what it looked like and how it behaved.

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""Lesser" apes like the gibbons offered a window into the anatomy of our earliest ape ancestors. Meanwhile the "great" apes – gorillas, chimpanzees and orangutans – showed the anatomical features our ancestors possessed at the moment they split away from the other apes and began to develop a uniquely human appearance. Gorillas and chimps were not simply our sister species: they were also a lot like the LCA.

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"It might seem absurd to argue that our highly developed brain is anything other than an example of primate evolution pushed to the extreme. But human arms, hands, legs and feet are not as highly specialised as we might assume.

"'In these characters man finds his counterparts not in anthropoid apes [gorillas, chimpanzees and orangutans] but in animals that are clearly regarded… as more primitive," wrote Straus.

"What Straus and a few others were really getting at is that humans show none of the specialised features that allow other apes to swing through the trees. It made sense to at least consider the possibility that humans split apart from other primates before the apes evolved brachiation, or knuckle-walking for that matter.

"Straus could not say exactly which species should be recognised as our sister. But the LCA could well have been a relatively small-bodied primate that ran along branches rather than swinging beneath them.

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"Working with his colleague, Emile Zuckerkandl, Pauling developed a truly revolutionary idea: the molecular clock......Their paper articulated the assumption that molecules are constantly changing, and the more ancient the divergence between species, the more time those species have had to accumulate their own molecular differences."

Pauling and Zuckerkandl used this concept – that some molecules accumulate tiny changes at a steady rate – to analyse proteins in human and gorilla blood. From the number of differences between the two sets of molecules, and an estimate of the rate that those differences accumulate, the researchers calculated that humans and gorillas had last shared a common ancestor roughly 11 million years ago.

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"By the early 2000s, some physical anthropologists were even describing African apes like the chimpanzee as time machines into the earliest stages of human evolution.

"The story should end there, but it does not. Surprisingly, the last 15 years has actually seen popular opinion begin to swing away from the idea of a chimp-like LCA, and towards a model closer to that argued by people like Straus in the 1940s.

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"By 2009, Tracy Kivell – now at the University of Kent, UK – and Daniel Schmitt at Duke University in Durham, North Carolina, were arguing that humans did not evolve from a knuckle-walking LCA.

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"Judging by fossil evidence from earlier apes, human hands are surprisingly primitive in appearance – notwithstanding the fact that we evolved an opposable thumb after the split from the LCA.

"Even the biologists studying modern primates are finding evidence that the LCA may not have been chimp-like.

***

"In the last five years, some geneticists have begun to question whether the molecular clocks they use to estimate when the LCA lived are being read correctly. It is possible, they say, that the LCA might actually have lived 13 – not seven – million years ago.

"Apes were still flourishing in Europe as well as Africa 13 million years ago, which means that in principle the LCA might have lived there."

Comment: The book Not a Chimp , 2009, points out that our DNA in action when analyzed is only 78% similar to chimps.