BBC - Earth - We have still not found the missing link between us and apes
The same is true for the relationships among organisms. All of the great apes and humans differ from rhesus monkeys, for example, by about 7% in their DNA. May 18, There was once an animal that was an ancestor to both humans and apes. Lemurs, tarsiers and monkeys are primates, but they have been. This curious situation leads to some questions. Why is it so difficult for evolutionists to determine the human-ape connection from fossils, if we have a common.
But the molecular scientists stuck at their work and, a few decades later, they won over the sceptics — due in no small part to new fossil finds. All manner of fossil primates, including apes, had come to light by the s. One of them, an ape called Ramapithecus or sometimes Sivapithecus, had begun to look a lot like a direct human ancestor.
View image of A jawbone of Ramapithecus Credit: The molecular people said 'See? We were right all along! And if the million-year-old Ramapithecus really was a human ancestor, gorillas and humans cannot possibly have shared a common ancestor just 11 million years ago, as Pauling and Zuckerkandl were suggesting.
But these conclusions about Ramapithecus came almost exclusively from a study of the ape's teeth, which were more or less the only parts of the ancient ape that had been unearthed by the s. In the early s, more Ramapithecus fossils were unearthed, including fragments of the face.
They showed that the ape looked like an orangutan, not a human. Palaeontologists were astonished, but molecular scientists were not. By now they had established that humans, chimps and gorillas were all closely related and shared a common ancestor within the last 11 million years or so, and that orangutans were slightly more distant relatives with a deeper prehistory.
According to their thinking, a million-year-old ape would be unlikely to look distinctly human, because it predated the appearance of the human lineage. But it might well look orangutan-like. In the s and 90s, the molecular community built on such successes. View image of A western lowland gorilla Gorilla gorilla gorilla Credit: Huxley's work in the s had encouraged many scientists to see the LCA as chimp-like, and the molecular work of the s and 90s seemed to vindicate the idea.
Is there a difference between monkeys and apes?
This was not the only conclusion from the molecular work. The DNA studies also put an approximate date on the human-chimpanzee split: It was a figure that considerably narrowed down the search for the LCA. The fossil record shows that apes were widespread across Africa, Europe and Asia about 20 million years ago — at this time the world really was the Planet of the Apes. But by seven million years ago the European and Asian apes had vanished.
If chimpanzees and humans split at this time, the LCA must have lived in Africa — in the same sort of environments occupied by modern chimps. By the early s, 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 s.
View image of Bornean orangutans Pongo pygmaeus Credit: A more thorough understanding of chimp and gorilla anatomy helped. There had been murmurings for some time that gorillas and chimpanzees and bonobos might not knuckle-walk in quite the same way.
Humans aren't monkeys. We aren't apes, either. · john hawks weblog
From subtle differences in the way gorilla and chimpanzee wrist bones change as the apes grow from juveniles to adults, Dainton and Macho concluded that the two may have evolved knuckle-walking independently. Over the following decade, other researchers reported similar findings.
Kivell says the paper received quite a lot of attention. She thinks this might be because it was published just a few months before one of the most complete and potentially important fossils for understanding human evolution was officially unveiled — one that some people think blows a huge hole in the idea that the LCA was chimp-like.
View image of Artist's impression of Ardipithecus ramidus Credit: Put simply, Ardi looked "primitive" White and Lovejoy's careful analysis strongly suggested that Ardi habitually walked on two legs when she was on the ground. It was one of many features that suggested to them that Ardi should be considered an early human, or hominin — one that lived just a few million years after the LCA, and so provides us with our best idea yet of exactly how it looked.
This conclusion was significant, because in many respects Ardi's anatomy is not at all chimp-like. It is very unlikely she was either a knuckle-walker or a brachiating ape.
Ardi lived in a forest setting and must have spent time in trees as well as on the ground. But her anatomy suggests she was adapted to move around in those trees almost like a large monkey might, moving cautiously on feet that — unlike gorilla and chimp feet — seem to have been unsuitable for wrapping around branches for grip.
Put simply, Ardi looked "primitive" — and that suggested that the LCA looked primitive too. Of course, the Ardi analysis was not uncontroversial. One of the implications of their interpretations was that all sorts of anatomical features shared by gibbons, orangutans, chimps and gorillas must have evolved independently in each of these apes. People have begun to question what was an emerging consensus "I think they took it a little too far," says Kivell.
I still think comparative studies with chimps and other African apes can provide a lot of insight into our own evolution. But his own research has also helped to emphasise that chimps might not simply be living time machines from the time that the LCA was alive.
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. They suggested that sexual intercourse lasted longer in the LCA than in chimpanzees, and that the LCA males devoted more time to looking after offspring than chimp males do.
Apes were still flourishing in Europe as well as Africa 13 million years ago Decades after Straus and a few other anatomists had argued that the chimpanzee was a poor model for the LCA, mainstream opinion has moved their way.
But even that is not the end of the story.Why Aren't Apes Still Evolving Into Humans? - Dolan Life Mysteries
There are still "chimp-like LCA" advocates out there, and they are fighting back. For instance, in Young and his colleagues argued from the study of ape shoulder blades that the LCA might have had some features in common with chimps and gorillas after allhinting that it might actually have been a brachiating ape. Such a conclusion would not have been controversial if it had been published a decade or so ago, Young says — but mainstream thought has shifted so far from the chimp-like LCA concept that the paper did, in fact, face some criticism.
Of course, only if and when fossils of the LCA itself come to light will the debate finally draw to a close. But the search for those crucial fossils is no longer quite as straightforward as it once seemed.
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.
View image of Artist's impression of a Dryopithecus Credit: David Begunan anthropologist at the University of Toronto in Canada, concluded that Dryopithecus might be an early relative of the gorillaand suggested that the LCA of humans and chimps might consequently have lived about 10 million years ago.
There are also a few researchers who take a completely different view. There is not yet universal agreement For instance, Schwartz is adamant that it is orangutans, not chimpanzees, that are our sister species. It is an idea he first developed in the s — before, he says, anthropologists "caved in" and conceded that molecules and not anatomy were the ultimate arbiters of the shape of the ape family tree.
Schwartz thinks DNA is not the infallible witness on evolution many assume it to beand that there are many anatomical and behavioural similarities between humans and orangutans that should not simply be ignored. For instance, both have thick layers of enamel on their teeth, and female orangutans like women do not "advertise" to males when they are most fertile — something biologists call oestrus.
To be clear, few researchers agree with Schwartz. But even putting his ideas to one side, it is clear that there is not yet universal agreement on the LCA. It is true that, today, some researchers have a well-thought-through idea of what the LCA looked like and how it behaved.
Evolution is the cornerstone of modern biology. There is no scientific controversy about whether evolution occurred or whether it explains the history of life on Earth. As in all fields of science, knowledge about evolution continues to increase through research and serious debate.
For example, scientists continue to investigate the details of how evolution occurred and to refine exactly what happened at different times. How do scientists know the age of fossils? Scientists have developed more than a dozen methods for determining the age of fossils, human artifacts, and the sediments in which such evidence is found.
These methods can date objects millions of years old. Read more about dating methods here. How do scientists know what past climates were like?
Among the major sources of evidence are sediment cores from the ocean bottom. They preserve the fossils of tiny organisms called foraminifera. By measuring oxygen in the skeletons of these organisms, scientists can calculate fluctuations in temperature and moisture over millions of years.
- Humans aren't monkeys. We aren't apes, either.
- We have still not found the missing link between us and apes
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What has been discovered about evolution since Darwin? Since Darwin died infindings from many fields have confirmed and greatly expanded on his ideas. Can the concept of evolution co-exist with religious faith? Some members of both religious and scientific communities consider evolution to be opposed to religion. But others see no conflict between religion as a matter of faith and evolution as a matter of science.
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