Original great ape? Probably not
|May 2, 2013||Posted by News under News|
An 11.9 million-year-old ape fossil discovered in Catalonia, Spain, in 2002, and subsequently given the name Pierolapithecus catalaunicus, lived around the time when the great apes first appeared, according to Dr. Ashley Hammond, a University of Missouri anatomical expert who examined the creature’s pelvis and co-authored a recent study describing its morphology. Science Daily has a report on the study by Hammond et al., which is entitled, Middle Miocene Pierolapithecus provides a first glimpse into early hominid pelvic morphology, and which is due for publication in the Journal of Human Evolution later this year. Non-scientist readers who would like to know more about the fossil ape might like to read Victoria Woollaston’s report in The Daily Mail, here: it’s refreshingly jargon-free and has lots of great illustrations.
Hammond has carefully avoided making inflated claims for the fossil she examined: “Contrary to popular belief, we’re not looking for a missing link,” she says. Nevertheless, she feels confident that Pierolapithecus lived near the beginning of the time when the great apes first appeared, but before they had begun to diversify into humans, chimps, gorillas and orangutans. Additionally, she believes that the fossil ape dates from some time after the split between the great apes and the lesser apes (gibbons and siamangs), which are much smaller in size, and have relatively longer arms and smaller brains than the great apes. In plain English: if Pierolapithecus isn’t the original great ape, it’s a very near relative: close enough to a common ancestor of humans, chimps, gorillas and orangutans.
Hammond’s report goes on to add that Pierolapithecus had a wider pelvis than earlier fossil apes, which may be related to the ape’s need for greater lateral balance and stability while using its forelimbs. It seems to have engaged in a variety of upright activities, including vertical climbing. However, it lacked the long, curved finger bones that an ape would need for suspending itself from a tree branch. In an interview, Hammond stated:
“Today, great apes such as chimpanzees, orangutans, bonobos and gorillas use forelimb-dominated behaviors to swing below branches. But Pierolapithecus catalaunicus didn’t have the long, curved finger bones needed for suspension, so those behaviors evolved more recently.”
So, has the original great ape been found? Probably not. In fact, there are several good reasons to be skeptical of the proposal that Pierolapithecus may have been the ancestor of all great apes.
1. The date: is the fossil too young?
As the Science Daily report correctly noted, Pierolapithecus catalaunicus is only 11.9 million years old. But the fossils of the oldest known orangutan ancestor, Sivapithecus, date from 9 to 13.9 million years ago, which suggests that the new fossil may be ancestral to African apes but not the orangutan.
As if that were not bad enough, the molecular clock has recently been recalibrated by some scientists, who now date the human-chimp split to around 8 to 10 million years ago, instead of 4 to 7 million years ago, as was believed until recently. In a report published in Proceedings of the National Academy of Sciences last year, Langergraber et al. estimated the human-chimp split to have occurred somewhere between 6.8 and 11.6 million years ago, and the human-gorilla split between 10.9 and 17.2 million years ago (Generation times in wild chimpanzees and gorillas suggest earlier divergence times in great ape and human evolution, PNAS, 39, vol. 109, pp. 15716-15721, 25 September 2012). If that’s the case, then the supposed common ancestor of orangutans, humans, chimps and gorillas must have been considerably older. Around the same time last year, Aylwyn Scally and Richard Durbin published a review of molecular clock research conducted to date, (“Revising the human mutation rate: implications for the understanding human evolution” in Nature Reviews Genetics 13:745-753, October 2012, doi:10.1038/nrg3295) and suggested that the molecular clock used to date events in hominid prehistory may run more slowly than previously thought.
One startling implication of the new research, pointed out by science writer Ann Gibbons in a report in Science magazine (Vol. 338, 12 October 2012), entitled, Turning Back the Clock: Slowing the Pace of Prehistory, is that the date of the split between orangutans and other great apes would have to be revised upwards from 13-14 million years ago to anywhere from 34 to 46 million years ago – an impossible result that has researchers scratching their heads. “A human-orangutan split at 40 million years is absolutely crazy,” says paleoanthropologist David Begun of the University of Toronto, St. George, in Canada.
Scally and Durbin have attempted to explain away this problem by suggesting that the mutation rate was faster early on in primate evolution, and that it later slowed in the African apes. But the slowdown proposed would have to have been extraordinarily dramatic, argues Harvard University population geneticist David Reich, in a supplement to a paper he and his research team recently published (Nature Genetics, 44, 1161-1165 (2012), doi:10.1038/ng.2398). Reich estimates the split between orangutans and other great apes to have occurred 2.65 times earlier than the human-chimp split. So if 11.9 million-year-old Pierolapithecus catalaunicus is the original great ape, then humans and chimps split only 4.5 million years ago – which would mean that fossils of creatures such as Sahelanthropus, Orrorin and possibly also Ardipithecus, would no longer be on the line leading to human beings – a result that is not likely to make paleoanthropologists happy.
2. The location: shouldn’t it be in Africa or Asia, rather than Europe?
Since all the existing great ape species live in either Southeast Asia or Africa, the idea that Pierolapithecus, which lived in Spain, was an ancestor of all modern great apes doesn’t make a lot of sense. Also, most of the evolution of great apes and humans is supposed to have taken place in Africa.
It has been suggested that since the Mediterranean Sea expanded and contracted frequently in the past, Pierolapithecus could well have lived on two continents: Europe and Africa. But Professor David Pilbeam, who is currently Henry Ford II Professor of the Social Sciences at Harvard University and curator of paleoanthropology at the Peabody Museum of Archaeology and Ethnology in Cambridge, Massachusetts, USA, has pooh-poohed the idea that Pierolapithecus may be ancestral to modern great apes: “To me it’s a very long stretch to link this to any of the living apes,” he told BBC News in a 2004 interview, shortly after the original paper describing the ape was published in Science magazine (19 November 2004: Vol. 306 no. 5700, pp. 1339-1344). He added: “I think it’s unlikely that you would find relatives of the apes that live today in equatorial Africa and Asia up in Europe.
3. Anatomy: the fossil may not be ancestral to orangutans
David Begun, professor of paleoanthropology at the University of Toronto, Canada, told The New York Times in a 2004 interview that certain aspects of the fossil specimen’s face, palate and teeth made him inclined to believe that the species might be located farther down the evolutionary line of great apes than the common ancestor. In a BBC interview that same year, he explained his reasons for doubting that the creature was ancestral to orangutans: “I haven’t seen the original fossils. But there are four or five important features of the face, in particular, that seem to be closer to African apes. To me the possibility exists that it is already on the evolutionary line to African apes and humans.”
4. Rival contenders: a hodge-podge of hominids
It turns out that Pierolapithecus had lots of company. Not only did he have a contemporary, who lived in the same area – another mid-Miocene ape from Spain, named Anoiapithecus brevirostris, who also dates back to 11.9 million years ago – but there were ten other genera of apes from East Africa that may have been in the lineage leading up to the first appearance of the great apes, estimated by many scientists to have occurred around 13 million years ago: Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, an ape considered by some experts to have been the true ancestor of all great apes.
Other creatures from around that time include Otavipithecus, which is known from cave deposits in Namibia, and the monkey-like Dryopithecus, known from several sites in Eurasia and Africa.
To be fair, I would like to point out that Dr. Victoria Hammond, who examined the pelvis of Pierolapithecus recently, has downplayed the claim that this creature might have been the ancestor of all great apes. But the claim has a long history: it was made as far back as 2004 and is still made today. It’s about time that somebody punctured Pierolapithecus‘s balloon with a healthy dose of skepticism. Interesting ape fossil? Sure. But missing link it almost certainly ain’t.
The only thing we know is that we don’t know
Some of us are old enough to remember the times when the term “hominid” referred to a family believed to contain humans and their prehistoric ancestors but not the great apes (gorillas, chimps and orangutans), who were classed in a separate family: Pongidae. Back in those days, Ramapithecus was widely touted as the ancestor of the hominids. Now Ramapithecus has been wiped off the map, as a taxon: it’s been reclassified as Sivapithecus, and far from being a human ancestor, it’s now regarded as being on the line leading to orangutans. Humans are now placed in the same family as chimps, gorillas and orangutans. At the present time, just about the only thing one can confidently say about any hominid fossil is that any claims that are currently made about its place in our family tree are almost certainly wrong. There’s still a lot we don’t know yet.
What’s really puzzling, though, is that more scientists aren’t sitting up and taking notice of a very impressively researched paper by Dr. Branko Kozulic, entitled, Proteins and Genes, Singletons and Species, showing that that the sequenced genome of each species contains hundreds, or even thousands, of unique genes – the genes that are not shared with any other species. Kozulic argues that these unique genes and proteins, singletons, define the character of each and every species, and calculates that the odds of these proteins appearing as a result of undirected processes are astronomically low. Now that’s a finding that should give every Darwinist a massive headache. Stay tuned!