How Many Human Body Parts Remain Undiscovered?
May 6, 2011 --
Neanderthals shared Europe with a mysterious member of our genus that may represent an entirely new species of human, suggests a paper accepted for publication in the Journal of Human Evolution. The study describes the recently unearthed remains of a hominid from what is now Serbia. The remains -- a fossilized jaw and teeth -- date to at least 113,000 years ago.
"The specimen is primitive and does not show any Neanderthal-derived traits," lead author Mirjana Roksandic told Discovery News. "It could be a simple case of one non-representative member of a larger population that is morphologically primitive, or a representative member of a more primitive population that remained in the Balkans while Neanderthals developed in the rest of Europe." Roksandic, an associate professor of anthropology at the University of Winnipeg, and her team have not, however, ruled out that the individual belonged to a new Homo species. Europe appears to have been home to several such species over the past 1.7 million years, including Homo georgicus, Homo antecessor, Homo heidelbergensis and Homo neanderthalensis.
For the study, the researchers performed a CT scan and other analysis of the jaw and teeth that were discovered at Mala Balanica Cave in Serbia. Co-author Dusan Mihailovic told Discovery News that "a rich tool assemblage" was found in an upper part of the geological sequence at the site. Additional excavation work may uncover older tools, he said.
The cave complex is located in a Central Balkans region that has been called a "hotspot of biodiversity." "Hotspot of biodiversity as a characteristic of the Balkans was put forward by biogeographers to indicate that most of the plant and animal species that repopulated the continent after glaciations came from the Balkans," Roksandic explained. "In the north of the continent all species of the eastern, and a fair number of the western, part are from the Balkans source." It remains unclear whether or not a new human species originated in the Balkans. This region was never very isolated, as its southern portion remained open throughout the Pleistocene. The new Homo discovery is therefore all the more puzzling.
The researchers cannot conclude much about its possible appearance and behavior, but they can tell it possessed a large jaw and small teeth relative to other known human fossils. Muscle markings associated with the jaw "are not prominent," according to Roksandic.
The fate of Neanderthals and the Serbian individual's group remains unclear, but prior research has determined that modern humans did interbreed, at least to some extent, with Neanderthals. Other anthropologists have suggested that modern humans also may have interbred with additional Homo species from Europe. "It would probably be best to describe Neanderthals and other Pleistocene humans as morphospecies," Roksandic said. "This acknowledges differences but does not discuss their phylogenetic relationship. They are morphologically different, (so) would it prevent them from recognizing each other as potential mates? Hard to say." She added that according to some researchers it takes more than 2 million years to achieve complete genetic incompatibility between species. The various prehistoric human groups may therefore have enjoyed connections despite their anatomical and behavioral differences.
Fred Smith, chair of the Department of Sociology and Anthropology at Illinois State University, told Discovery News that Roksandic and her team "have done excellent work on this site and specimen." Smith, however, questions the possibility that the remains are of a new human species, since he wonders if "they are actually older than the current dating suggests. Furthermore, there is a wide range of variation within Neanderthals, so it is not impossible that the Mala Balanica mandible is part of that variation." Such questions may be answered in the future, as Mihailovic hopes future excavations will take place in Greece, Romania, Bulgaria and other parts of the Balkans. Over the past 10 years he and his colleagues have identified more than 100 caves with potential Paleolithic sediments in Serbia and Montenegro alone.
In recent months, scientists have described a new layer in the cornea of the human eye and a long-overlooked ligament in the knee.
In our modern age of imaging and other advanced medical technologies, how is it possible that we still don’t know everything there is to know about our anatomy?
Despite a long history of fascination with the human body, experts said, holes continue to exist in our knowledge because we are enormously complex creatures. What’s more, there's a lot of variation from one person to the next. Reality is a far cry from the clear and colorful pictures in anatomy textbooks.
As medical students begin the reverent work of cadaver dissection, the complexities can be overwhelming.
“When students open up the body for the first time, it’s really hard. It’s really confusing,” said Daniel Schmitt, an evolutionary anthropologist and course director for human gross anatomy at Duke University in Durham, N.C.
“It’s like getting up close to a pointillist painting where you just see dots,” he said. “It’s like going to a new city, a new country, a new world. They just haven’t anticipated what it’s going to be like. It’s beautiful, but the first reaction of many students is: ‘It’s too hard. I can’t do this.’”
Gradually, Schmitt said, rules and patterns emerge. As doctors become experts, they learn where to look for structures that tend to appear in the same general areas from one person to the next.
But even when surgeons develop intricate knowledge about specific parts of the body, they come to expect the unexpected. There is a muscle in the arm called the palmaris longus, for example, that is absent in about 15 percent of people. Some people have the muscle in one arm but not the other.
Surgeons routinely have to make decisions on the fly when they find that someone’s veins or nerves take unexpected paths.
“Human variation is remarkable,” Schmitt said. “Everyone is different.”
Belgian knee surgeon Steven Claes, of the University of Leuven, has long been confronted on a daily basis by a puzzling problem. After undergoing surgery on torn ACLs, one of the four major ligaments of the knee, many patients are never able to return to their original level of sports performance. In those cases, patients tend to suffer from a kind of unstable buckling of the knee known as rotational laxity.
Convinced they must be missing something despite years of refining their techniques, Claes and colleagues decided to focus on the outside of the knee, which basic biomechanical thinking would suggest was the source of rotational control. In a paper written by a French surgeon in 1879, the researchers found a brief mention of a fibrous band on outside of the knee joint that undergoes extreme amounts of tension when the knee rotates.
And even though the band had been discussed several times since, no one had published photographs or described it in detail. So Claes and his team undertook a painstaking series of dissections on the knees of 41 cadavers. In 40 of the knees, they reported in the Journal of Anatomy, the researchers found a distinct, two-inch long structure they call the anterolateral ligament (ALL).
The new findings suggest that the ALL is likely to be an important target for improving results of ACL surgeries.
One reason that surgeons have likely failed to notice the ALL for so long is that arthroscopic procedures prevent a global and detailed look at the joint, Claes said. But there may also be a tendency for doctors to see only what they’re looking for.
“If your teachers tell you, ‘This is the anatomy,’ and you study it in textbooks and then you go back to the cadaver, you will try to find the structures you have studied,” Claes said. “That’s already difficult enough as a student. If you could see a laboratory dissection, you would see the difference between the drawings and the real-life situation. It’s just another world. No one goes in to find structures.” As researchers continue to refine their studies of human anatomy, Schmitt said, they are bound to discover even more nuances. Discoveries will come from both dissections like the knee study and from high-tech imaging, which turned up a previously unknown layer of the cornea earlier this year.
The brain and nervous system are perhaps the largest frontiers, as scientists still have a lot to learn about where nerves run and how the brain functions on a micro-level.
“That’s where we’re going to make discoveries in the next 50 years,” Schmitt said, “strongly and consistently.”