Separation Between Neanderthal and Homo Sapiens Might Have Occurred 500,000 Years Earlier, DNA from Teeth Suggests

ScienceDaily (June 23, 2010) — The separation of Neanderthal and Homo sapiens might have occurred at least one million years ago, more than 500.000 years earlier than previously believed, according to new DNA-based analyses.

A doctoral thesis conducted at the National Center for Research on Human Evolution (Centro Nacional de Investigación sobre la Evolución Humana), associated with the University of Granada, analyzed the teeth of almost all species of hominids that have existed during the past 4 million years. Quantitative methods were employed, and they managed to identify Neanderthal features in ancient European populations.

The main purpose of this research, whose author is Aida Gómez Robles, was to reconstruct the history of evolution of the human species using the information provided by the teeth, which are the most numerous and best preserved remains of the fossil record. To this purpose, a large sample of dental fossils from different sites in Africa, Asia and Europe was analyzed. The morphological differences of each dental class were assessed and the ability of each tooth to identify the species to which its owner belonged was analyzed.

The researcher concluded that it is possible to correctly determine the species to which an isolated tooth belonged with a success rate ranging from 60% to 80%. Although these values are not very high, they increase as different dental classes from the same individual are added. That means that if several teeth from the same individual are analyzed, the probability of correctly identifying the species can reach 100%.

Aida Gómez Robles explains that, from all the species of hominids currently known, "none of them has a probability higher than 5% to be the common ancestor of Neanderthals and Homo sapiens. Therefore, the common ancestor of this lineage is likely to have not been discovered yet."

Computer Simulation

What is innovative about this study is that computer simulation was employed to observe the effects of environmental changes on morphology of the teeth. Similar studies had been conducted on the evolution and development of different groups of mammals, but never on human evolution.

Additionally, the research conducted at CENIEH and at the University of Granada is pioneering -- together with recent studies based on the shape of the skull -- in using mathematical methods to make an estimation of the morphology of the teeth of common ancestors in the evolutionary tree of the human species. "However, in this study, only dental morphology was analyzed. The same methodology can be used to rebuild other parts of the skeleton of that species, which would provide other models that would serve as a reference for future comparative studies of new fossil finds."

To carry out this study, Gómez Robles employed fossils from a number of archaeological-paleontological sites, such as that of the Gran Colina and the Sima de los Huesos, located in Atapuerca range (Burgos, Spain), and the site of Dmanisi in the Republic of Georgia. She also studied different fossil collections by visiting international institutions as the National Museum of Georgia, the Institute of Human Paleontology and the Museum of Mankind in Paris, the European Research Centre Tautavel (France), the Senckenberg Institute Frankfurt, the Museum of Natural History in Berlin, the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and the Museum of Natural History in New York and Cleveland.

The results of this research were disclosed in two articles published in Journal of Human Evolution (2007 and 2008), and they will also be thoroughly presented within a few months.

http://www.sciencedaily.com/releases/2010/06/100623104436.htm

More Than Skin Deep, Tanning Product of Sun's Rays

ScienceDaily (June 22, 2010) — People who remain pale and never tan can blame their distant ancestors for choosing to live in the northern reaches of the globe and those who easily achieve a deep tan can thank their ancestors for living in the subtropical latitudes, according to Penn State anthropologists.



People who remain pale and never tan can blame their distant ancestors for choosing to live in the northern reaches of the globe and those who easily achieve a deep tan can thank their ancestors for living in the subtropical latitudes, according to Penn State anthropologists. (Credit: iStockphoto/Yuliyan Velchev)

"The variation of ultraviolet radiation, especially in the middle and high latitudes is great," said Nina Jablonski, professor of anthropology and chair of Penn State's anthropology department. "Tanning has evolved multiple times around the world as a mechanism to partly protect humans from harmful effects of ultraviolet radiation."

Jablonski, working with George Chaplin, senior research associate in anthropology and an expert in geographic information systems, looked at the way the sun illuminates different parts of the Earth. They looked at levels and angles of incidence of both ultraviolet A and B radiation at various latitudes. Ultraviolet B radiation is much more variable than ultraviolet A as latitude increases due to atmospheric scattering of the light and absorption by oxygen.

Ultraviolet B radiation produces vitamin D in human skin. Ultraviolet radiation can, however, destroy folate. Folate is important for the rapid growth of cells, especially during pregnancy where its deficiency can cause neural tube defects.

"What we now recognize is that some of the medical problems seen in darkly pigmented people may be linked at some level to vitamin D deficiency," said Jablonski. "Things like certain types of cancer in darkly pigmented people and in people who use a lot of sunscreen or always stay inside could be partly related to vitamin D deficiency."

Scientists have understood for years that evolutionary selection of skin pigmentation was caused by the sun. As human ancestors gradually lost their pelts to allow evaporative cooling through sweating, their naked skin was directly exposed to sunlight. In the tropics, where human ancestors evolved and where both ultraviolet radiations are high throughout the year, natural selection created darkly pigmented individuals to protect against the sun.

"Past arguments about the selective value of dark pigmentation focused on the protective effects of melanin against sunburn, skin cancer, and overproduction of vitamin D. These factors can no longer be considered significant selective pressures," the Jablonski and Chaplin report in a recent issue of the Proceedings of the National Academy of Sciences.

Sunburn and most skin cancers do not alter an individual's ability to procreate, so they are not selection factors. The human body also has a mechanism to prevent overproduction of vitamin D.

Previously, the researchers concluded that dark skin pigmentation in the tropics protects people from folate destruction by ultraviolet B, but, because levels of ultraviolet B are high year round, the skin can still allow enough in to manufacture vitamin D.

As humans moved out of Africa, they moved into the subtropics and eventually inhabited areas up to the Arctic Circle. Ultraviolet radiation in these areas is neither consistent nor strong. North or south of 46 degrees latitude, which includes all of Canada, Russia, Scandinavia, Western Europe and Mongolia, there is insufficient ultraviolet B through most of the year to produce vitamin D. Populations in these areas evolved to have little skin pigmentation.

In the latitudes between 23 and 46 degrees, an area that encompasses North Africa, South America, the Mediterranean and most of China, ultraviolet B radiation is much more variable. Heavily pigmented skin in the winter would block the development of vitamin D, and lightly pigmented skin during the summer would allow destruction of folate.

"We actually demonstrate that in those middle latitudes where highly fluctuating levels of ultraviolet radiation occur throughout the year, tanning has evolved multiple times as a mechanism to partly protect humans from harmful effect of the sun," said Jablonski.

The tanning process evolved for humans who by and large were naked all the time. As the ultraviolet B radiation began to increase in the early spring, the skin would begin to gradually darken. As the sun became stronger, the tan became deeper. During the winter, as ultraviolet B waned, so did the tan, allowing Vitamin D production and protecting folate.

The researchers note that the ability to tan developed in a wide variety of peoples and while the outcome, tanablity, is the same, the underlying genetic mechanisms are not necessarily identical. They also note that depigmentated skin also developed at least three times through different genetic mechanisms.

Implications for today focus on the fact that depigmented people now live in tropical and subtropical areas where besides getting sunburned they run the risk of losing folate. Highly pigmented people live in higher latitudes where they may become vitamin D deficient, especially if they use sunscreens.

"It is a conspiracy of modernity," said Jablonski. "The rapidity at which we can move long distances and live far away from our ancestral homelands. The fact that we can live and work indoors. All this has happened within the last 500 years and especially within the last 200 years."

http://www.sciencedaily.com/releases/2010/06/100621125137.htm

3.6 Million-Year-Old Relative of 'Lucy' Discovered: Early Hominid Skeleton Confirms Human-Like Walking Is Ancient

ScienceDaily (June 21, 2010) — Meet "Lucy's" Great-Grandfather. Cleveland Museum of Natural History Curator and Head of Physical Anthropology Dr. Yohnannes Haile-Selassie led an international team that discovered and analyzed a 3.6 million-year-old partial skeleton found in Ethiopia. The early hominid is 400,000 years older than the famous "Lucy" skeleton and is significantly larger in size. Research on the new specimen reveals that advanced human-like, upright walking occurred much earlier in the evolutionary timeline than previously thought.

Haile-Selassie is the first author of the initial analysis of the specimen, which will be published in the online early edition of the Proceedings of the National Academy of Sciences during the week of June 21, 2010.

The partial skeleton belongs to "Lucy's" species, Australopithecus afarensis. It was found in the Woranso-Mille area of Ethiopia's Afar region by a team led by Haile-Selassie that excavated of the skeleton over five years following the discovery in 2005 of the lower arm bone. The team recovered the most complete clavicle and one of the most complete shoulder blades ever found in the human fossil record. A significant portion of the rib cage was also found.

The specimen was nicknamed "Kadanuumuu" (kah-dah-nuu-muu) by the authors. This means "big man" in the Afar language and reflects its large size. The male hominid stood between 5 to 5 ½ feet tall, while "Lucy" stood only 3 ½ feet tall.

"This individual was fully bipedal and had the ability to walk almost like modern humans," said Haile-Selassie. "As a result of this discovery, we can now confidently say that 'Lucy' and her relatives were almost as proficient walking on two legs as we are, and that the elongation of our legs came earlier in our evolution that previously thought."

He explained, "All of our understanding of Australopithecus afarenis' locomotion was dependent on 'Lucy.' Because she was an exceptionally small female with absolutely short legs, this gave some researchers the impression that she was not fully adapted to upright walking. This new skeleton falsifies that impression because if 'Lucy's' frame had been as large as this specimen, her legs would also have been proportionally longer."

Kent State University Professor Dr. C. Owen Lovejoy was a co-author of the research and helped analyze the skeleton. When comparing it to "Lucy," Lovejoy said, "They both have pelves, a complete lower limb bone and elements of the forelimb, vertebral column and thorax. However, the new specimen has more complete ribs and a nearly complete scapula, which tells us much more about body form in Australopithecus afarensis than 'Lucy' was able to alone."

Authors of the research include Cleveland scientists Dr. Bruce Latimer, interim director of the Center for Human Origins of the Institute for the Science of Origins at Case Western Reserve University, and Dr. Beverly Saylor, associate professor of geological sciences at Case Western Reserve University. Other co-authors are from Addis Ababa University in Ethiopia, Berkeley Geochronology Center and Stanford University.

Australopithecus afarenis is the best-known direct early human ancestor. Until now, the only partial skeleton assigned to this species was "Lucy," a 3.2 million-year-old female individual, which was discovered in 1974 by a team led by then Museum curator Dr. Donald Johanson.

The analysis of "Kadanuumuu" indicates that the shoulder and rib cage of this species were different from those of chimpanzees. "These findings further confirm what we concluded from the 'Ardi' specimen -- that chimpanzees have undergone a great deal of specialized evolution since we shared a last common ancestor with them," said Lovejoy.

"Ardi," or Ardipithecus ramidus is a 4.4 milion-year-old hominid species that was unveiled in October 2009 by a team that included Haile-Selassie, Lovejoy, and Museum scientists and associate researchers Dr. Linda Spurlock, Dr. Bruce Latimer and Dr. Scott Simpson. "Ardi" was named by the journal Science as breakthrough discovery of the year. Click here to find out more about "Ardi."

http://www.sciencedaily.com/releases/2010/06/100621151119.htm