Ötzi’s Neandertal ancestry
A 5,300-year-old man found sticking out of an Alpine glacier in 1991 possessed more genes in common with Neandertals than Europeans today do. The man’s Neandertal heritage is a preliminary sign that Stone Age interbreeding occurred more frequently than many scientists assume. Two researchers determined that the previously analyzed genome of Ötzi the Tyrolean Iceman (SN: 3/24/12, p. 5) included roughly 4 to 4.5 percent Neandertal genes. Modern Europeans’ genetic library includes an average of 2.5 percent Neandertal genes.
Human groups that migrated into Europe after 5,000 years ago mated with continental natives and diluted traces of Neandertal genetic ancestry in Ötzi, proposed Aaron Sams of Cornell University on April 12.
It’s difficult to estimate precisely how many genes in the Iceman or in living people had roots in Neandertals, said study coauthor John Hawks of the University of Wisconsin – Madison, because ancient populations ancestral to both humans and Neandertals may have passed along some genes common to both species.
Organic material may be oldest example of human skin
The earliest preserved swatch of hominid skin may have been found by discoverers of South African fossils assigned to a nearly 2-million-year-old species called Australopithecus sediba, a possible precursor of the Homo genus. Reddish brown material on the skull of an A. sediba boy shows provocative similarities to human skin, Rachelle Keeling of the University of the Witwatersrand in Johannesburg reported on April 11.
Microscopic analyses of the substance revealed irregular lines resembling blood vessels, as well as depressions characteristic of fat pockets and hair follicles. Chemical tests confirmed that the stuff is organic and has a molecular structure like that previously found in the skin of mummified human bodies.
A. sediba individuals fell into an underground cave where their bodies were quickly covered by soil in a dry place free of predators, making the preservation of skin possible, Keeling said. Further tests are planned to verify that the ancient boy is the world’s oldest skin head.
First hominid’s rewired brain
A computer-generated cast of the inner surface of a 7-million-year-old cranium, which bears impressions once made by brain features, suggests that hominid evolution kicked off with big neural changes. The skull, unearthed in Africa in 2001, belongs to Sahelanthropus tchadensis, a species controversially proposed as the earliest known member of the human evolutionary family.
X-rays enabled a research team to see through Sahelanthropus’ rock-filled cranium and reconstruct its brain surface. That 3-D reconstruction of the ancient creature’s brain terrain reveals a hominidlike setup, said Thibaut Bienvenu of the University of Poitiers, France, on April 12. Shapes of the front and back of Sahelanthropus’ brain, as well as the tilt of its brain stem, matched corresponding brain measures for 2- to 4-million-year-old hominids and modern humans.
An upright posture and two-legged gait stimulated neural reworking in Sahelanthropus, Bienvenu speculated, even though the hominid’s brain was about one-quarter the size of people’s brains today.