Anthropologists have long puzzled over why Native Americans don't look more like their ancient ancestors. The ancient skulls are larger, their faces are narrower and more forward-projecting, and more closely resemble native peoples of Africa, Australia, and the southern Pacific Rim than their supposed American descendants.
     In 2007, a team led by archaeologist James Chatters found a human skeleton between 12,000 and 13,000 years old matching that description, along with those of extinct sabre-toothed cats, giant ground sloths, and other Pleistocene animals.
     Called 'Naia' by her discoverers, the skeleton belonged to a teenage girl who fell to her death inside a cave on Mexico's Yucatán Peninsula, which divers named Hoyo Negro, or 'Black Hole'.
     Reporting on the find, Deborah Bolnick, an anthropological geneticist at the University of Texas, and one of the study's co-authors, said: "This is the first time that we have genetic data from a skeleton that exhibits these distinctive skull and facial features."
     The find complements the recent genomic sequencing of the 12,600-year-old remains of an infant found at the Anzick Clovis site in Montana, which also shares ancestry with Native Americans.
     Michael Waters, director of the Center for the Study of First Americans at Texas A&M University, said: "Now we've got two specimens, both from a common ancestor that came from Asia. Their differences have to be a result of evolutionary change."
     "We know there's a tremendous variation in physical form, and the sample of crania we have from that time period is so tiny," said David Meltzer of Southern Methodist University, Dallas, Texas. "We've got to be really careful about drawing conclusions based on relatively small samples. That's true for the skeletal anatomy, and it's true for the genetic record as well."
     According to Chatters, the retention of some juvenile traits can be seen in populations across the Northern Hemisphere between the late Pleistocene and modern times. "You start seeing these more domestic forms when females have more control over the food supply, when they're not so dependent on aggressive men."

Edited from PhysOrg, National Geographic News (15 May 2014)