Year in review: Old humans reveal secrets

3

Scientists probed the complete genetic secrets of an unprecedented number of ancient humans this year, revealing insights into how people, ideas and disease spread around the world.

Researchers have gotten so good at working with ancient scraps of DNA that, this fall, they unveiled the entire genetic makeup of a man who lived in Siberia near Ust’-Ishim about 45,000 years ago (SN: 11/29/14, p. 8).

The ancient Siberian’s bones are the oldest modern human remains found outside Africa. Two weeks after the details of Ust’-Ishim man’s genome were reported, other scientists revealed DNA from a more than 36,000-year-old skeleton, known as Kostenki 14, from western Russia.

Ust’-Ishim man is related to East Asians and ancient European hunter-gatherers; the younger Kostenki 14 man is related to western Eurasians and the ancient hunter-gatherers. Both men’s DNA may help pinpoint when eastern and western Eurasians went their separate ways.

These and other ancient remains are revealing that early settlers spread out in multiple directions over wide swaths of Europe and Asia into Siberia. Interbreeding and migration occurred repeatedly — maybe even continually — forming what was essentially one large population of Stone Age people.

Also written in the men’s DNA are accounts of interbreeding between modern humans and Neandertals. Based on the length of DNA segments shared between the Ust’-Ishim man and Neandertals (whose genome was reconstructed in 2010), researchers estimated that the two hominid species mostly interbred between 50,000 and 60,000 years ago. Analysis of the Kostenki 14 man’s Neandertal ancestry similarly estimates the hookup at about 54,000 years ago.

Researchers are also reading other new versions of old stories in ancient DNA. The prehistories of Europe, Siberia and the Americas in particular are undergoing revision. Scientists can glean information from DNA that old bones or relics don’t reveal, such as what people looked like and their genetic relationship to people who came before or after them.

Hunter-gatherers who first settled Europe may have had dark skin far longer than previously thought, for instance (SN Online: 5/2/14; SN: 2/22/14, p. 14). And blue eyes may have evolved before light skin, researchers learned from examining the DNA of a 7,000-year-old Spaniard (SN: 2/22/14, p. 14).

Ancient DNA may also help settle a debate about how agriculture spread (SN: 5/17/14, p. 26; SN Online: 4/24/14). Hunter-gatherers were replaced and assimilated into farming populations as migrants spread agriculture, DNA isolated from 5,000- to 7,500-year-old skeletons in Sweden showed. That finding suggests that agriculture was not a viral idea but rather a cottage industry that moved along with people.

Ancestry has also come under genetic scrutiny. Ancient Siberians were discovered to be ancestors of both Europeans (SN: 5/17/14, p. 26) and native groups in North and South America (see Page 29). Even standard history may need a little rewriting in light of DNA evidence: Anglo-Saxons may have imposed language and culture on Briton but didn’t leave much of a genetic legacy, new research hints (SN: 11/29/14, p. 13).

Plant DNA pulled from permafrost up to 50,000 years old suggests that shifts in vegetation contributed to the demise of Ice Age mammals, such as woolly mammoths (SN: 3/22/14, p. 13). Overhunting has often been blamed for the extinction of large animals, but the study suggests that the real story of Ice Age extinctions was far more complicated.

Still, humans aren’t off the hook. A genetic analysis found that giant flightless birds called moa thrived in New Zealand before people arrived (SN: 4/19/14, p. 15). DNA from long-dead chickens hinted that early Polynesians may not have reached South America (SN Online: 3/19/14). But modern Easter Islanders and Native Americans share genetic ties, indicating that Polynesians and indigenous South Americans mated between 1280 and 1495 (SN: 11/29/14, p. 12). Ancient DNA from Pacific Islanders and South Americans may clarify the matter.

Whether or not Polynesians colonized South America before Columbus set sail, seals seem to have brought tuberculosis there long before Europeans arrived (SN: 9/20/14, p. 16).