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Raghavan et al., Science (2015)
Raghavan et al., Science (2015)

The First People Entered the Americas 23,000 Years Ago, Study Finds

Raghavan et al., Science (2015)
Raghavan et al., Science (2015)

People arrived in the Americas relatively later than on other continents. The oldest evidence for anatomically modern humans in Asia comes from bones that are at least 46,000 years old, for instance, while the oldest archaeological evidence for people in the Americas, found in Chile, is only 15,000 years old

Two new scientific papers provide new information about how people migrated to North and South America thousands of years ago, one that indicates that humans migrated in a single wave from Siberia 23,000 years ago, and one that finds evidence for a genetic link between some Amazonian peoples and indigenous Australians and islanders from southeast Asia. 

In a study published in the journal Science, an international team of researchers led by the University of Copenhagen analyzed the DNA of contemporary Native American and Siberian populations and compared their genetics to genetic data taken from ancient Native American DNA dating back 200 to 6000 years ago, including some from the ancient Washington state resident known as Kennewick Man.

They determined that all Native American populations descended from a single migration wave across the Bering Strait and into the Americas as long as 23,000 years ago, though there was a later wave of migration that established Eskimo and Inuit populations in the Arctic. The genetic split between North and South American populations might have occurred around 13,000 years ago. 

"Some of the most important questions people ask are: Who are we? Where did we come from?" study co-author Michael Crawford, an anthropologist at the University of Kansas, says. "Now, thanks to genetic analysis, the picture is clearer for Native Americans: They came from Siberia."

However, the picture may not be quite crystal clear. “At the same time, we see surprises including genetic signals of East Asians and Australo-Melanesians, presumably coming in after the first migration wave,” study author Eske Willerslev of the University of Copenhagen explains in a press release. Those genetic signals are discussed in a separate study published in Nature this week, which claims genetic evidence for a link between some indigenous Amazonian populations and people from southeast Asia and Australia. The analysis, led by Harvard Medical School geneticists, shows that two groups who currently live in the Amazon are more closely related to indigenous populations of modern Australia, New Guinea, and the Andaman Islands than to contemporary Eurasian or Native American populations. 

The two groups have diverging hypotheses about how this Australian DNA got mixed into American populations. The University of Copenhagen-led research points to Australasian ancestors arriving in the Americas less than 9000 years ago, while the Harvard group argues that the Australasian ancestors of the Amazonians came to America along with the first migration, but that this Population Y was later wiped out and replaced by other genetic populations. 

It’ll take a lot more research to sort out the mystery of the strange Australian genes in South America, but at least now we know that humans have been wandering around the Americas for some 20,000 years. 

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Mark Golitko
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Stones, Bones, and Wrecks
6000-Year-Old Skull Might Belong to World's Oldest Tsunami Victim
Scientists speak to residents in Aitape.
Scientists speak to residents in Aitape.
Mark Golitko

Tsunamis and other natural disasters have taken a deadly toll on human populations for millennia, and now we may have the oldest example of that truth yet. An international team of anthropologists and environmental researchers recently analyzed a cracked skull that belonged to a person who likely died in a tsunami some 6000 years ago. They detail their find in a new study published in PLOS One.

The partial skull in question, known as the Aitape skull, was found in Papua New Guinea in 1929 during a geological survey by an Australian scientist named Paul Hossfield. It has since been dated to the mid-Holocene epoch, or around 6000 years ago.

For the current study, the scientists returned to the site of the 1929 discovery to sample and analyze the sediment there to find out more about what might have killed the person millennia ago. They had only Hossfield's basic field descriptions to go on, but University of Notre Dame anthropologist Mark Golitko, one of the study’s authors, says that based on those descriptions, they think they were able to sample within 100 yards or so of the skull's original location.

The top of a brown cracked skull against a pink background
Arthur Durband

Based on the grain size, chemical signature, and marine microalgae found within the sediment samples, they were able to determine that around the time that the skull was buried, the area was inundated with water, probably from a tsunami. At that time, the site, located near the present-day town of Aitape, would have been just along the shoreline. Aitape was also the site of a devastating tsunami in 1998, and the Holocene sediments resembled the ones associated with that disaster.

It's possible that the skull was buried before the tsunami hit, and the grave was ripped apart by the waters and the rest of the bones scattered. However, during the powerful 1998 tsunami that killed more than 2100 people in Papua New Guinea, bodies buried in modern cemeteries were not uprooted even as the sediment above them washed away, making it more likely that the ancient skull belonged to someone killed in the disaster.

The new analysis has "made us realize that human populations in this area have been affected by these massive inundations for thousands of years," study co-author James Goff of the University of New South Wales said in a press statement. "Given the evidence we have in hand, we are more convinced than before that this person was either violently killed by a tsunami, or had their grave ripped open by one."

Field Museum anthropologist John Terrell, another co-author of the study, said, "If we are right about how this person had died thousands of years ago, we have dramatic proof that living by the sea isn't always a life of beautiful golden sunsets and great surfing conditions."

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6 Pioneering Facts About Mary Leakey

Fossil bones and the earliest footprints of our human ancestors are just a few of Mary Leakey’s groundbreaking discoveries. Get to know the legendary paleoanthropologist, and learn how her serendipitous finds forever altered scientists’ understanding of human origins.

1. MARY LEAKEY WAS A BORN EXPLORER.

Mary Leakey (1913-1996), née Mary Nicol, was destined to be an explorer: Her father, Erskine Nicol, was a landscape painter, and the family traveled extensively through France, Italy, and Switzerland. While staying in a commune in southern France, 12-year-old Mary became interested in archaeology after meeting Elie Peyrony, a French prehistorian excavating a cave. Mary dug through his tiny finds—which included fine points, scrapers, and flint blades—and sorted them into an amateur classification system.

2. FOSSIL HUNTING WAS IN HER BLOOD ...

Leakey’s parents were artists, but hunting for fossils was part of her heritage: Her maternal great-great-grandfather was John Frere, an 18th-century English government official and antiquarian who’s credited with first recognizing Stone Age flint objects as early weapons and tools.

3. ... BUT SHE WASN'T A GREAT STUDENT.

Leakey was intelligent, but she also had a rebellious streak. As a teen, she was expelled from several Roman Catholic convent schools—once for intentionally creating an explosion in a chemistry lab. Figuring she wasn’t cut out for a classroom, Leakey never finished high school, and decided to pursue independent studies in art, geology, and archaeology at the University of London instead. (“I had never passed a single school exam, and clearly never would,” the scientist later wrote in her 1986 autobiography Disclosing the Past.)

4. LEAKEY WAS AN ARTIST WHEN SHE MET HER FUTURE HUSBAND AND RESEARCH PARTNER, LOUIS LEAKEY.

Mary Leakey—who inherited her father’s artistic skills— ended up working as an illustrator for archaeological digs. An archaeologist introduced her to Cambridge University paleontologist Louis Leakey, who needed an illustrator for his book Adam’s Ancestors (1934). The two became lovers, but their union resulted in scandal, as Leakey was still married at the time. The couple married in 1936, after Leakey divorced his first wife.

5. MARY LEAKEY'S FIRST BIG DISCOVERY WAS PROCONSUL AFRICANUS.

Mary Leakey's first major discovery came in 1948 when she found a fossil skull fragment of Proconsul africanus, an ancestor of apes and humans, which later diverged into two separate species. The fossil was thought to be more than 18 million years old.

6. ANOTHER ONE OF MARY LEAKEY'S FAMOUS FINDS CAME COURTESY OF ELEPHANT POOP.

In 1978, Leakey was on an expedition in Laetoli, in Tanzania, when members of her camp engaged in a spirited elephant dung fight. A scientist fell down, and he noticed strange indentations on the ground that had been recently exposed by erosion. They turned out to be tracks made around 3.7 million years prior, from animals that had walked over damp volcanic ash. Examining these prints took several years, but the team's efforts paid off when Leakey noted that one of the prints seemed to be made by a hominin. This discovery showed that early humans began walking upright long before scientists thought they had.

Additional source: Ancestral Passions: The Leakey Family and the Quest for Humankind's Beginnings, Virginia Morell

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