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Raghavan et al., Science (2015)

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

Original image
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. 

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.


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.


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.


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.)


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.


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.


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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Wikimedia Commons // Public Domain
Stones, Bones, and Wrecks
Researchers Unveil an Unusual New Theory For How Easter Island’s Statues Were Made
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Wikimedia Commons // Public Domain

The Moai statues of Easter Island present one of the world's greatest technical mysteries. The stone heads (actually full bodies) that dot the island in the South Pacific are massive and number in the hundreds, prompting archaeologists to wonder how they got there in the first place. Now, as Newsweek reports, a group of researchers believe they're closer to finding an answer.

European sailors first arrived on Easter Island in 1722 and were greeted by a native population of 1500 to 3000. Along with the residents were 900-odd statues carved from solid rock, meaning there were fewer than four people for every massive monolith.

How was such a thin population able pull off such an impressive feat of architecture? According to researchers from Chile, New Zealand, and the U.S., it's possible they had help. Their new study published in the journal Frontiers in Ecology and Evolution suggests that the statues were carved and erected at a time when Easter Island supported a much larger population. Using data from the island, they estimated just how high the island's numbers may have reached.

Easter Island has the agriculture potential to sustain a maximum population of 17,500, researchers say. This estimate is based on the weather and soil quality of the island, 19 percent of which is capable of growing the sweet potatoes that fed inhabitants. "Despite its almost complete isolation, the inhabitants of Easter Island created a complicated social structure and these amazing works of art before a dramatic change occurred," lead author Cedric Puleston said in a statement.

If the Moai were constructed by a much larger group than the Europeans encountered, that would clear up some of the mystery surrounding the island. But it would also raise more questions. How, for instance, did the population fall so quickly in the few centuries between the statues' construction and first contact with Europeans? One theory is ecocide, which happens when an area is exhausted of its resources faster than it can replenish them.

The mystery of how the towering monoliths were transported across the island after they were built still remains. The indigenous people told Dutch explorers that the Moai walked themselves, an explanation an MIT professor put to the test when he designed a 2000-pound sculpture that could be shimmied long distances. But despite the numerous theories, hard evidence related to the figures' origins remains scarce.

[h/t Newsweek]


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