Skulls reveals that ancient Americans didn’t mix with neighbours

Human Evolution

It’s a real head-scratcher. The shapes of human skulls from a narrow strip in Mexico reveal that first arrivals to the Americas may have kept to themselves, even when there were no geographical barriers that would have prevented them mixing.

Genetic studies have begun to unravel the complex story of the earliest American settlers, but archaeological studies can provide important details too – particularly the careful study of human skull shape. This is influenced by someone’s genetic history: when two populations become isolated from each other and can no longer interbreed, they each begin to develop unique genetic signatures – and skull shapes.

Mark Hubbe and Brianne Herrera at the Ohio State University in Columbus and their colleagues took detailed measurements from a series of 800 to 500-year-old skulls unearthed in three regions of Mexico. They then looked at equivalent measurements from skulls found at a number of sites across North and South America, East Asia and Australasia and analysed how skull shape varied with location.

Skulls from two of the Mexican regions – Sonora and Tlanepantla – clustered together in the shape analysis. But skulls from the third region, Michoacán, were different. The variation was on a scale normally seen between two populations that have been separated for millennia, often because they have settled in regions that are thousands of kilometres apart. Yet the distance between Michoacán and Tlanepantla is under 300 kilometres.

It’s an astonishing discovery, says Hubbe. Mexico was first inhabited at least 10,000 years ago, and the founding populations may well have had different genetic histories before they settled in the area. Crucially, the populations seem to have been so reluctant to interbreed that those genetic differences were still apparent just 500 years ago. “For whatever reason, these differences have been maintained for thousands of years,” says Hubbe.

Mexico lacks obvious geographical features that could have kept people apart – but formidable cultural and language barriers might have existed, says Hubbe.

“When it comes to population history, a whole host of scenarios are possible,” says Noreen von Cramon-Taubadel of the University at Buffalo, New York. “We see instances even in modern populations where neighbouring groups live in close geographic contact yet do not mix extensively in terms of marriage.”

Skull and other remains at Brazilian burial site

Hubbe and von Cramon-Taubadel collaborated on a second study, which involved analysing another set of early American skulls (pictured top and above). These came from Lagoa Santa in eastern Brazil and date back 10,000 to 7000 years, not long after South America was first inhabited.

“The Lagoa Santa material is unique in the entire New World,” says André Strauss at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was also involved in the work. “It presents abundant, well-preserved, old skeletons with reliable associated archaeological context.”

The researchers discovered that these earliest South Americans – the “Palaeoamericans” – had skull shapes that are distinctly different from those of most indigenous South American populations alive today.

“The differences between the Palaeoamericans and today’s South Americans are so large that they cannot simply have appeared in 10,000 years,” says Hubbe.

In other words, the Palaeoamericans cannot simply have evolved into today’s indigenous South Americans. Instead, the researchers estimate that the two populations split apart from a shared ancestral population at least 20,000 years ago, offering a much larger time window for the two groups to develop distinct skull features.

Because the consensus is that the Americas were not inhabited 20,000 years ago, this conclusion implies that South America may have been colonised in at least two distinct waves – one represented by the ancient people at Lagoa Santa and another by today’s indigenous South American populations.

This goes against the general assumption that South America was initially colonised in just one wave, before the Europeans arrived. It isn’t the first evidence that the South American story is more complicated, though – a 2015 study also raised the possibility of multiple colonisation waves by uncovering a genetic link between some of today’s Amazonian populations and indigenous groups in Australia.

“It is great to see this new analysis of morphological data,” says Pontus Skoglund at Harvard Medical School, an author on the 2015 study. “It reiterates that there is something interesting about the peopling of the Americas that we don’t quite understand yet.”

Journal reference: American Journal of Physical Anthropology, DOI: 10.1002/ajpa.23186

Journal reference: Science Advances, DOI: 10.1126/sciadv.1602289

Article Reprint from New Scientist

Palaeoprimatologist Elwyn Simons Has Died

Human Evolution

On the 6th of March 2016, the accomplished palaeoprimatologist Elwyn Simons passed away in his sleep at the age of 85. It is difficult to overstate this man’s contribution to our understanding of the evolution of Primates. He directed over 90 palaeontological expeditions between 1961 and 2012 which produced over 300 books and peer-reviewed journal articles. As Gregg Gunnell of the Duke Lemur Center noted “I don’t know of anyone in the last half century who has influenced the field as much as he has”.

Elwyn LaVerne Simons was born on the 14th of July 1930 in Lawrence City, Kansas. From William Marsh Rice University, Houstan, Texas, he earned his bachelors degree before moving onto Princeton and Oxford for his doctoral degrees. Prior to joining Duke University in North Carolina, he spent 17 years at Yale University as a professor.

You cannot talk about Elwyn Simons and not mention his work in Egypt. For more than 40 years, Simons and co-director Prithijit Charath organised expeditions to a low basin of desert, south west of Cairo – The Fayum Depression. In Passionate Minds: The Inner World of ScientistsSimons had this to say:

“It’s fun to find fossils because you never know what your’re going to find and there’s always a chance that you’ll find something quite unusual, and that kind of excitement makes it sort of like a treasure hunt”

Fayum Depression

Friderun Ankel-Simons of the Duke Primate Center, recalled the many years of working with her husband. The expeditions were very challenging with all obstacles put in their way from vehicles getting stuck in the sand or mud and running out of diesel on many different occassions. These were sharply contrasted with the good times out in the field, camping beneath the stars in the desert, hearing the desert fox calling or arguing lemurs nearby. He was a very active man, depriving himself of sleep countless times. Daniel Gebo of the Northern Illinois University remembers one time he was conversing with Elywn and out of the blue he said “I have to take a nap NOW” and would simply fall asleep, leaving Daniel wondering what to do about what they were talking about.

Elwyn had the power to captivate an audience, recalled John Fleagle of Stony Brook University. He was an expert storyteller, a model for people who specialise in scientific communication.

Famously, Simons discovered the fossilised remains of an ancient genus of primate – Aegyptopithecus this primate lived in Egypt between 35 to 33 million years ago. It was probably about the same size as South America’s Howler Monkey and remains one of the best known extinct primates from that time. One afternoon, while at an anthropology conference, Simons asked if he could use an empty chair beside a group of anthropologists. “Actually, a friend of ours is just getting a drink”, responded one member of the group. Simons proceed to lift up the chair and say “Yes? Well I discovered Aegyptopithecus

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After joining Duke University in 1977, Simons first task was to take an ailing Primate Center and make it an essential breeding programme for wild Lemurs. With populations dwindling on Madagascar, the Malagasy government permitted Simons to capture wild lemurs, relocating them to North Carolina, where he could diversify the gene pool of species. This in his own word created “a second line of defense against extinction”. His passion for the work he was doing, was plain to see in the cradling and hand-feeding of premature newborn lemurs. Thanks to Simons, Duke Primate Center now has the most diverse collection of captive lemurs ouside of Madagascar with hundred of individuals representing over 20 species. The breeding programme allowed Simons to reintroduce lemurs to the wild.

Elywn Simons will forever be remembered for shedding light on primate evolution in the Oligocene of Egypt and helping prevent the extinction of Madagascar’s Lemurs. Simons is survived by his wife of more than 40 years, Friderun Ankel-Simons; a brother, Herbert Simons; three children, D. Brenton Simons, Cornelia Seiffert and Verne Simons; and two grandchildren, Eleanor and William Simons.

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Right: Elwyn Simons cares for an Aye-Aye. Left: An Aye-Aye scoping out its next meal.

Do check out the “Adopt A Lemur” Project, which helps support the great work done at the Duke Primate Center.