Scientists May Have Finally Figured Out Why We Have Eyebrows

A Neanderthal skull
A Neanderthal skull
Stephane De Sakutin, AFP/Getty Images

If you look at a pictures of some of the earlier branches of humanity's family tree, like Neanderthals or Homo erectus, you might notice that Homo sapiens got off relatively lightly, eyebrow-wise. Most early hominins had thick, bony brow ridges rather than the smooth brows of modern humans. For years, researchers have been arguing over why those thick ridges existed—and why modern humans evolved tinier brows. A new study suggests that heavy brow ridges had social usefulness that was more important than their physiological function.

Previous research has suggested that thick brow ridges helped connect early hominins' eye sockets with their brain cavities, or protected the skull from the physical stress put on it by chewing jaws, or even helped early hominins take punches to the face.

The new study by University of York researchers, published in the journal Nature Ecology & Evolution, used a digital model of a fossil skull, thought to be between 125,000 and 300,000 years old, of an extinct species called Homo heidelbergensis that evolved sometime between 300,000 and 600,000 years ago in what is now Zambia. The researchers manipulated the model, changing the size of the brow ridge and seeing what happened when they applied different bite pressures. They found that the brow ridge was much bigger than it needed to be if its purpose was just to connect the eye sockets with the brain case, and that it didn't seem to protect the skull from the force of biting.

Instead, the researchers suggest that the brow ridge played a social role. Other primates have similar brow ridges that serve a social purpose rather than a mechanical one, like male mandrills, whose colorful, heavy-browed muzzles serve as dominance displays. Heavy brow ridges may have played a similar role in early human species.

As Homo sapiens evolved, more subtle communication may have taken precedence over the permanent social signal of a giant brow ridge. As foreheads became more vertical, eyebrows could move more freely and subtly, leading to important social signals in modern humans, like expressions of surprise or indignation.

An accompanying analysis in the same journal, by Spanish paleontologist Markus Bastir, cautions that the results of the new study are appealing, but should be taken with a grain of salt. The specimen used for the digital model was missing a mandible, and the researchers subbed in a mandible from a Neanderthal, a related species but still a distinct one from Homo heidelbergensis. This may have altered the analysis of the model and bite stresses. Still, the study provides "exciting prospects for future research," he writes.

Looking to Downsize? You Can Buy a 5-Room DIY Cabin on Amazon for Less Than $33,000

Five rooms of one's own.
Five rooms of one's own.
Allwood/Amazon

If you’ve already mastered DIY houses for birds and dogs, maybe it’s time you built one for yourself.

As Simplemost reports, there are a number of house kits that you can order on Amazon, and the Allwood Avalon Cabin Kit is one of the quaintest—and, at $32,990, most affordable—options. The 540-square-foot structure has enough space for a kitchen, a bathroom, a bedroom, and a sitting room—and there’s an additional 218-square-foot loft with the potential to be the coziest reading nook of all time.

You can opt for three larger rooms if you're willing to skip the kitchen and bathroom.Allwood/Amazon

The construction process might not be a great idea for someone who’s never picked up a hammer, but you don’t need an architectural degree to tackle it. Step-by-step instructions and all materials are included, so it’s a little like a high-level IKEA project. According to the Amazon listing, it takes two adults about a week to complete. Since the Nordic wood walls are reinforced with steel rods, the house can withstand winds up to 120 mph, and you can pay an extra $1000 to upgrade from double-glass windows and doors to triple-glass for added fortification.

Sadly, the cool ceiling lamp is not included.Allwood/Amazon

Though everything you need for the shell of the house comes in the kit, you will need to purchase whatever goes inside it: toilet, shower, sink, stove, insulation, and all other furnishings. You can also customize the blueprint to fit your own plans for the space; maybe, for example, you’re going to use the house as a small event venue, and you’d rather have two or three large, airy rooms and no kitchen or bedroom.

Intrigued? Find out more here.

[h/t Simplemost]

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

Humans First Arrived in North America 30,000 Years Ago, New Studies Suggest

Researcher samples cave sediments for DNA.
Researcher samples cave sediments for DNA.
Devlin A. Gandy

People occupied North America by roughly 11,000 BCE, but the exact timeline of how early humans first arrived on the continent is contested. Two new studies suggest that humans were living in North America as far back as 30,000 years ago—preceding some earlier estimates by more than 15,000 years.

According to the traditional narrative, the first North Americans were big game hunters who crossed a land bridge connecting Asia to North America around 13,000 years ago. They left behind distinct, fluted arrowheads and bone and ivory tools that were dubbed “Clovis” tools. “This narrative, known as ‘Clovis-first,’ was widely accepted for most of the 20th century until new archaeological evidence showed that humans were present in the continent before Clovis,” Lorena Becerra-Valdivia, an archaeological scientist with the Universities of Oxford and New South Wales and co-author of the new studies, tells Mental Floss. “Within academia, an earlier arrival of 16,000-15,000 years ago was generally accepted.”

Her new analysis pushes back that date by several millennia. The study, “The Timing and Effect of the Earliest Human Arrivals in North America,” published in the journal Nature, looks at radiocarbon and luminescence data from Beringia, a region that historically linked Russia and Alaska, and North America. A statistical model built with this data indicates that a significant human population was living on the continent long before the Clovis era. According to the study, these humans were likely present before, during, and after the Last Glacial Maximum—the period when ice sheets covered much of North America 26,000 to 19,000 years ago.

Stone tool found below the Last Glacial Maximum layer.Ciprian Ardelean

These findings also contradict the land bridge theory. Rather than making a straightforward journey from Asia to North America and populating the southern half of the continent as the Clovis people were thought to have done, the first humans may have entered the Americas by traveling down the Pacific Coast. “These are paradigm-shifting results that shape our understanding of the initial dispersal of modern humans into Americas,” Becerra-Valdivia says. “They suggest exciting and interesting possibilities for what likely was a complex and dynamic process.”

The second, related study in Nature, ”Evidence of Human Occupation in Mexico Around the Last Glacial Maximum,” supports this new narrative. In it, researchers from institutes in Mexico, the UK, and other countries share artifacts and environmental DNA uncovered from Chiquihuite Cave—a high-altitude cave in Zacatecas, central Mexico. The tools, plant remains, and environmental DNA collected there paint of picture of human life dating back 13,000 to 30,000 years ago. The evidence shows that the site was more than just a stopping point, and the people living there had adapted to the high altitudes and harsh mountain landscape.

The two studies not only offer insight on when the first North Americans arrived on the continent, but who they were and how they lived. The Americas would have looked a lot different to humans during the Last Glacial Maximum than they did to the Clovis people millennia later. The fact that the first North Americans left behind far fewer artifacts than the Clovis people shows that their populations stayed relatively small. “Humans at Chiquihuite Cave would have faced the harshness of the Last Glacial Maximum, the peak of the last Ice Age, which would have kept their population at a low density,” Becerra-Valdivia says. “Clovis peoples, in contrast, thrived well after the last Ice Age, expanding widely through the continent during a period of globally warmer temperatures. Their life ways and subsistence patterns, therefore, would have been very different.”