13 discoveries in the last year have fundamentally altered our understanding of human history

Anthropologists already knew that modern humans mated with Neanderthals and Denisovans — two cousins of Homo sapiens — 40,000 to 60,000 years ago.

But a February study showed that the ancestors of those Neanderthals and Denisovans once interbred with a mysterious population of ancient humans in Eurasia 700,000 years ago.

"This continues the story that we've been seeing in studies throughout the past decade: There's lots more interbreeding between lots of human populations than we were aware of ever before," Alan Rogers, an anthropologist at the University of Utah and the lead author of the study, previously told Business Insider. "This discovery has pushed the time depth of those interbreedings much further back."

Certain Neanderthal genes, researchers found, code for proteins that convey a heightened sense of pain to the spinal cord and brain. A July study showed that a sample of people from the UK who had inherited those Neanderthal genes experienced more pain than study participants who didn't have them.

Neanderthal hands were bigger than ours, and their thumbs stuck out at a wider angle from their palms than ours do.

According to a November study, this meant that precision grips like the ones we use when writing would have been challenging for Neanderthals.

But these ancestors had powerful squeeze grips — the kind one might need to swing a hammer.

But in February, researchers returned to a cave in Tibet where anthropologists had previously discovered a mysterious 160,000-year-old jawbone. They hypothesized last year that the bone belonged to a Denisovan, but had no genetic proof.

This time, however, they were able to collect ancient DNA from sediment in the cave. That led them to determine that the jawbone indeed came from a Denisovan who once thrived in the cave's harsh high-altitude environment.

Kira Westaway, an anthropologist from Macquarie University in Australia, told Business Insider that the discovery put "a lot more meat on the bones of the Denisovan story — the nature and length of their occupation, their ability to adapt to high-altitude locations, and their behavior and survival capabilities in the hostile environments of the Tibetan plateau."

Archaeologists determined that stone tools and artifacts discovered in a remote cave in Zacatecas, Mexico, were about 32,000 years old. They described the finding in a July study.

The new evidence upended the idea that the first people arrived in North America after continent-hopping from modern-day Siberia via the Bering land bridge between 18,000 and 13,000 years ago.

During the last Ice Age 32,000 years ago, that land bridge was impassable. So the research suggests the first Americans arrived by sea. According to the study authors, these migrants were likely anatomically modern humans.

Scientists discovered a 9,000-year-old burial site containing weapons and animal-skinning tools high in the Andes mountains of Peru. They assumed the human bones there came from a skilled male hunter.

But a closer look revealed that this hunter was female. Further analysis of 27 other burial sites across North and South America, which also contained hunting tools and date back to the same time period, revealed that 40% of the hunters were female.

"Female participation in early big-game hunting was likely nontrivial," the study authors concluded.

The finding "overturns the long-held 'man-the-hunter' hypothesis," Randy Haas, lead author of the study and an anthropologist at the University of California, Davis, said in a press release. This outdated archaeological theory suggested men were the primary hunters, while women gathered.

The drawings, which cover more than 2.5 miles of rock in Colombia, depict scenes of humans hunting mastodons. They also contain images of other extinct animals like giant sloths, ancient llamas, and Ice Age horses.

Archaeologists announced the drawings' discovery in late November.

A red pinwheel-shaped drawing found on the ceiling of a California cave may have been part of a hallucinogenic ritual nearly 500 years ago.

In addition to the drawing, researchers found chewed wads of datura stuffed into cracks in the ceiling of the cave. Their analysis also showed that people occupied the cave from about 1530 to 1890 and likely chewed the datura during that period.

According to a November study, the drawing could be evidence that paintings in caves have served as visual aids for drug-induced hallucinations.

More than 160 mummies have been found so far. They'd been buried for 2,500 years — until the first cache of 13 was found at the bottom of a 36-foot-deep shaft in September. Researchers have also found various artifacts in the tombs they've excavated, as well as a trove of animal mummies.

Further discoveries from the site are expected in the coming months.

Stonehenge, which is estimated to be about 5,000 years old, is made up of two distinct types of stone slabs set in half circles.

Researchers traced one type, the smaller bluestones, to a site in Wales 150 miles away. Research from July suggests the 30-foot (9-meter) sandstone boulders, called sarsens, that constitute the rest of the monument came from a nearby woodland area.

Still, Stonehenge's builders had to drag the 50,000-pound (22,700-kilogram) sarsens about 15 miles —"which is insane really if you think about it," archaeologist David Nash, the lead author of the study, previously told Business Insider.

According to a July study, the artifacts were underwater because sea levels rose and submerged 30% of Australia's coast line at the end of the last Ice Age 12,000 years ago.

The researchers found stone tools for cutting and chopping, as well as stones for grinding seeds. The tools were at least 7,000 years old, and they're conclusive evidence that Aboriginal people flocked to the coast for food and resources.

"People gravitate to coastlines," Jonathan Benjamin, an archaeologist at Flinders University and lead author of the study, previously told Business Insider. "But if you want to know what was happening on the coasts, you now have to go underwater."