The concept of the “man cave” has been entrenched in the human lineage for far longer than thought, according to new research that analyzed teeth from early humans to determine their geographic movement.
Scientists from the University of Colorado at Boulder found that males of two hominid species that roamed the South African savanna more than a million years ago stayed close to home—which often included caves—while females tended to move away.
The study, published in the June 2 issue of the journal Nature, suggests that fossils can reveal clues to early humans’ social and gender-related behavior, said Jeffrey Laitman, director of the Center for Anatomy and Functional Morphology at the Mount Sinai School of Medicine in New York City.
“This is strong and beautiful science,” Laitman said. “It at least is giving us a glimpse that some of the behaviors we see today have roots going into the past. It may well be in our lineage that [males] liked their man caves.”
Study author Sandi Copeland and her team studied teeth from a group of extinct Australopithecus africanus and Paranthropus robustus individuals from two adjacent cave systems in South Africa, finding that more than half of the female teeth were from outside the local area. But only about 10 percent of the male hominid teeth were from elsewhere, the study said, suggesting they likely grew up and died in the same area.
Using a high-tech analysis known as laser ablation, the researchers zapped the hominid teeth with lasers to measure isotope ratios of strontium found in tooth enamel, which helped identify specific areas of landscape use. Strontium is a naturally occurring element found in rocks and soils that is absorbed by plants and animals.
Copeland, an adjunct assistant professor of anthropology at UC-Boulder, said she was surprised when results initially found no significant disparities in how the two early human species used the landscape. When males were compared to females, however, noticeable differences emerged.
“Our study is the first to directly test the dispersal pattern that might have [existed] in early hominids,” she said.
The strontium isotope ratios reflected their locations, and therefore what foods were available, Copeland said. The team tested 19 teeth dating from approximately 1.8 million to 2.2 million years ago, determining that male teeth were larger than those from females. They also compared them to teeth and jaw fossils from five early hominid sites in South Africa.
The “million-dollar question,” Copeland said, is why males from these groups stayed closer to home while females roamed. Among most other primates, including gorillas, this pattern is reversed.
Determining the reasons “is very hard,” Laitman said. “I think they’re going to have to extrapolate a bit, but at least we have the beginnings of the story. I don’t think this is by chance—I think their data is real, and they’re cracking open the behaviors of our ancestors.”
Copeland noted that future technology may make it possible to move beyond this knowledge to learn why this geographic movement pattern existed among early humans.
“I think there’s hope for doing something like that,” she said.