Cavemen stayed home, while cavewomen roamed: study

Ancient hominid males stayed close to home while females roamed much more widely, according to a study that has prompted some anthropologists to suggest early cavemen had "foreign brides."

They say teeth from human ancestors have provided an unexpected glimpse of the social dynamic between the sexes that played out on the African savannah two million years ago.

The males appear to have stayed very close to their birthplace their entire lives while females moved around, leaving home when they reached sexual maturity.

"It’s quite surprising," said Michael Richards, at the University of British Columbia, co-author of the study to be published Thursday in the journal Nature.

The international team from Europe, Britain, the United States and Canada pointed high-powered lasers at 19 ancient teeth, which are some of the most precious fossils on the planet. The 2.4 to 1.7 million-year-old teeth belonged to two types of early hominids – eight Australopithecus africanus individuals and 11 Paranthropus robustus individuals.

The sample size is "huge" considering how few hominid fossils have been uncovered, said Richards, who splits his time between the University of British Columbia and Germany’s Max Planck Institute for Evolutionary Anthropology. "They’re are extremely rare," he told Postmedia News.

The team used a new "laser ablation" technique to analyze the teeth, which are stored in South Africa. The laser left a small mark on the ancient teeth, but Richards said "you can barely see it."

It enabled the researchers to assess the strontium content of the teeth, which can reveal where an individual grew up. This is because different types or isotopes of strontium are found in the rocks and soils from different geological areas. This leaves a distinct strontium signature in plants and animals, which incorporate the strontium in their teeth.

The scientists had set out to study how human ancestors had roamed and used the landscape. But they say the results revealed a striking and "totally unexpected" difference between the sexes.

Ninety per cent of the males "were born, raised and died in the vicinity" of the South African caves were the fossils were found, says co-author Darryl de Ruiter, of Texas A&M University. And more than 50 per cent of the smaller, presumably female teeth were from individuals who were "born and raised elsewhere."

The researchers say the males stuck to grasslands and woodlands on a long narrow band of dolomite-rick bedrock that covers about 30 square kilometres. The females were not local and appear to have moved into the region after they matured sexually.

U.S. anthropologists on the team are depicting the males as "stay-at-home-kind-of-guys when compared to the gadabout gals." Their British colleagues at Oxford University said the findings "suggests early cavemen had ‘foreign brides.’"

Richards cautioned it is not clear what was behind the social dynamic.

It is not known if early hominids were monogamous, he said, or if they raised their own young or communally.

The scientists said the males may have stayed in the same area because they preferred the food. Another possibility is that males worked together to defend their territory, like chimpanzees do.

"It could be that among these early hominids, female dispersal has some connection to close co-operation between males," Sandi Copeland of the University of Colorado Boulder told a media teleconference.

The findings do hint at a social structure two million years ago that is seen in some human cultures today, she said, noting how females continue to move to be with males in some hunter-gatherer societies.

Female dispersal is also seen with chimpanzees, she said. But other primates, such as gorillas, have harems dominated by one male with young males leaving the family group