Washington, Nov 13 (IANS): Researchers have found evidence that men evolved better navigation ability than women to engage in increased sexual activities because men with better spatial skills - the ability to mentally manipulate objects - can roam farther and beget children with multiple mates.

By testing and interviewing dozens of members of the Twe and Tjimba tribes in north-west Namibia, anthropologists showed that men who did better on a spatial task not only travelled farther than other men but also had children with more women.

"Navigation ability facilitates traveling longer distances and exploring new environments. The farther you travel, the more likely you are to encounter new mating opportunities," said Layne Vashro, the study's first author and Post-Doctoral Researcher in Anthropology from the University of Utah in the US.

"The Twe and Tjimba were good subjects for the study because they travel over distances of 120 miles during a year, navigating on foot in a wide-open natural environment like many of our ancestors," Vashro added.

The tribes have a comparatively open sexual culture.

"They have a lot of affairs with people they are not married to and this is accepted in their culture. Many men have children by women other than their wives," the authors said.

The findings showed that men travelled father than women and to more places than women.

Men reported visiting 3.4 unique locations across 30 miles per location on an average in a year, while women reported visiting only two locations across 20 miles, Vashro said.

"It looks like men who travel more also have children from more women - what you would expect if mating was the payoff for travel," he added.

The study was published in the journal Evolution and Human Behavior.