Men evolved better navigation ability than women because males with better spatial skills - the ability to mentally manipulate objects - can roam farther and have children with more mates, a new study suggests.
By testing and interviewing dozens of members of the Twe and Tjimba tribes in northwest Namibia, researchers showed that men who did better on a spatial task not only travelled farther than other men but also had children with more women.
These findings offer strong support for the relationship between sex differences in spatial ability and ranging behaviour, and identify male mating competition as a possible selective pressure shaping this pattern, researchers said.
"Navigation ability facilitates travelling longer distances and exploring new environments," said Layne Vashro, the study's first author and a postdoctoral researcher in anthropology at the University of Utah.
"And the farther you travel, the more likely you are to encounter new mating opportunities," said Vashro.
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.
The tribes "have a comparatively open sexual culture," Vashro said.
They have a lot of affairs with people they are not married to, and this is accepted in the culture. Many men have children by women other than their wives.
The findings show 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 average in a year, while women reported visiting only two locations across 20 miles, researchers said.
Men who did better on the mental rotation task reported travelling farther both during their lifetime and the past year, compared with men who did not do as well on the mental rotation task.
"It looks like men who travel more in the past year also have children from more women - what you would expect if mating was the payoff for travel," Vashro said.
The study was published in the journal Evolution and Human Behaviour.
