The differences apparently date far back in evolutionary history to the time before humans and monkeys separated from their common ancestor some 25 million years ago, according to Gerianne Alexander, a psychologist at Texas A&M University in College Station, who led the experiment.
"Human evolution has created two different types of brains designed for equally intelligent behavior," Richard Haier, a neuroscientist at the University of California-Irvine, wrote in the journal NeuroImage.
Variety of toys used
In the monkey experiment, researchers put a variety of toys in front of 44 male and 44 female vervets, a breed of small African monkeys, and measured the amount of time they spent with each object.
Like little boys, some male monkeys moved a toy car along the ground. Like little girls, female monkeys closely inspected a doll's bottom. Males also played with balls while females fancied cooking pots. Both were equally interested in neutral objects such as a picture book and a stuffed dog.
People used to think that boys and girls played differently because of the way they were brought up. Now scientists such as Alexander say a creature's genetic inheritance also plays an important role.
"Vervet monkeys, like human beings, show sex differences in toy preferences," Alexander wrote in the journal Evolution and Human Behavior. "Sex-related object preference appeared early in human evolution," she said.
Alexander speculated that females of both species prefer dolls because evolution programmed them to care for infants. Males may have evolved toy preferences that involve throwing and moving, skills useful for hunting and finding a mate.
Upd: probably this was because the cooking pots were red, and the authors of the paper decided to spin their conclusions somewhat.