"Firstly, it means that a given hemisphere can become increasingly specialized at processing certain types of information," he said. "You can ask a handyman to fix your tap, but you are better off asking a plumber to do it."

confirms the hypothesis that lateralization enhances cognitive performance."

Yet why do females, be they bowerbird or human, favour more intelligent males? Although the two species last shared a common ancestor tens of millions of years ago and humans tend to practice monogamy, while bowerbird males mate with as many females as possible, there may be a common explanation. Females could use intelligence as an indicator of the genetic quality of a potential mate and the genes he will pass onto her kids. "A male that has a well functioning brain is probably going to be good at surviving," Keagy says. "It's almost like a way of interpreting all this information about the genetic quality of a male." In two recent studies Geoffrey Miller of the University of New Mexico in Albuquerque and his wife Rosalind Arden of King's College in London have found provisional evidence for the same effect in humans.