The emergence of complex tools may have coincided with the development of grammatical language, a new study in this week¿s Science proposes. Both skills have one thing in common: the need for complex problem solving and planning. As such, they may have influenced the evolution of the frontal lobe of the human brain, argues University of Illinois professor Stanley H. Ambrose, the paper¿s author.

The first-known stone tools were made about 2.5 million years ago, supposedly by Homo habilis. They were initially created through reductive technologies: a person continuously flaked away pieces of a rock until it turned into, say, a hand ax. Such techniques only require fairly crude and repetitive movements whose sequence is more or less irrelevant. The same goes for primate vocalization, which consists mostly of repetitive sounds.

Composite tools such as stone-tipped spears, however, require different talents, including fine motor skills and more forethought, to fit the different components of a tool together. So too, fine motor skills were needed to vocalize more complex sounds. (Just think of how you struggle to pronounce some sounds in a foreign language.) At the same time, sequence became relevant as language evolved from mere grunts to grammatically complex sentences.

Ambrose believes that all these developments were interconnected and led to a sudden burst in human development. "With the appearance of composite tools, near-modern brain size, anatomy and perhaps of grammatical language 300,000 years ago, the pace quickened exponentially," he says. "We became long-range planners and grammatical speakers. Composite tools made us what we are today."