May 28 (Bloomberg) -- Human DNA inserted into mice caused their offspring to squeak at a different pitch, suggesting that the gene involved may be linked to people’s ability to speak.

The gene variant exists only in humans, meaning it developed after people separated evolutionarily from chimps. By inserting the gene into mice and measuring how it changed them, scientists at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, aimed to gain insight into the genetic forces that produce behavior unique to humans.

Researchers led by Wolfgang Enard engineered mice to carry a human version of the FOXP2 gene, which may play a role in speech and in language disorders. Pups bred from the genetically modified mice whistled at lower pitch than did their ordinary cousins, the scientists said today in the journal Cell.

The genetic changes in the mice may have “contributed to an increased fine-tuning of motor control necessary for articulation,” the researchers wrote, which is “the unique human capacity to learn and coordinate the muscle movements in lungs, larynx, tongue and lips that are necessary for speech.”

The FOXP2 gene affects the development of many organs, including the brain, lungs and esophagus, the researchers said.

The study was the first to explore the effect of modifying genes in an animal and the relevance to human evolution, according to the authors. The researchers said they used mice because it would be impossible or unethical to genetically manipulate chimps or humans, and mice are the only mammal that can easily have genes modified and the effects measured.

In addition to the difference in squeaks, Enard and his colleagues found that the mice endowed with the human FOXP2 genes had changes in their brains. The alterations included lower levels of the chemical dopamine and longer dendrites, the branch-like projections of neurons. The mice also did less exploring of a board set up for them to wander in.

To contact the reporter on this story: Rob Waters in San Francisco at rwaters5@bloomberg.net.

Last Updated: May 28, 2009 18:26 EDT