BLOOMINGTON, Ind., Nov. 15: A gene thought to influence perception and susceptibility to drug dependence is reportedly expressed more readily in human beings than in other primates.

And that difference, say Indiana University-Bloomington researchers and scientists at three other academic institutions, coincides with the evolution of our species.

The gene encodes prodynorphin, an opium-like protein implicated in the anticipation and experience of pain, social attachment and bonding, as well as learning and memory.

"Humans have the ability to turn on this gene more easily and more intensely than other primates," said computational biologist Matthew Hahn, who conducted most of the study's population genetics work. "Given its function, we believe regulation of this gene was likely important in the evolution of modern humans' mental capacity."

The scientists say their report supports a growing consensus among evolutionary anthropologists that hominid divergence from the other great apes was fueled not by the origin of new genes, but by the quickening (or slowing) of the expression of existing genes.

The research, conducted by Hahn and colleagues at Duke University, University College London and the Medical University of Vienna, appears in the December issue of Public Library of Science Biology.