An international team of scientists has completed a rough draft of the DNA of our closest primate relative, the chimpanzee, and made a comprehensive comparison with the human genetic blueprint.  While there were no startling findings, the work may eventually answer the age-old scientific question:  What makes us human?

Humans and chimps evolved separately since splitting from a common ancestor about six million years ago.  The question has always been, what genetic differences led to our unique traits, such as the ability to walk upright and develop speech?

Hoping one day to answer that question, an international consortium of 67 researchers has completed a rough draft of the roughly three billion building blocks of chimpanzee DNA and compared it to a road map of the human genetic sequence.

In a series of papers to be published in the journals Nature and Science, the investigators report that 96 percent of humans and chimp DNA is identical.  But future research will focus on the remaining four percent of genes that are different, distinguishing us from our nearest primate relative, according to Robert Waterston head of the Department Genome Sciences at the University of Washington School of Medicine in Seattle.  Dr. Waterston directed the Chimpanzee Sequencing and Analysis Consortium project.

"What you are actually seeing are the individual events that have taken place in the course of evolution," he said.  "If you see a difference between chimp and human it's almost certainly because of a single evolutionary event."

For example, Dr. Waterston and his colleagues compared genes in chimps and humans that regulate the activity of other genes.  The investigators found the master genes had undergone rapid changes in humans, but not in the non-human primates.

In a paper published in Science, German researchers report finding that genes common to both chimpanzees and humans appear to have become more active in the brains of humans.  But the activity of shared genes in other organs, such as the heart, remained the same.

Professor Waterston says the human genetic roadmap and now the completed chimpanzee DNA blueprint offer investigators a catalogue of information.

"This ability to draw evolutionary comparisons really adds great richness to what would otherwise be a one-dimensional story.  And now, we can look at it through the lens of evolution and peak into evolution's lab notebook at see what really went on there," added Dr. Waterson.

In addition to providing answers to long-sought questions about evolution, researchers say they may some day be able to use the genetic differences between humans and chimps to understand how diseases arise and to develop new therapies.