The genetic make-up of our closest living relative, the chimpanzee, has been sequenced and analysed by an international team of researchers.
The scientists say the information is a milestone in the quest to discover what sets us apart from other animals.
A comparison shows chimps and humans to be almost 99% identical in the most important areas of their "life codes".
The team tells Nature magazine that future research will tease out the significance of the few differences.
The study was undertaken by an international group called the Chimpanzee Sequencing and Analysis Consortium, which was made up of 67 scientists at 23 research institutions in the US, Germany, Italy, Israel and Spain.
Fundamental questions
The work provides a catalogue of the genetic differences that have arisen since humans and chimpanzees diverged from a common ancestor some six million years ago.
"As our closest living evolutionary relatives, chimpanzees are especially suited to teaching us about ourselves," said the study's senior author, Robert Waterston, chair of the Department of Genome Sciences of the University of Washington School of Medicine in Seattle.
"We still do not have in our hands the answer to a most fundamental question: What makes us human? But this genomic comparison dramatically narrows the search for the key biological differences between the two species."
The researchers hope that by elaborating those few points of separation, they will also increase pressure to save chimpanzees and other great apes in the wild.
The study shows that our genomes are startlingly similar. We differ by only 1.2% in terms of the genes that code for the proteins which build and maintain our bodies. This rises to about 4%, when non-coding or "junk" DNA is taken into account.
The long-term goal of the project is to pinpoint the genetic changes that led to human characteristics such as complex language, walking upright on two feet, a large brain and tool use.
Medical gain
Comparing our genome with other species provides a treasure trove of information for understanding human biology and evolution.
"As the sequences of other mammals and primates emerge in the next couple of years, we will be able to determine what DNA sequence changes are specific to the human lineage," said the study's lead author, Tarjei Mikkelsen, at the Broad Institute of the Massachusetts Institute of Technology and Harvard University.
CHIMP DNA - PAN TROGLODYTES
"The genetic changes that distinguish humans from chimps will likely be a very small fraction of this set."
There should be significant gains for medicine. Already, it can be seen that three key genes involved in inflammation - a root cause of many human diseases - appear to be absent from chimps.
This could explain some of the known differences between chimps and humans affecting immune and inflammatory responses.
Humans, on the other hand, seem to have lost a functioning caspase-12 gene, which may protect other animals against Alzheimer's disease.
The DNA for the study came from the blood of a male chimp called Clint, who was housed at the Yerkes National Primate Research Center in Atlanta.
The chimp died from heart failure last year but some of his cells have been preserved for future research.
The species studied is the common chimpanzee (Pan troglodytes). Its only sister species is the pygmy chimpanzee, or bonobo (Pan paniscus).
The chimp's is one of more than two dozen mammalian genomes that have or are currently being sequenced and analysed, including the mouse, the rat, the dog and the cow.
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