What makes a human different from a chimpanzee? Not much, but the little genetic differences clearly count for a lot, said scientists who have mapped the complete chimp genome and compared it to the human gene map.
They said their findings, published in the journal Nature on Wednesday, would shed light on why people get Alzheimer’s disease, certain cancers and even AIDS, which chimpanzees do not.
The researchers said the findings were yet more proof that evolution is real and works through natural selection, just as Charles Darwin predicted a century ago.
“As our closest relatives, they (chimpanzees) tell us special things about what it means to be a primate and, ultimately, what it means to be a human at the DNA level,” Dr. Francis Collins, head of the National Human Genome Research Institute, which funded the studies, told a news conference.
Dr. Robert Waterston of the University of Washington in Seattle and colleagues sequenced the DNA of a chimpanzee named Clint, who is now dead.
They compared it to the human genome sequence and did a letter-by-letter comparison of the DNA base pairs — the A, C, T and G nucleotides that make up both the human and chimp genetic codes.
Out of 3 billion base pairs that make up both the human and the chimpanzee genomes, only 40 million differ between human and chimp, they found.
Most are changes in a single letter — for instance a human has an A where a chimp has a T.
In addition, humans have some extra DNA that chimps do not have and vice-versa.
All these differences add up to 4 percent of the total genomes — meaning humans and chimps are 96 percent genetically identical.