WASHINGTON (Reuters) – 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
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
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
BASIS FOR HUMANITY
“If you see a difference between a chimp and a human, it is
clearly the result of a single evolutionary event,” Waterston
“Within those 40 million events, we clearly have the basis
for what makes us human.”
Humans and chimps evolved separately from a common ancestor
that lived about 6 million years ago.
Three different types of genes seem to be evolving rapidly
in both humans and chimpanzees, said Washington University’s
Dr. LaDeana Hillier — those involved in reproduction, smelling
“The vast majority of these 40 million changes are probably
not relevant to what makes us human because they are in junk
DNA,” said Tarjei Mikkelsen, a graduate student at the Broad
Institute, a joint venture of the Massachusetts Institute of
Technology and Harvard University who led one study.
He said only about 5 percent affect proteins that are
likely to have a large effect on biology.
Among them, a parasite related to sleeping sickness that
infects chimps but not humans, and one gene for sialic acid,
which is found on the surfaces of cells and is used by some
viruses to infect them.
There is also an enzyme called caspase 12, which is mutated
in humans and appears to make our species susceptible to the
brain-wasting Alzheimer’s disease, Mikkelsen said.
The researchers said their findings clearly contradicted an
increasingly vocal movement in the United States that disputed
the science of evolution and instead called for teaching
creationism or the idea of intelligent design to school
“To me, looking at this — we are looking at evolution in
action,” Waterston said.
“I couldn’t imagine Darwin hoping for a stronger
confirmation of his ideas when we compare the human and the
But, added Collins, the study did not address philosophical
or religious questions. “It may very well not tell us about
other aspects of humanity, such as how do we tell right and
wrong,” Collins said.