|EMBARGOED FOR RELEASE 2 P.M. PST APRIL 26, 1999
Gagneux, lead author (619) 534-1346; Christopher Wills, second author (619) 534-5474;
David Woodruff, senior author (619) 534-2375; University Communications, (619) 534-3120
UCSD BIOLOGISTS COMPILE GENETIC HISTORY OF APES AND HUMANS; FAMILY
TREE SHOWS THAT HUMANS HAD BRUSH WITH EXTINCTION
A new report by evolutionary biologists at the
University of California, San Diego shows that the history of humans is quite different
from that of chimpanzees, bonobos and gorillas. The genetics study also supports the
controversial idea that humans have had at least one dramatic population reduction during
the last million years. The geographic patterns of genetic variation discovered also hold
clues to the origin of certain animal-born diseases, including HIV-1.
The international team of researchers, led by geneticists at UCSD, have completed an
unprecedented survey of genetic variation in humans and the African great apes
(chimpanzees, bonobos and gorillas) revealing for the first time the full extent of the
striking differences in patterns of variation between the species. The new family tree
shows that the great ape species are far more variable than the human species. One social
group of 55 chimpanzees in West Africa, for example, has much more variation than the
entire human species.
The distinct levels of genetic variation reflect differences in the age and history of
each species. It is now clear that human genetic history is dramatically different from
the histories of our closest relatives.
The study, published in the April 27 issue of the Proceedings of the National
Academy of Sciences, shows that our own population has undergone one or several
dramatic reductions in numbers sometime during the last million years.
"There was a period in our ancient history during which we came close to
extinction," said UCSD Biologist Christopher Wills, second author on the paper.
"Despite their much smaller numbers and restricted ranges, the African apes retain
much more genetic variation than humans," said lead author Pascal Gagneux, who
conducted the research as a doctoral student in the laboratory of David Woodruff, the
papers senior author. "The family tree also shows that the human branch has
been pruned. Our ancestors lost much of their original variability."
The reasons for this loss in variation are unknown, but they likely involved a
significant reduction in numbers due to one or a combination of disease, environmental
disaster or conflict.
The conclusions were based on a comparative study of 1,158 unique mitochondrial
control-region DNA sequences found to date in these four species of apes. As mitochondrial
DNA is inherited maternally, it permits researchers to reconstruct the history of the
females of a species. The results support the "mitochondrial Eve" hypothesis in
the history of human species.
The new data also shed light on the origin of HIV-1. Several researchers have concluded
that HIV-1 originated in central African chimpanzees after three were discovered with
chimpanzee Immunodeficiency Virus (SIVcpz).
Gagneux notes that the understanding of the evolution of chimpanzee viruses, and the
reason why some can infect humans and cause serious disease, will depend on a solid
understanding of the natural history of chimpanzee populations and their genetic
The new study is the first with large numbers of all four ape species of known
geographic origin. The genetic material from wild apes was obtained non-invasively from
DNA amplified from shed hair and fecal samples.
The results confirm that chimpanzees and bonobos are our closest living relatives. The
data suggest that they, and gorillas, are now threatened with extinction and their
survival depends on human help. The new family tree identifies genetically different
clusters of apes, each with its own irreplaceable genetic attributes and evolutionary
history. These genetic findings have important implications for both the conservation of
the remaining wild apes and the reproductive management of those in captivity.
"Conservation of the remaining great apes is critical," said Woodruff,
"as they still have so much to teach us about ourselves."
Pascal Gagneux, the leader of the scientific team and an authority on chimpanzee
evolution, currently is a post-doctoral fellow in Ajit Varkis laboratory at the UCSD
Cancer Center. Second author Christopher Wills, a leading evolutionary biologist and
author of the 1998 book Children of Prometheus (Perseus Books) on human evolution,
developed a powerful computer program to analyze the pattern of variation at the
half-million genetic sites studied. Senior author David Woodruff, an evolutionary
biologist and conservation geneticist, developed non-invasive methods of genotyping wild
chimpanzees. He published the first studies of their natural genetic variability.
Other co-authors, from Germany, Switzerland and the United States, contributed DNA
samples from across Africa.
The study was supported by the Swiss and US National Science Foundations and the
National Institutes of Health.
Note: Copies of the paper may be obtained by calling the National Academy of Sciences
Office of News and Public Information at (202) 334-2138.