Yapping at the drop of a hat, a carefully coiffed toy poodle
hardly inspires the awe of a howling timber wolf.
Based on a study by an international team of biologists,
however, it may be time to show Fifi a little more respect. By
comparing genetic material from dogs with that of wolves, coyotes,
and jackals, the researchers have proved what zoologists have long
suspected: Domestic dogs descended from wolves.
What's more, the scientists say, their work suggests that
canines were in the process of becoming man's best friend between
60,000 and 135,000 years ago - as much as 121,000 years earlier
than the archaeological record suggests.
Up to now, the case for the wolf as the pooch's forerunner has
largely rested on physical and behavioral similarities, as well as
archaeological records, according to Robert Wayne, associate
professor of biology at the University of California at Los Angeles
and a member of the research team. He and his colleagues, however,
hunted at the molecular level for the biological equivalent of the
To do so, "we wanted to sample as many breeds as possible," Dr.
Wayne says. These ranged from greyhounds and Australian dingos to
more modern schnauzers, setters, and spaniels.
Overall, the team's study involved 162 wolves from 27 locations
worldwide and 140 dogs from 67 breeds. Five coyotes and a dozen
jackals were also included because all wild species of canines can
interbreed, and these species seemed the most likely alternative
candidates as forebears to the modern dog.
The evidence the team sought is locked up in mitochondria, tiny
organs inside cells responsible for supplying the energy the cell
needs. These tiny powerhouses, which lie outside the cell's
nucleus, are governed by their own self-contained DNA, the molecule
that holds the basic chemical building blocks of organic life.
Mitochondrial DNA has two things going for it as evolutionary
historian. It evolves faster than the DNA in the cell's nucleus,
where an organism's entire genetic blueprint resides.
These changes take place over thousands of years, instead of
millions of years for nuclear DNA, so researchers have more points
of comparison. And mitochondrial DNA is passed only from mother to
offspring, so it is less confusing to decipher than nuclear DNA,
which gets jumbled as it's shuffled between males and females and
is a larger molecule to untangle.
After taking DNA samples from their subjects and comparing
images of a common region in the mitochondrial DNA, "the only
evidence was for wolf ancestry, with two or three episodes of
interbreeding" between wolves and dogs after dogs began running
with humans or their ancestors, Wayne says. …