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SCIENCE NEWS

Week of January 6, 2001; Vol. 159, No. 1

Genes Seem to Link Unlikely Relatives
Sid Perkins

The Afrotheria grouping includes both 50-gram elephant shrews (top) and
5,000-kilogram elephants (bottom).

Similarities in DNA, the genetic material that's passed along from an animal
to its offspring, can be a strong indicator of kinship. After all, even if you
didn't get your father's nose, you got a hefty dose of his DNA.

Using that line of reasoning, an international team of scientists contends
that markers in the genes of three proteins suggest a single African
ancestor for animals as diverse as elephants and aardvarks. The
researchers, led by scientists at the University of Nijmegen in the
Netherlands, present their findings in the Jan. 2 Proceedings of the National
Academy of Sciences.

Almost a third of the major groupings, or orders, of mammals actually can
be lumped into a superorder called Afrotheria, says Wilfried W. de Jong, a
molecular biologist at the University of Nijmegen and a coauthor of the
report. Scientists had previously linked some of these animals, such as
elephants and hyraxes, because of similarities in bone structure or other
characteristics, de Jong notes. Although they sport similar genetic markers,
other newly proposed group members-such as aardvarks and golden
moles-have no obvious physical similarities to their supposed cousins.

"This is an odd collection of mammals, and it's tough to convince biologists
who depend on morphology that this is a valid grouping," admits S. Blair
Hedges. An evolutionary biologist at Pennsylvania State University in
University Park, he says in the same issue of the journal that the genetic
similarities can best be explained by a common ancestor.

Morphologists, who seek biological relationships among organisms,
typically look for common traits such as feathers or fur to discern kinship,
says Hedges. In this particular case, he notes, the researchers have applied
the morphologists' rules of classification to genetic instead of structural
markers.

"One hopes that molecules and morphology would tell the same story,"
says de Jong. But when the two differ, he contends, genetic markers are
simpler to interpret.

It's always possible that convergent evolution could cause a particular
physical feature to evolve, de Jong notes. However, he says, he can't
imagine a biological mechanism that could randomly cause matches in
markers on the genes for three different proteins in the Afrotherians.
According to the team's statistical analyses, the probability of such an event
is negligible.

Over the past 3 years, studies of genetic material by de Jong and his
colleagues have indicated that Afrotherians are descended from a species
that probably lived about 100 million years ago. This common ancestor
evolved in an Africa isolated after it split from South America but before
the continent drifted eastward to join Eurasia and was likely a small forest
dweller that ate insects, Hedges says.

Although there are no physical characteristics that distinguish the animals
linked by the genetic analysis, Hedges says, the combination of the
molecular evidence, the geographic distribution of the animals today, and
the geologic history of the African continent provides convincing support
for their kinship.

References & Sources

References:

Hedges, S.B. 2001. Afrotheria: Plate tectonics meets genomics. Proceedings
of the National Academy of Sciences 98(Jan 2):1.

van Dijk, M.A.M.,...W.W. de Jong, et al. 2001. Protein sequence signatures
support the African clade of mammals. Proceedings of the National Academy
of Sciences 98(Jan. 2):188.

Sources:

S. Blair Hedges
Department of Biology
Institute of Molecular Evolutionary Genetics and Astrobiology
Research Center
208 Mueller Laboratory
Pennsylvania State University
University Park, PA 16802

Wilfred W. de Jong
Department of Biochemistry
University of Nijmegen
P.O. Box 9101
6500 HB Nijmegen
Netherlands

>From Science News, Vol. 159, No. 1, Jan. 6, 2001, p. 4.

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