Genes Seem to Link Unlikely Relatives
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.
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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.
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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.