The researchers noted first that the trees were very similar through the broadly encompassing classification of orders. In defining how the orders are related, however, the trees diverge considerably, suggesting that future researchers should focus their efforts at this very high level. "Our study narrows the scope of the problem," said Miyamoto, a member of UF's Genetics Institute.
The study further suggests that the molecular method may be better for resolving the relationships of orders, but not in every case.
To the contrary, the researchers found, where the trees disagree in the placement of the orders, the morphological method suggested the accepted solution about 20 percent of the time. Morphological evolutionists, for example, long argued that the orders for rodents and rabbits were closely related, a view only recently adopted by molecular evolutionists.
"There is a molecular bias against morphology, and I think this puts in better perspective what the values or merits of both can be," Miyamoto said.
The repercussions of the paper will go beyond evolutionists circles, researchers said.
By clarifying the evolutionary histories of other mammals, the placental mammal history will help scientists interpret the vast bulk of data generated in the human genome project. It would shed light, for example, on where people might have obtained certain genes and what role they played in their source animal ancestors.
"The tree is, in a sense, family history," Miyamoto said. "Doctors ask about family history to better understand your health. Biologists do the same to better understand genes and physical traits of humans, not to mention domestic animals and endangered species."
The paper also may prove useful in the emerging field of genomic "prospecting." In this field, scientists hunt for genetic clues to how living animals survived past
Contact: Michael Miyamoto
University of Florida