DURHAM, N.C. -- Classifying kangaroos and platypuses together on the evolutionary family tree is as absurd as adding your neighbors to your own family ancestral line simply because they share your love of the opera, according to scientists at Duke University.
But the current molecular method of using mitochondrial DNA to classify how mammals evolved is so flawed that it might have erroneously linked very different mammals, the scientists said. The mitochondrial DNA method of analyzing mammals has turned on its head the common-sense approach of linking mammals by similar anatomical traits or "morphology," they said.
Using a more comprehensive method to analyze the genetic material of 15 types of mammals, Duke researchers have shown that the mitochondrial DNA method that links disparate animals (hippo and whale, kangaroo and platypus) is statistically unreliable when it comes to evolutionary genetics, said Randy Jirtle, professor of radiation oncology at Duke University Medical Center. Their own research using nuclear genes (genes from the nucleus or core of cells) has shown a nearly 100 percent statistical likelihood that the Duke results are correct.
Mitochondria are the cell's power plants and possess their own genes that are inherited through the maternal line. Scientists use this method because mitochondrial DNA is more accessible, easier to sequence, and all multi-cellular animals have mitochondria, whereas all animals do not share the same nuclear genes.
Results of the study are published in the July 1, 2001 issue of the journal Mammalian Genome.
Such conclusive results led the researchers to strongly support the Theria hypothesis of classifying the three major groups of mammals. The Theria hypothesis holds that eutherians (humans, rats, pigs, whales, etc.) and marsupials (kangaroos, wallabies, koalas, etc.) have evolved from a common ancestor, and monotremes (platypus, echidna) have
Contact: Richard Puff
Duke University Medical Center