A challenge to Dollo’s law of irreversibility

Dollo's law, named for the 19th-century palaeontologist Louis Dollo, states that evolution always moves forward – that an organism cannot redevelop an organ or attribute discarded by its ancestors. But new research on humble dust mites, the tiny arachnids that live in cushions and carpets everywhere, is challenging the law. Using DNA data to construct an elaborate family tree, two University of Michigan biologists have shown that dust mites – which are not parasites but free-living organisms – evolved from parasites that in turn evolved from other free-living organisms. That would seem to contradict Dollo's law, since the mites should be unable to readopt the free-living characteristics discarded by their ancestors. "The results show pretty conclusively that dust mites are derived from parasitic ancestors," said Barry O'Connor, an evolutionary biologist and one of the authors of the study, in the journal Systematic Biology. How does a mite evolve in reverse? The family tree – known as a phylogeny – showed that the closest living relatives to the dust mites are all able to tolerate low humidity and to digest tough materials like skin and keratin. The researchers think this helped the mites break free from birds and mammals to live off material found in nests and homes. The discovery that dust mites evolved from parasites could also help provide relief for people with allergies. Knowing the genetic background could give insight into the allergenic properties of the proteins in the mites that set off an immune response in humans. time of oman