June 24, 1999 -- Earthworms are kin to lobsters and flatworms are cousins of roundworms. These kinds of relationships have been drawn over the years by zoologists who painstakingly constructed evolutionary trees using animal morphology, or comparisons of form and structure. Morphology was, until recently, the best information available for such classifications. But new molecular evidence -- gleaned directly from DNA, the master blueprint of life -- is pruning the old evolutionary tree.

"Basically, we're redrawing the tree," says Jennifer Grenier, a Howard Hughes Medical Institute (HHMI) associate at the University of Wisconsin-Madison.

Grenier and HHMI investigator Sean Carroll, also at Wisconsin, were part of an international research team that performed the latest tree trimming. Their work substantiates earlier genetic investigations suggesting that the vast majority of animals, from oysters to humans, belong to one of three primary evolutionary lines, rather than the multiple branches suggested by morphological studies. The researchers reported their findings in the June 24, 1999, issue of the journal Nature.

Grenier and Carroll had been exploring the genetic regulation of animal development when they realized that the genes they were studying could shed light on animal evolution. Members of the Hox gene family ensure that organs and other systems form properly and in the appropriate places in the developing animal. For example, a Hox gene called Ubx allows only one pair of wings to arise in a fruit fly instead of the two pairs found in a dragonfly. Mutations in Hox genes cause severe abnormalities.

Because Hox genes are ubiquitous and well conserved -- having changed very slowly throughout animal evolution -- they provide powerful clues about the evolutionary history of
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
24-Jun-1999