When Charles Darwin proposed a theory of evolution by natural selection, the world of DNA and proteins was a complete mystery. But now, armed with powerful molecular techniques, UMBI scientist Jerry Regier is among those who have returned to the path blazed by Darwin in order to reconstruct the entire tree of life.

Instead of relying on the outward appearance or anatomy of whole organisms, a newer approach is based on tracing small changes in DNA. This method of estimating relationships between organisms is more precise than relying on visible differences alone. DNA is the common genetic material shared by all microbes, multicellular plants and animals ---- including those alive today, as well as those that have gone extinct millions of years ago.

Dr. Regier's laboratory focuses on estimating relationships within animal groups that encompass two major branches of the tree: One branch represents all arthropods ---- a mega-phylum of over one million species that includes insects, spiders, crabs, lobsters and barnacles. The other branch represents Lepidoptera ---- an insect order of approximately 150,000 species that includes butterflies and moths.

The fossil record indicates that arthropods evolved from their ancestors over 500 million years ago, sometime around the time of the Cambrian Explosion, when most of the other modern animal phyla also made their first appearance. The rapid appearance of the animal phyla, coupled with their long period of subsequent evolution, makes the reconstruction of their evolutionary history extremely challenging. Lepidoptera, by contrast, evolved from their insect ancestor perhaps "only" 200 million years ago, and much of their evolutionary diversification is coupled with that of flowering plants, on which many Lepidoptera -- but not the most ancient ones -- feed.

During the evolution of animals, species have branched off, or become reproductively isolated, from other species. Diverse forms of life can be represented as a single, continuously growing tree, in which the trunk and the thickest branches nearer the base represent the older lineages --like the arthropods-- and in which the thinner, outer branches nearer the top represent more recent lineages -- like the Lepidoptera. Extending this metaphor of the tree, each currently-living species can then be represented by a single leaf that is attached to one of the thinnest branches, which, together with all other leaves attached to that same branch, represents a "genus." Extinct groups of species can be represented by dead branches and their missing leaves. This tree metaphor may not apply as well to bacterial evolution, where a species concept may be less useful and where something between a tree and a network metaphor may better capture pictorially the complexity of the evolutionary processes, including the not-uncommon exchange of pieces of DNA across species.

At the level of DNA, species differences are represented by differences in the DNA sequences among species. This provides a more objective way of estimating relationships than visual groupings based on anatomical shape and form. When coupled with genome analysis, this new method of reconstructing the tree of life is called phylogenomics. In order for phylogenomics to be a reliable method of evolutionary investigation, each of the assumptions and mathematical models concerning the interpretation of differences in DNA must be rigorously tested and evaluated.

Interested readers can find a further discussion of the Tree of Life at the Tree of Life Web Project, a collaborative effort of biologists from around the world. On more than 5,000 World Wide Web pages, the project provides information about the diversity of organisms on Earth, their evolutionary history (phylogeny), and characteristics. To learn more about Dr. Regier's lepidopteran phylogenomics project -- and more about Lepidoptera -- go to http://www.leptree.net .