New Analyses Bolster Central Tenets of Evolution Theory

When Lenski and his colleagues examined each strain's genes, they found that the strains had not acquired the same mutations. Instead, there was some variety in the happy accidents that had allowed each culture to survive. And when the 12 strains were then subjected to a different stress -- a new food source -- they did not fare equally well. In some, the changes from the first round of adaptation stood in the way of adaptation to the new conditions. The 12 strains had started to diverge, taking the first evolutionary steps that might eventually make them different species -- just as Darwin and Wallace predicted.

In fact, one of the more exciting developments in biology in the past 25 years has been how much DNA alone can teach about the evolutionary history of life on Earth.

For example, genome sequencing projects have shown that human beings, dogs, frogs and flies (and many, many other species) share a huge number of genes in common. These include not only genes for tissues they all share, such as muscle, which is not such a surprise, but also the genes that go into basic body-planning (specifying head and tail, front and back) and appendage-building (making things that stick out from the body, such as antennae, fins, legs and arms).

As scientists have identified the totality of DNA -- the genomes -- of many species, they have unearthed the molecular equivalent of the fossil record.

It is now clear from fossil and molecular evidence that certain patterns of growth in multicellular organisms appeared about 600 million years ago. Those patterns proved so useful that versions of the genes governing them are carried by nearly every species that has arisen since.

These several hundred "tool kit genes," in the words of University of Wisconsin biologist Sean B. Carroll, are molecular evidence of natural selection's ability to hold on to very useful functions that arise.

Research on how and when tool kit genes are turned on and off also has helped explain how evolutionary changes in DNA gave rise to Earth's vast diversity of species. Studies indicate that the determination of an organism's form during embryonic development is largely the result of a small number of genes that are turned on in varying combinations and order. Gene regulation is where the action is.

Consequently, mutations in regulatory portions of a DNA strand can have effects just as dramatic as those prompted by mutations in genes themselves. They can, for example, cancel the development of an appendage -- or add an appendage where one never existed. This discovery refuted assertions by Intelligent Design advocates that gene mutation and natural selection can, at most, explain the fine-tuning of species.

"The mechanisms that make the small differences between species are the same ones that make the big differences between kingdoms," said Carroll, author of a book, "Endless Forms Most Beautiful," that describes many of these new insights.

Although the central tenets of evolution have done nothing but grow stronger with every experimental challenge, the story is still evolving, Carroll and other scientists acknowledge. Some details are sure to be refined over time. The question to be answered in Harrisburg is whether Intelligent Design has anything scientific to add for now, or whether it belongs instead in philosophy class.