By state, school district, and the caprice of individual instructors, teaching evolution varies greatly across the United States.

In Kentucky, teachers preach the theory of evolution as well as its criticisms, including creationism or "intelligent design," which proposes that certain aspects of the universe and its living inhabitants are best explained by an intelligent progenitor, rather than undirected processes such as natural selection.

Kansas and Ohio, too, teach criticisms of evolution while Colorado and New York permit county school districts, schools, and teachers to decide how to portray the subject to students. And with nearly five million students in the school system, Texas exercises influence over the textbook curriculum of the rest of the country — its religious-conservative politics greatly informing the didacticism of subjects such as evolution.

But aside from the split between evolutionists and creationists in America, a new study published in the July issue of BioScience shows a new divide in approach to the teaching of evolution. Wheareas students in most classrooms learn a fragmented version of evolution, studying isolated examples of how the evolutionary process works, some instructors have begun to teach a more integrated curriculum explaining how evolution works on a molecular level to effects seen on a population basis.

Thus, researchers at Michigan State University have developed a curriculum of evolutionary case studies which they tested on college students in a cellular and molecular biology course at the university's Lyman Briggs College.

In the course, students learned about the evolution of the sweet taste and wrinkled skin of domestic garden peas, and about the evolution of light or dark colored beach mice living on light or dark sand. After the lessons, students improved noticeably in their ability to explain the theory of evolution as a whole, according to lead investigator Peter J.T. White.

On the elementary school level, at least one school district already incorporates a more holistic approach to the teaching of evolution. Karen Pickett Dieter, a biology teacher at Woodland Middle School in North Port, Fla., says she teaches her students about the structural, behavioral, and functional facets of evolution.

"We start with the fossil record then I get into talking about Lamark and Darwin," Dieter said. "We discuss gene mutations and how they cause variations — natural, artificial, and sexual selection. We discuss real world examples of evolution that we can see: for example, antibiotic and insecticide resistance."

Although researchers say "suprisingly few" teachers incorporate comprehensive evolutionary case studies, the number is growing.