In the search for evolution's inner workings, beetles would appear fruitful candidates for study.

Beetles are diverse, numerous, and widespread—an estimated 5 to 8 million species are found on six continents. Of all the insect species that are named, 40 percent are not bees or termites or mosquitoes, but beetles. Some beetles are pests, like the potato beetle, while others are helpful, like the ladybugs that eat garden aphids. One group of beetles that generally goes unnoticed despite its positive effects on human life and the ecosystem functioning are dung beetles, those industrious recyclers of animal waste. As it turns out, the lowly dung beetle is a showcase for the complex and unusual paths evolution sometimes takes in making something new.

Indiana University Bloomington biologist Armin Moczek is interested in all beetles, but focuses the majority of his scientific work on studying those with horns, a type of beetle that happens to be particularly common and impressive among dung beetles.

As nature programs tell us, beetles use their horns as jousting weapons in sometimes deadly combat over females. But a beetle's horns serve far less obvious functions, too, Moczek argues, and these hidden functions may represent the original reason why beetle horns evolved in the first place.

Moczek took a close look at species where only some individuals have big horns, such as large males, while females or small males appeared hornless. He brought these species into the laboratory and reared them for several generations, observing that all the individuals—males, females, large and small—grew horns at early developmental stages. But the majority of the beetles in the lab would reabsorb their horns, turning into hornless adults. The only ones to retain their horns were large males. Moczek looked at additional species and found that this here-and-gone developmental pattern of horns was common. So, why bother growing horns in the first place?

The answer became clear when Moczek found a way to prevent beetle larvae and pupae from having horns. It quickly became clear that larval and pupal horns were crucial devices for the correct molting of larval and pupal shells during metamorphosis. Without them, developing beetles remained stuck in their old shells, destined to die. "It turns out that simple pupal horns really are very widespread, including beetles that never have horns in the adult stage," Moczek says. His findings suggest that pupal horns came first, helping juvenile beetles with molting and metamorphosis, and only secondarily became the weapon of choice among adult beetles.

How young animals develop is interesting in its own right, but to evolutionary biologists, development is more than growth and differentiation. In the case of animals, plants, and some fungi, development is the thing evolution acts on. Evolution doesn't build on structures – such as red feathers or long necks -- so much as it builds on the developmental processes that create those structures. Development is a window into what it takes for an organism to build itself, and what it takes for evolution to modify this process.

Because of evolution's idiosyncrasies, development has the habit of illuminating strange biological history. A familiar example is the temporary formation of gill slits during a human embryo's development. Reabsorbed horns and vanishing human gill slits make development and evolution sometimes seem not only illogical but also wasteful.

"If you look at things from an engineering perspective, sometimes it seems nature comes up with the most optimal solution," Moczek says. "In other cases, evolution clearly takes circuitous routes to its ultimate destination. And sometimes it produces traits that are without question poorly designed. Evolution can only work with what it has, with what development will allow.”

If scientists never paid attention to development during the early stages of an individual's growth, key information about the evolution of modern organisms would go unnoticed. "Even today, evolutionary theory is very much a theory of adults," Moczek says. "But evolution doesn't morph one adult shape into another. Instead there's an entire lifetime of development that we can't afford to ignore."