It's one of the greatest challenges for robotics engineers: Building a machine that actually walks like one of us.
So far, most attempts have come off as, well, robotic.
Scientists in the field of biologically inspired design are looking at nature to help solve such stumpers. They argue that engineers can learn much from the world's most rigorous process: Evolution.
"If you think of organisms as products, all the bad ones have been recalled. Those that have survived evolved over millions of years," said Marc Weissburg, a biology professor and co-director of Georgia Tech's Center for Biologically Inspired Design.
People have always looked to nature for inspiration, capturing the sun to create fire and copying birds to achieve flight. But in the last 30 years, such observations have become the foundation of an increasingly popular scientific field.
Two research centers opened up within the last year, one at Georgia Tech in Atlanta and another at the University of California, Berkeley. And last month, dozens of researchers gathered in Atlanta to share their experiments in what observers said was a sign of the field's coming of age.
A range of projects were on display, including investigations into rat whiskers, fish jaws and worm brains.
"It really captures the imagination to show how much better organisms are at doing things," Weissburg said. "The natural world doesn't waste energy, accumulate a large amount of toxins or produce more materials than it uses."
Weissburg's pet project shines a blinding green laser into a pool of water to track how a blue crab still manages to swallow a piece of shrimp in 15 seconds even though it can't see.
Hang Lu, another professor, is looking to common worms to learn how to develop sensors that can one day distinguish smell. Eventually, she said, the technology could be used to track plumes of smoke from miles away and determine what is burning.
German scientist Rolf Muller, who teaches at China's Shandong University, says his investigation of bat ears could improve sonar technology. And Robert Full, a Berkeley researcher, is trying to learn the stability principles that keep six-legged insects, eight-legged crabs and four-legged dogs upright.
The field has enjoyed a few recent popular successes, including cleaning products and paints that capture how some plants prevent water from sticking to leafy surfaces — effectively repelling dirt and contaminants.
Skeptics say the relative dearth of discoveries and the staggering cost to develop them isn't worth the final product.
The field also is criticized by intelligent-design backers who say scientists are revering a system that's so complex that it had to be engineered by a higher power.
On his Web site, William Dembski, a leading activist for the intelligent-design movement, dismissed the Georgia Tech center.
"Here's how it works: we find some amazing system in the biological realm, determine how to reverse engineer it, and then design and build a parallel system to serve our needs," he wrote. "But of course, the original system evolved by blind trial-and-error tinkering ... To think that it was actually designed because we had to design its human counterpart is just plain stupid."
Scientists in the field say that recent advances will lead to new discoveries that will far outweigh any concerns.
"Anytime a new research field emerges, it takes a while to put the basic building blocks together. It's just a matter of time. We're getting there," said S.K. Gupta, a mechanical engineering professor at the University of Maryland who teaches a bio-inspired robotics course.
"If you think about true biology, sensing and actuation are working at a really, really small scale," he said. "Thirty years ago we weren't able to construct anything at the micro scale. I think recent advances that are taking place in the area of micro-fabrication will help us tremendously."
Research could one day unlock the mysteries of the incredible tensile strength of spider silk, the way organisms propel themselves through water and air so much more efficiently than vehicles, and how the fluids secreted by marine organisms have greater bonding strength than any glue humans have produced.
Even the smallest creatures could hold a compelling secret.
"Every organism is designed to solve a problem," Weissburg said.