Animals and machines work differently, and the solutions that work best for one group seldom work best for the other.

Examples:

No animals have locomotion by means of wheels, but wheels are clearly the best way to cover almost all terrain quickly.

Birds flap their wings, but no commercially successful machine has ever operated on that principle because it simply is not suitable for machine.

If one wishes to reduce fatigue of soldiers, the most sensible solution is a small armored vehicle, like the armored version of the Hummer, or even a smaller, one-person vehicle. Arms and legs are just not the way to go.

Hell, even a motorcycle gives greatly increased mobility but no protection.

David F Mayer

http://www.globalsecurity.org/military/systems/ground/lav.htm