For nearly 50 years, engineers worldwide have been trying to build humanoid robots capable of stable and efficient walking as humans do. While creditable progress has been made, they are still far from achieving that goal.
Even just to satisfactorily emulate only one of the body's joint-and-muscle systems used in walking—i.e. the ankle/foot complex, or the knee, or the hip/pelvis complex—presents huge engineering challenges.
An ideal robotic foot for example, as a recent review paper pointed out, would have at least these three human characteristics: a flexible heel (shock absorption), toe flexion (energy efficiency, staying upright when standing still), and a flexible arch capable of being stiffened at critical points during each stride (energy harvesting—mimicking the windlass mechanism of the human foot—and shock absorption).
Meanwhile a robotic ankle needs to be able to store, and release, energy at appropriate times during each stride, to attain the energy efficiency of the human ankle.
What's the progress so far towards implementing these features of the ankle/foot complex? "Due to their technical complexity," the review paper laments, "all these human-like properties are still not available in one single ankle–foot solution."1
But the original design just evolved out of nothing, without a Designer? Too hard to believe.
1. Torricelli, D. and 9 others, Human-like compliant locomotion: state of the art of robotics implementation systems, Bioinspir. Biomim. 11(5):1002, 22 August 2016.