organisms have evolved over billions of years to take advantage of passive dynamics, which is basically the application of newtonian physics to what is mostly a mechanical design problem. we've known for a long time that passive dynamic elements are not only energetically more efficient, but also makes computations simpler.

by contrast, active dynamic locomotion is akin to putting a joint between the front fork of a bike and the shaft, and installing a hand pump that you have to constantly actuate to keep the bike stable while you're riding it. you could do it, but it's not the best solution.

By the same token, most of the tooling and parts for building airplanes isn't all that useful for building orinthopters.

So it's not just knowledge. It's knowledge expressed in the form of industrial infrastructure and products.

This isn’t a kinematics homework where you can draw the links and joints and get full marks. You have to actuate them. For a human gait, you need to generate the same torque, at the same velocities, and the mass of the actuator needs to distribute across the linkages in the same proportion. Guess what? Actuators like that are hard to find.

I should paraphrase that for interviews. "This isn't a CS homework where you can cite Big-O and get full marks. We have to be able to implement code that uses them."

And by that, I don't mean that you have to write all of the actual code. But one needs to be able to specify it exactly so someone could implement it and know enough about that to tell someone of the pitfalls in the current problem context/framework.