What two arguments does the author make as to why wheels may not be as advantageous for other animals as they are for "human animals"?

For a wheel to be useful you need to have a network of smooth surfaces $($AKA roads$)$ to use it on$.$

Other animals' legs, either $4-$legged or $2-$legged, are already much better than our legs, so a wheel would not be much more of an improvement.

In the past, animals $($such as horses$)$ generally pulled wheeled vehicles so wheels just slowed them down.

A wheel, when paired with an engine, will always beat leg$-$power, but because animals don't have mechanical engines there is no benefit to having a wheel.