Right. And carrying weight was and is beneficial and unique to humans. I.e., the human evolved to carry and is built in a way that favors carrying.

No other mammal can carry for distance. Four legged animals can’t carry well. (Unless, like pack animals, a human straps the weight onto them.) They have to carry or drag items with their mouth, which they can’t do for any appreciable distance.

Primates are unique because we can carry stuff in our hands while we cover ground with our feet. Monkeys generally suck at this, though. They tend to carry short distances, because for them the act is highly inefficient. It costs a chimp 75 percent more energy to walk the same distance as a human. Ants are bugs.

The book will shed more light on this, if you are interested.