In Marlows voyage down the african coast, he observes people with "wild vitality." what does he mean

I read this awhile ago, but basically Marlow was describing the difference between the European and the indigenous men of the Congo as stark and absolute. Travelling down the river Marlow observes a "wild vitality, an intense energy of movement, that was as natural and true as the surf around their coast”. Conrad was trying to point out the authenticity, savage and alive nature of these men. They were a true reflection of their environment. Contrast the European man who was tame and predictable. After European contact and influence Marlow will notice quite the different in the indigenous people. It is a transformation that is sad.