Trees. Trees protect many animals, including our recent ancestor, the chimpanzee. But like the ocean, trees can be turbulent. It's possible that evolution favored the species that kept their aversion to motion, as they moved to lower, less mobile branches, so reducing their risk of falling to their death. Humans may think they've left trees and swaying branches behind, but the tall buildings we like to live and work in have a tendency to sway silently in the wind much as trees do, with some people sensitive to motion sickness reporting dizziness, loss of concentration, drowsiness, or nausea.