" It is important none the less that our remotest identifiable ancestors lived in trees because what survived in the next phase of evolution were genetic strains best suited to the special uncertainties and accidental challenges of the forest. That environment put a premium on the capacity to learn. Those survived whose genetic inheritance could respond and adapt to the surprising, sudden danger of deep shade, confused visual patterns and treacherous handholds. Strains prone to accident in such conditions were wiped out. Among those that prospered (genetically speaking) were some species with long digits which were to develop into fingers and, eventually, the oppositional thumb, and other forerunners of the apes already embarked upon an evolution towards three-dimensional vision and the diminution of the importance of the sense of smell. "

― , The New Penguin History of The World