We start out postulating sharp boundaries, such as between humans and apes, or between apes and monkeys, but are in fact dealing with sand castles that lose much of their structure when the sea of knowledge washes over them. They turn into hills, leveled ever more, until we are back to where evolutionary theory always leads us: a gently sloping beach.

The Age of Empathy: Nature's Lessons for a Kinder Society (ed. Crown, 2009) - ISBN: 9780307462527