Over the decades, research has chipped away at our most cherished ideas about human specialness: it turns out that we share such things as theory of mind, empathy, and time perception with many other creatures.
But there is one feature of humanity that we can claim to be uniquely our own. Animals – unless captured by humans or infected with zombie parasites – tend to act staunchly in their own interests. Why is it that this frog or that bat or this humming-bird behaves in the peculiar way it does? The answer is almost always the same: to further its survival and the propagation of its genes.
