“Safina explains how an evolutionary understanding of the emotions helps us to see even humble creatures as individuals. The chemical oxytocin creates feelings of pleasure and a craving for sociality. So widespread is it that it must have originated 700 million or more years ago. Serotonin, a chemical associated with anxiety, is probably equally ancient: crayfish subjected to mild electrical shocks have elevated serotonin levels, and act anxiously. If treated with chlordiazepoxide (a common treatment for humans suffering from anxiety) they resume normal behavior.”