It continues today, which is why we have “Quest: The Essence of Humanity,” an excellent new book in which biochemist Charles Pasternak plays Plato. He begins by recounting the four traits most anthropologists point to as distinctly “human”: bipedalism, agile hands, sophisticated vocal cords and big brains. But they aren’t enough alone; each has a proverbial plucked chicken of its own among the animal kingdom. The crucial difference, Pasternak argues, is how we’ve used those gifts in the service of our curiosity–and how they’ve helped us conquer the globe. “All organisms search for food and mates,” he says. “But we search for purely intellectual reasons. We’re constantly tinkering. We can’t stand still.” One might say the same for Pasternak’s prose, as wide-ranging as the human species itself, skipping from DNA to Minoan civilization to GM crops in search of evidence. Though Pasternak says the word “manifesto” is “a bit too strong,” the book clearly is one, even daring to predict the decline of the West (our dumbed-down society discourages “questing,” says Pasternak). Out in his native England for several months, the book has already caused a stir and has its own Diogenes, philosopher Mary Midgley–which means the quest for the definitive answer is probably still on.