Human beings tend to be anthropocentric. That is, we often see ourselves as evolution's magnum opus despite the fact that, as biomass goes, we're insignificant compared to plants and other animals. For instance, scientists estimate that there are more than three trillion trees on Earth—a number that even dwarfs the amount of stars in our galaxy. And when you add the populations of the more than 380,000 other plant species, the total becomes mind-boggling. Nonetheless, many of us assume that we're the smartest, most conscious beings on Earth. But what if consciousness isn't a feature limited solely to humans—and what...