We are separated from our nearest relatives, the chimpanzees, by only one or two percent of our genes – but also by some 6 million years of going our different evolutionary ways. So when we meet the eyes of a chimp we are reminded uncannily – and perhaps a little uneasily – of ourselves. But we are also aware that behind those eyes is a mind very different from our own. Alan Alda sets out to explore that difference, and quickly finds that the scientists studying chimps and other non-human primates are themselves separated into opposing worldviews. One camp emphasizes the continuity between us – seeing everything we believe to be uniquely human present in at least a rudimentary form in our ape and even monkey cousins. The other camp sees a sharp discontinuity in our abilities, admiring chimps for their superb adaptation to their (rapidly disappearing) forest environment, but also granting to human minds a special status that has enabled us to conquer the planet (and cause those forests to disappear).

In visiting with chimps and those who study them, Alan challenges the arguments of both sides in the debate. Yes, chimps exhibit empathy for others in their group; is that the same empathy humans show for victims of a far off natural disaster? Chimps have cultural practices they pass on within their social group; are those cultures the same as the cultures that can separate humans into “us” and “them?” Chimps can easily tell the difference between heavy and light, but do they have a concept of heavy and light? Chimps use tools, and can be taught that symbols represent objects; does that mean they have technology and language? Chimps can cooperate on tasks that reward them with food. Is that the same cooperation humans employ to build a skyscraper or rescue the victims of an earthquake or even agree to take a walk together? Chimps and monkeys both seem able to judge the intentions of others. Does that mean they wonder, and worry, about who is saying what about whom, and why? And what about that one or two percent change in our DNA? Do those figures mask not a tiny difference but an evolutionary chasm?

In short, how much of the Human Spark flared only since we evolved away from our non-human primate cousins, and how much was already there at the parting of the ways?