Thumbs, Toes, and Tears: And Other Traits That Make Us Human

Walker Books, 2006

The fascinating evolutionary links between six seemingly unremarkable traits that make us the very remarkable creatures we are.

Countless behaviors separate us from the rest of the animal kingdom, but all of them can be traced one way or another to six traits that are unique to the human race―our big toe, our opposable thumb, our oddly shaped pharynx, and our ability to laugh, kiss, and cry. At first glance these may not seem to be connected but they are. Each marks a fork in the evolutionary road where we went one way and the rest of the animal kingdom went another. Each opens small passageways on the peculiar geography of the human heart and mind.

Walter weaves together fascinating insights from complexity theory, the latest brain scanning techniques, anthropology, artificial intelligence, cognitive psychology, and robotics to explore how the smallest of changes over the past six million years – all shaped by the forces of evolution -- have enabled a primate once on the brink of extinction to evolve into a creature that would one day create all of the grand and exuberant edifices of human culture.

As the story of each trait unfolds, Walter explains why our brains grew so large and complex, why we find one another sexually attractive, how toolmaking laid the mental groundwork for language, why we care about what others think, and how we became the creature that laughs and cries and falls in love. Thumbs, Toes and Tears is original, informative, and delightfully thought-provoking.

Notes from the author:

I was at a conference in the early 2000s that was all about the future and the coming trends in computer science. There were lots of panel discussions about how to create software and hardware that would be easy for people to use. The same was true of artificial intelligence (AI). How could scientists best create machines that related to humans. As I watched this, it occurred to me that there was no way we could ever create really useful technologies for people if we didn’t first truly understand what made us the way we are. To create really useful machines, we first had better get a handle on what made us humans tick.

That was when I came up with the idea for Thumbs, Toes, and Tears. I knew that getting to the bottom of human behavior was a big undertaking so I looked instead into what traits had we evolved that were unique to us, completely different from other animals. And how had the evolution of those traits shape our humanity? Maybe if we could understand a handful of those things, I—and readers—could wrap their minds around the forces that created us.

After a lot of research, I came up with six: the opposable thumb, our big toes, our very odd voice boxes (pharynx), laughing, crying and kissing. I learned a lot. If you read the book, I hope you’ll find it as interesting as I did.

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