About 27 humanoid species roamed the Earth since splitting off from their ape ancestors 7 million years ago; more are turning up, but only one remains. Science journalist and former CNN bureau chief Walter (Thumbs, Toes, and Tears: And Other Traits That Make Us Human, 2006) delivers a mixture of fact, research and conjecture that describes how this happened.
Anthropologists define humans as primates who walk upright, but the author focuses on another fundamental, if bizarre, difference—human species deliver children prematurely. Traditionally, teachers explain that this allows passage of our increasingly large skull and brain through the birth canal, but there is more to it. We are not only born as fetuses, but we keep infantile ape features (near-hairlessness, flatter faces, higher foreheads, a straight big toe) into adult life. Carrying the analogy further, Walter emphasizes that humans not only have an extended physical childhood (gorillas reach adulthood at 11), but we preserve the mental qualities of childhood: curiosity, adaptability, and the love of play, new experiences and experimentation. Our victory was not preordained, and three other brainy species shared the planet when the first Homo sapiens appeared 200,000 years ago. The first breakthroughs, tools and fire, occurred over 1 million years earlier, and we did not seem an improvement. More than another 100,000 years passed before Homo sapiens’ burgeoning neural connections passed a tipping point that produced the language, culture, creativity and technology that enabled it to rule the world. The author offers a short epilogue about the “next human,” writing, “short of another asteroid collision or global cataclysm, we will almost certainly become augmented versions of our current selves.”
Walter never explains precisely why our species stands alone, but few readers will complain at the end of this engrossing, up-to-date account of human evolution.