In the last few years, a startling new message has emerged about our biology. Scientists probing the deep workings of organisms have discovered that all living things, from yeasts to worms to humans, are guided by similar genes and proteins, which have passed down nearly intact for hundreds of millions of years. At the most fundamental level, humans are genetically linked to every part of the natural world. The award-winning science writer Jennifer Ackerman brings these astonishing discoveries together for the first time, weaving a mesmerizing story of heredity that is only now being understood.