In his new book, science journalist Carl Zimmer explores the many factors, from genetics to microbes to environment, that we inherit from our ancestors to make us who we are. As the study of genes becomes more accessible and comprehensive, scientists have come to realize that our genomes are not just a simple matter of inheriting material from mom and dad, but rather our DNA is patched together from numerous sources tracing back along divergent ancestral lines. The genetic result is often as intricate and multifaceted as an individual’s personality, and DNA is only the groundwork of our hereditary traits. As cells multiply to constitute our bodies and bacteria cultivates in our guts, we take more than just strands of DNA from those who came before us—and that’s to say nothing of the environmental factors that shape our minds and bodies. With a prescient look at today’s leading research, Zimmer explores what we know about heredity and what we still have to learn.