Many of the skeletons are several thousand years old. The inferences come from combining data from genome sequences of contemporary people with those extracted from skeletal remains. The second section of the book presents a historical survey of people living in different continental regions. Australopithecines were also unanticipated, and this finding ultimately restructured our thinking about human origins. The importance of discovering the Denisovans approaches that of Raymond Dart's discovery of australopithecine fossils.

The Denisovan genome shows how an ancient genome can reveal a previously unknown, and unanticipated, member of our lineage. The possession of a Neanderthal genome sequence is an awesome achievement insofar as Neanderthals were the first fossils to shed light on human evolution. As a core member of this team, Reich contributed statistical analysis. Our knowledge of both genomes resulted from the work of a research team led by the evolutionary geneticist Savante Pääbo. This section then describes the Neanderthal and Denisovan genomes. The first begins by reviewing the basics of DNA's structure and the genetic principles that allow inferences about ancestry from variations in the sequences of nucleotides in DNA. The book is divided into three main sections.

However, Reich is prone to overstate his case in ways that will infuriate some readers for example, Chapter 1 is titled 'How the Genome Explains Who We Are.' His prose is readable, and he has avoided overuse of jargon and highly technical terms. He has written a personalized account that will interest a wide audience that includes both professionals and the lay public. The author, David Reich, is a primary innovator in this new field of study. Today, these data are flooding in, and they are contributing a new dimension to our investigations of prehistory. Twenty-five years ago the idea of DNA extracted from the remains of long dead beings was science fiction. David Reich's book Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past (New York: Pantheon Books, 2018 xxv+335 pp.) is a landmark synthesis of findings from studies on DNA sequences collected from the bones of ancient people.

Who we are and how we got here review