A Brief History of Everyone Who Ever Lived

Geneticist and science writer Adam Rutherford argues that DNA has become a revolutionary historical source, one that complements and sometimes overturns what archaeology, written records, and oral traditions have long told us about who we are and where we came from. He opens by observing that approximately 107 billion modern humans have ever existed, all closely related through a single African origin. Because the number of ancestors each person has doubles with every generation going back, pedigrees inevitably fold in on themselves, meaning all humans are enmeshed in a tangled web of shared ancestry rather than a neat family tree. The genome, a three-billion-letter record unique to each individual, now serves as a text to read alongside older historical sources. Rutherford acknowledges the field's troubled origins, noting that human genetics was born synonymous with eugenics—the idea of improving the human population through selective breeding—and warns that the culturally pervasive idea of genes as destiny is a fallacy the book repeatedly confronts.

In the book's first half, Rutherford rewrites human prehistory through genetics. He challenges the iconic linear image of apes evolving step by step into modern humans, arguing instead that our evolutionary history resembles a messy, tangled shrub. He traces the landmark 1997 extraction of mitochondrial DNA, a small loop of DNA inherited only from mothers, from the arm bone of Neanderthal 1, a specimen discovered in a German cave in 1856, by Swedish researcher Svante Pääbo. This work inaugurated the field of paleogenetics, the study of DNA from ancient remains. By 2010, Pääbo's team had assembled a complete draft of the Neanderthal genome, revealing that modern humans and Neanderthals interbred repeatedly, beginning at least 100,000 years ago. Most non-African people alive today carry a small percentage of Neanderthal DNA as a result.

Rutherford then introduces the Denisovans, a third human species identified in 2010 entirely through DNA extracted from a single finger bone found in a Siberian cave. Up to five percent of the genomes of contemporary Melanesians, the Indigenous people of islands near Australia, derives from Denisovans. The Tibetan gene EPAS1, which aids survival at high altitude, also appears to have been acquired from them. Rutherford concludes that whenever ancient human groups encountered each other, they had sex, and the Neanderthals and Denisovans never truly went extinct but merged into us.

Turning to the origins of modern Europeans, Rutherford describes a 2015 study led by Harvard geneticist David Reich that extracted DNA from ancient individuals and compared them to thousands of living Europeans. The results show that modern Europeans descend from three distinct ancestral populations: the original hunter-gatherers, eastern farmers who migrated into Europe between 9,000 and 7,000 years ago, and the Yamnaya, pastoralists from the Russian Steppes who arrived around 5,000 years ago. He uses lactase persistence, the genetically determined ability to digest milk into adulthood, as a case study of gene-culture coevolution: A single DNA change near the lactase gene spread through dairy-farming communities roughly 5,000 to 10,000 years ago. He also traces the recent evolution of pale skin and blue eyes, showing through ancient genomes that dark skin persisted among European hunter-gatherers as recently as 8,000 years ago. In a striking application of paleogenetics to epidemiology, Rutherford describes how scientists extracted DNA of Yersinia pestis, the bacterium that causes bubonic plague, from ancient teeth, confirming that both the sixth-century Plague of Justinian and the 14th-century Black Death originated in China and that plague existed in Europe as early as 5,700 years ago, potentially reshaping European immune genes through natural selection.

Rutherford devotes extensive attention to the peopling of the Americas, explaining that the founding population crossed from Asia via Beringia, a land bridge exposed by lower sea levels during the last Ice Age, remained isolated for roughly 10,000 years, and then spread throughout both continents. He recounts the politically fraught stories of Anzick-1, a 12,600-year-old toddler buried with stone tools characteristic of the Clovis culture, whose genome confirms a single founding population, and Kennewick Man, an 8,500-year-old skeleton from Washington State whose ownership sparked a 20-year legal battle between scientists and Native American tribes. DNA analysis ultimately confirmed Kennewick Man was most closely related to living Native Americans. Rutherford critiques companies that sell DNA tests claiming to determine tribal membership, arguing that no genetic marker is exclusive to any tribe. He discusses the damaged relationship between geneticists and Indigenous communities, citing the case of the Havasupai tribe, whose blood samples, given for diabetes research, were used without adequate consent for unrelated studies.

In a chapter on royalty and ancestry, Rutherford presents mathematician Joseph Chang's calculation that every European alive 1,000 years ago who left descendants is the ancestor of every living European today. He uses this finding to critique commercial genetic ancestry companies, which University College London geneticist Mark Thomas describes as practicing "genetic astrology": selling emotionally appealing but scientifically hollow narratives about Viking or royal descent. Rutherford contrasts this with the meticulous 2012 identification of King Richard III's skeleton beneath a Leicester car park, where mitochondrial DNA matched two living maternal-line descendants. He also examines the Hapsburg dynasty's catastrophic inbreeding: Charles II of Spain, the last Hapsburg ruler, had an inbreeding coefficient higher than that of a child born to siblings, resulting in severe physical and intellectual disabilities and the end of his line.

The book's second half addresses what genetics reveals about living humans. Rutherford argues forcefully that race does not exist as a scientifically valid genetic category. He traces the intellectual roots of scientific racism through Francis Galton, Charles Darwin's half-cousin, who coined the term "eugenics" in 1883 and whose ideas led to forced sterilization programs in 31 US states and underpinned Nazi atrocities. He presents Harvard biologist Richard Lewontin's landmark 1972 finding that 85 percent of human genetic variation occurs within so-called racial groups, not between them, and shows that subsequent genomic studies confirm this pattern.

Rutherford then tackles the gap between what genes promise and what they deliver. The Human Genome Project revealed that humans have only about 20,000 protein-coding genes, far fewer than expected. Genome-wide association studies (GWAS), which scan hundreds of thousands of genetic variants across large populations, have shown that complex traits and diseases are influenced by many genes of individually tiny effect. The predicted genetic contribution from twin studies consistently exceeds what researchers can find in DNA, a puzzle known as "missing heritability." He extends this argument to criminal behavior, describing the case of Davis Bradley Waldroup, whose charge was reduced from first-degree murder to voluntary manslaughter after his defense cited the MAOA gene, often called the "warrior gene." While certain MAOA variants correlate weakly with aggression, Rutherford contends that using a single gene to mitigate criminal responsibility is a dangerous form of biological determinism.

Rutherford also examines epigenetics, the study of chemical modifications that silence genes without altering the DNA sequence itself. He describes the Dutch Hongerwinter of 1944–1945, when a Nazi food embargo starved the western Netherlands. Children conceived during the famine were born smaller and, as adults, experienced higher rates of obesity, diabetes, and cardiovascular disease. Their children also showed effects, suggesting transgenerational transmission, though Rutherford cautions that these changes fade after a few generations and do not constitute a rewriting of the genetic code. He criticizes New Age appropriations of epigenetics that overstate its significance, treating it as though individuals can consciously reshape their own DNA.

On whether humans are still evolving, Rutherford answers unequivocally yes. A 2013 study found that three-quarters of more than a million genetic variants in 6,500 genomes arose in the last 5,000 years. Modern medicine has weakened natural selection's grip, yet as long as there is heritable variation in reproduction and survival, selection retains some purchase. He concludes that every living human is a transitional form, and that the genome is an incomparable historical text, one that will never be fully read because, as long as there are people, our exploration of it will never end.