For the last 2,500 years, since Herodotus and Thucydides pioneered the Western tradition of history, the discipline has been one of the load-bearing intellectual foundations of our culture. In 1905, the philosopher George Santayana famously stated that those “who cannot remember the past are condemned to repeat it.” Long before this, Western civilisation had taken a particular interest in its past, not just for matters of intellectual curiosity, but for the lessons it can teach us. Suetonius’s The Twelve Caesars makes clear its author’s belief that the private character of a Roman autocrat redounds to the health of the Roman state. From the bold Caesar to the perverse Caligula, Suetonius showed how the past could teach us to rule in the present and future.

Over the last few centuries, this venerable tradition of studies of character and the recitation of the annals of diplomacy and war, drawing upon a corpus of textual records, has matured into one of the established social sciences. Modern scholars bring analytic rigour, pretensions to prediction, and empirical tools from economics, anthropology, and archaeology, transforming history from a distillation of textual memory to a reflection of multiple lines of evidence that can echo back through the centuries, and even millennia. New techniques have affected even the time-tested analysis of text: the Vesuvius Challenge aims to deploy computational visualisation and analysis to read the carbonised Herculaneum scrolls without opening them. In the future, textual historians may ponder the nuances of machine-learning algorithms as much as they do the translation of texts and the location of obscure archives.

Of history’s helpmates, archaeology, which grew out of 19th-century antiquarianism, has arguably been the longest-lasting collaborator, taking a humanistic endeavour and making it part of a broader movement of the “historical sciences.” But in the 21st century, the injection of the methods and means of genetics—a hard science of the 20th century—into an enterprise that goes back to Herodotus’s chronicles of the Persian Wars has been the most rapid and striking transformation, with an explosion of findings settling questions old and posing others new.

If the primary instrument in the toolkit of the 20th-century historian was their familiarity with archives of long-forgotten texts, supplemented with the material information proffered by archaeologists, 21st-century historians can now avail themselves of an entirely different text: the DNA sequences of individuals present and past. Whereas historians of the past relied on letters and texts to flesh out the biography of a single person, laboriously making societal judgements from the aggregate of these individuals, historians today can infer the history of an entire population from the genetic code, the physical substrate of which is the biomolecule deoxyribonucleic acid, or DNA. The Jesuits would say, “Give me a child until he is seven and I will show you the man.” Today, scientists can ask for someone’s genome, and they will show you that individual’s entire genealogical history.