The World Before Us

The book opens with one of the most important moments in the author's life: Monday 22 June 2015, 9.10 a.m., in an Oxford lab. Together with student Samantha Brown, the author touches for the first time a 2.4-centimetre bone from a human who lived around 120,000 years ago. It later turns out to belong to the only “first-generation hybrid” human ever found: a young girl whose mother was a Neanderthal and whose father was a Denisovan. The introduction sets out the book's thesis: over the last 300,000 years five, six or even more types of human lived on Earth — so why are we the only ones left?

Chapter eight tells step by step how this discovery happened, and it is the book's best chapter. The problem is simple: 95% of the bones from Denisova Cave have been broken up by scavengers and cannot be assigned to any species — “worthless” fragments sitting in plastic bags in storerooms. At a 2014 meeting in the Altai, the author and archaeologist Katerina Douka — research partner and spouse — propose a new method: ZooMS (zooarchaeology by mass spectrometry). Collagen protein is extracted from each bone and its peptide sequence is compared, like a “molecular fingerprint”, with a library of known species.

The chapter is very honest about the ratio of romance to drudgery in science. Samantha Brown, a master's student from Australia, spends weeks in the lab's cutting room, first sampling more than 700 bones, then 1,308 more from a new bag brought back from Russia. The first results show only bear, cow, deer, dog, fox, mammoth and other animals. When the author says “that's enough, write your thesis”, Samantha says “No!” and wants to keep going. Finally, on a Friday evening, sample DC1227 shows a hominin spectrum. The author's all-caps, expletive-laden email sent at that moment is printed as it was, and it beautifully shows the human side of discovery.

Then the story unfolds like a detective novel. Samantha names the bone “Denny”. It weighs 1.68 grams, comes from Layer 12 and is older than 49,900 years. At the Max Planck Institute in Leipzig, Svante Pääbo's team first finds Neanderthal mitochondrial DNA — the mood dips a little, since everyone hoped for a Denisovan. But months later the nuclear DNA gives an unexpected result: roughly half the genome is Neanderthal and half Denisovan. CT scans show the bone belonged to a girl at least thirteen years old. Published on the cover of Nature in August 2018, the discovery becomes one of the biggest science stories of the year.

The chapter's scientific argument matters too. The author admits that finding Denny was a huge stroke of luck: if such hybrids had been common, Neanderthal and Denisovan genomes would not have stayed distinct. Yet Denny's genome shows more: the father's ancestry also carries Neanderthal admixture from hundreds of generations earlier, and the mother is more closely related to the Neanderthals of Vindija Cave in Croatia than to the other Neanderthals in the cave. So human groups met and mixed not once but many times — which calls the very notion of “species” into question.

The style is lively and sincere; the author presents colleagues — Svante Pääbo, Anatoly Derevianko, Michael Shunkov — as people and doesn't hide the rivalry and the race to publish first. A weakness is some of the technical material, such as Sanger sequencing and collagen ultrafiltration: important, but tiring for non-specialists. Even so, this is one of the clearest accounts of how our picture of human origins has changed over the past decade.

• Vivid, first-hand accounts of discoveries from the inside
• Complex genetic and dating methods explained with diagrams
• An honest portrayal of collaboration and rivalry in science