New fossil finds and technological breakthroughs in collecting and decoding ancient DNA are re-writing the history of human evolution, often with shocking and surprising results. As developments continue apace, what could be uncovered next?
“Ours, it turns out, is a repeated history of migrations and mixing,” says Cosimo Posth, a junior professor of archaeo- and palaeogenetics at the University of Tübingen in Germany. “Much of what we thought we knew about human history – that populations lived for centuries mostly without mixing – was overturned thanks to modern-day genomics.”
In March 2023, Posth and his colleagues analysed the largest ever ancient genetic data set (356 – including 116 from new-found remains in 14 countries) of prehistoric hunter-gatherers, from which they derived new insights about the groups’ migration and survival.
A mere decade or so earlier and their work wouldn’t have been possible. Breakthroughs in collecting and deciphering ancient human DNA during this time have rapidly accelerated discoveries about the origin of our species – Homo sapiens – often, re-writing history.
“These technologies have enriched the field tremendously,” says Chris Stringer, a British anthropologist at the Natural History Museum who has worked in the field for over 50 years. “They’ve given us so much more information and they’re developing all the time.”
It all started at the turn of the century. Revelations started to come thick and fast following a major breakthrough in ancient genome sequencing, explains Stringer.
Back then, it was thought human evolution over the last 500,000 years was fairly well understood. It was believed to begin with Homo heidelbergensis, known to be from Africa and western Eurasia between about 600,000 and 400,000 years ago. These gradually evolved into Neanderthals, in western Eurasia, and Homo sapiens, in Africa.
Our species later dispersed from Africa, about 60,000 years ago. By around 30,000 years ago, we had completely replaced the ‘inferior’ Neanderthals across Eurasia, with little or no interbreeding.
Or so it was thought. Then, in the mid-1990s, Swedish geneticist Svante Pääbo deciphered a relatively short component of mitochondrial DNA from a Neanderthal male. A feat that seemed like “science fiction” at the time, says Stringer.
“No one could have imagined that in ten years we’d have whole genomes from fossils.”
But that is exactly what happened. By 2010, off the back of advances in genome sequencing for healthcare and medicine, Pääbo drafted a whole genome of a Neanderthal. This, and subsequent work, demonstrated – rather shockingly – that Neanderthals and other extinct hominids made a significant contribution to our ancestry.
In other words, Homo sapiens did interbreed with other species living at the time and humans have inherited about 2 per cent of their DNA from Neanderthals.
Other discoveries and revelations followed: that of a previously unrecognised kind of human, the Denisovans, from a whole genome recovered from a finger bone fragment found in a Siberian cave. That the arrival of Homo sapiens in Europe was 150,000 years earlier than previously understood was confirmed by the dating of a fossil found in Greece in 2019.
Being able to sequence ancient human DNA has been game-changing, but working with it is vastly different from that of modern humans, explains Dr Matthias Meyer, a biochemist who was part of Pääbo’s group developing those early breakthroughs. He is now head of the Advanced DNA Sequencing Techniques group at the Max-Planck-Institute for Evolutionary Anthropology.
Ancient DNA typically has chemical modifications, is extremely short, and often only small quantities are recoverable, making it very difficult to extract from a biological sample for processing by a sequencer. For example, DNA from blood can produce thousands to millions of DNA base pairs, compared to around 40-60 from ancient DNA.
Heidi Vella 