Unearthing Ancient DNA: Rewriting the Story of Human Evolution

In December 2013, the world witnessed the discovery of the oldest evidence of human development, prompting profound questions in the field of evolution. Unearthed from the 'pit of bones' in a northern Spanish underground cave, a femur (thigh bone) fossil unveiled remarkable insights. This femur, painstakingly retrieved by scientists who had previously collected twenty-eight nearly complete human skeletons in the same cave since the 1970s, yielded mitochondrial DNA (mtDNA) dating back approximately 400,000 years—an astonishing 300,000 years older than any prior humanoid DNA sample.

Homo heidelbergensis, an extinct species that once inhabited Europe, Africa, and western Asia, potentially dating back as far as 1.3 million years ago. This species pioneered life in colder environments and could have been among the earliest to engage in burial practices.

Initial observations of the femur's anatomy suggested a resemblance to Neanderthals. However, a comprehensive analysis of the DNA evidence revealed a closer genetic connection to the Denisovans, whose DNA had previously been extracted from remains discovered in Siberia, situated some 4,000 miles to the east. This revelation challenged the prevailing narrative of human development, rooted in existing fossil findings and DNA analyses. Until then, it had been generally accepted that humans, Neanderthals, and Denisovans shared a common African ancestor some 500,000 years ago. This ancestral population, after diverging from humans, migrated out of Africa and split once more, approximately 300,000 years ago, giving rise to the Neanderthals in Europe and the Denisovans in the east. Meanwhile, our human ancestors remained in Africa, eventually evolving into Homo sapiens. These Homo sapiens migrated to Europe and Asia 60,000 years ago, where they interbred with both Neanderthals and Denisovans, ultimately leading to the extinction of these two groups. However, the new DNA evidence raised a perplexing question: Why were Denisovan fossil remains found in Spain?

These groundbreaking DNA revelations were made possible by advancements in the retrieval of ancient DNA. When a biological organism perishes, its DNA disintegrates into small fragments, which over time intermingle and become contaminated with DNA from other sources, particularly soil bacteria. In 1997, Svante Pääbo, a Swedish biologist specializing in evolutionary genetics, and also affiliated with the Max Planck Institute, pioneered a novel technique for extracting DNA fragments. This breakthrough method enabled him to decode the genome sequence of the Neanderthal in 2010 and the Spanish femur. Such remarkable progress hints at the potential to reshape our understanding of biological history.