In Spain’s Atapuerca Mountains, the Sima de los Huesos – the Pit of Bones – archaeological site has been a treasure trove of data on early human ancestors for years. On December 4, 2013, a study by Matthias Meyer and team from the Max Planck Institute for Evolutionary Anthropology was published online in Nature, detailing a recent project to extract and replicate the DNA of an ancient leg bone from the site. The skeletons from the site look as though they belong to Neanderthals, and scientists have previously classified them as homo heidelbergensis, possibly a forerunner to modern humans. The results of the DNA analysis were surprising: rather than the bone belonging to a Neanderthal, as expected, the DNA more closely resembled a Denisovian, another early human type previously thought to have only lived in Asia. The DNA test also dates the leg bone at 400,000 years old, meaning that researchers have beaten the previous record for the oldest human DNA by 300,000 years.
Working on a paper for your evolutionary biology or archaeology classes? Consider these good research paper topics:
- Archaeological efforts at Sima de los Huesos
- Denisovians, Neanderthals, and other early humans
- DNA sequencing and analysis as used in archaeology
- Techniques for isolating DNA
Sima de los Huesos
Atapuerca has two remarkable historical sites very close together, Sima de los Huesos – sometimes just called Sima – and Gran Dolina, which has bones that may date to 800,000 years ago. Both contain the remains of hominids, or early human relatives. Both sites have been important to developing a better picture of human evolution.
In a Natural History article from 2003, “An interview with Ian Tattersall,” Tattersall, the co-curator of an exhibit called “The First Europeans: Treasures from the Hills of Atapuerca,” explained Sima’s importance: “Human fossils are not that common and this particular site is the most astonishing concentration of human fossils that has been found anywhere in the world.” He described the site’s location as “hellish,” and said: “You have to walk 700 yards into a cave through dark passages in the pitch dark and over a rough floor. And then you have to descend 50 feet vertically down a shaft in the dark ‘til you come to a slope that leads down even further into the cavity where these bones collected.”
It’s that environment in which Meyer and his team began uncovering the data about the genetics of these early humans.
Denisovians, Neanderthals, and changing understanding of human evolution
Before the DNA analysis was conducted by Meyer and his team, the accepted understanding of human evolution was that the direct ancestors of modern humans were shared by other, now extinct human groups, such as the Neanderthals and the Denisovians. These branches of early humanity were thought to have split about 300,000 years ago, with Neanderthals going into Europe, Denisovians heading east, and the ancestors of modern humans remaining in Africa.
Denisovians are a fairly recent discovery. Identified from remains in Siberia, the Denisovians were classified based on distinctions in their DNA. In 2012, Meyer and his team extracted DNA from a little finger and two molar teeth of a Stone Age girl from the Siberian site, and used a then-new technique to sequence her genome repeatedly in order to eliminate error and develop a clear picture of her complete DNA sequence.
Meyer and team used the same type of technique on the leg bone from Sima. Malcolm Ritter of the Huffington Post, writing in “DNA from bone of human ancestor is oldest of its type, dates back 400,000 years,” offered a lay-view of the process: “The researchers mapped almost the complete collection of so-called mitochondrial DNA. While the DNA most people know about is found in the nucleus of a cell, mitochondrial DNA lies outside the nucleus. It is passed only from mother to child.”
Given the assumption that the early hominids in Europe were most likely Neanderthals, and because the bones resembled Neanderthal skeletons, Meyer and team expected the DNA to be most similar to the Neanderthal tree. Instead, the DNA showed a close relation to the Siberian remains, 4,000 miles east of Sima.
What does this mean? “Right now, we’ve basically generated a big question mark,” Meyer said, as reported by Carl Zimmer in the New York Times article “Baffling 400,000-year-old clue to human origins.” Some ideas the researchers are suggesting include:
- The humans at Sima had both Neanderthal and Denisovian ancestors.
- The newly discovered DNA once existed in both Neanderthals and Denisovians, but was replaced by other variants in Neanderthals.
- The bones at Sima belong to a unique branch of humans, possibly related to homo erectus.
What do you think the bones from Sima tell us about human history? Tell us in the comments.