The growing human family
The human genome contains traces of two ancient relatives – Neanderthals and Denisovans
Homo sapiens is not the only species to have migrated out of Africa. It was actually following in the footsteps of two other species that had already made the journey.
Neanderthals (Homo neanderthalensis) left Africa some 300,000 years ago and spread through Europe and west Asia. Their close relatives the Denisovans are less well known – the first Denisovan bone was only found in 2008 – but may have spread widely across Asia.
Denisovans get their name from the location where the bones were discovered, Denisova cave in Siberia (named after an 18th-century hermit called Denis). Neanderthals are named after the Neander valley in Germany.
Number of years ago that Neanderthals probably died out. Modern humans and Neanderthals were probably interbreeding 50,000–60,000 years ago.
What were our relatives like? Their physical remains and artefacts provide some clues, mainly into Neanderthal life – only two teeth and a segment of Denisovan finger bone have been found. However, analysis of DNA from their bones is providing startling new insights into human evolution.
Inside the genome
The Neanderthal genome is very similar to the human genome – their DNA sequences differ by just 0.12 per cent. Some of the differences may provide clues about how Neanderthal biology differed from that of modern humans and how H. sapiens evolved after its split from the H. neanderthalensis lineage.
The sequence also sheds light on Neanderthal characteristics – the sequence of the MCR1 gene, for example, suggests they had red hair and pale skin. The Denisovan genome sequence suggests that they had dark skin, brown hair and brown eyes.
Notably, it appears that our ancestors did interbreed with both Neanderthals and Denisovans (and that Neanderthals and Denisovans also interbred). Some 1–4 per cent of the modern human genome is derived from Neanderthals – roughly equivalent to having a Neanderthal great-great-great-grandparent.
Modern humans and Neanderthals were probably interbreeding 50,000–60,000 years ago; Neanderthals probably died out around 40,000 years ago, possibly because they were unable to compete with H. sapiens (although a changing climate may also have played a part).
Not so dim after all?
Although they are commonly depicted as brutish, evidence is accumulating that Neanderthals may have been more sophisticated than previously thought. There is growing evidence of Neanderthal culture, including art and personal adornment, tool use, and systematic hunting of birds such as pigeons for food. It’s also possible that they may have had the capacity for speech.
A Denisovan genetic footprint
Denisovans are more closely related to Neanderthals than to H. sapiens. Even so, Denisovan DNA makes up 3–5 per cent of populations in east Asia, such as the Melanesians of the western Pacific and Papua New Guinea. Strikingly, a gene that enables Tibetans to survive in low-oxygen high-altitude environments seems to have been imported from Denisovans. There are also signs that the human immune system relies heavily on Denisovan and Neanderthal alleles.
Our lost relatives
Collectively, the findings indicate that the human family was once more diverse than it is now – no other Homo species now exist, and chimpanzees are our closest living relative. Once, however, multiple species existed, with a patchwork of humans living together and at times interbreeding. Although these species are long gone, their legacy lives on in our own genomes.Lead image:
Wellcome Library, London CC BY
- The other Neanderthal
- The complete genome sequence of a Neanderthal from the Altai Mountains (2014)
- A high-coverage genome sequence from an archaic Denisovan individual (2012)
- A rock engraving made by Neanderthals in Gibraltar (2014)
- Neandertals made the first specialized bone tools in Europe (2013)
- The earliest pigeon fanciers (2014)
- Micro-biomechanics of the Kebara 2 hyoid and its implications for speech in Neanderthals (2013)
- Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA (2014)
- The shaping of modern human immune systems by multiregional admixture with archaic humans (2011)