Scattered across living people, about a fifth of the Neanderthal genome still survives
Most people carry only a few percent of Neanderthal DNA, yet different people carry different pieces. Pooled together, roughly 20 percent of the Neanderthal genome survives in modern humans, and one study of Indian genomes raised the prospect of reassembling it from the living.
Reading Neanderthal DNA became possible in the late 1990s. In 2006 the Max Planck Institute for Evolutionary Anthropology and the company 454 Life Sciences promised a full genome within two years; the mitochondrial sequence came in 2008 and the nuclear genome in 2010. Contamination dogged the work. Svante Pääbo's team discovered that 11 percent of one sample was actually modern human DNA, and labs now tag freshly extracted strands with short four-letter labels so ancient material can be told apart. The 2010 genome, drawn from bones in Croatia's Vindija Cave, also contained roughly one error per 200 letters. A far cleaner genome came in 2013 from a 50,000-year-old toe bone in Siberia's Denisova Cave.
Those genomes confirmed that our ancestors and Neanderthals had children together, more than once. Today's inherited segments trace to an encounter about 250,000 years ago, probably in Eurasia, and a later one, somewhere between 65,000 and 47,000 years back, around the Near East. Estimates for modern Europeans run around 1.8 to 2.4 percent and slightly higher for East Asians. A 2020 study even found 0.3 to 0.5 percent in five African populations, probably brought back by Eurasians migrating home. A survey of 2,762 Indian genomes identified 1,524 million base pairs of Neanderthal sequence in total, against a human genome of about 3,000 million.
The legacy is mixed. Neanderthals lived in tiny, inbred groups, perhaps only 3,000 to 12,000 breeding adults, so they accumulated mildly harmful mutations; early hybrids may have been up to 94 percent less fit than contemporary humans. Many such variants were slowly purged. Others stayed because they helped, especially immune genes: an estimated 25 percent of Europeans' Neanderthal inheritance and 32 percent of East Asians' may relate to fighting viruses.
One gap is telling. No living human carries Neanderthal mitochondrial DNA, which passes only from mothers, suggesting most crossbreeding paired Neanderthal fathers with modern human mothers.
Source: Neanderthal genetics
