A 2010 study in the journal Science provided the first DNA evidence that Neanderthals had long ago mated with ancestors of living people. A 2014 study suggests up to 50% of the original Neanderthal genome might be preserved, but spread into different sections across all humans living today. For people not of sub-Saharan ancestry, the most recent analyses suggest around 1% to 2.4% of their DNA originally came from Neanderthals. A 2020 study in Cell found tiny amounts of Neanderthal DNA in people from a sub-Saharan background, which they probably gained when humans from Eurasia migrated much later into Africa.
Neanderthal genes in living people seem to have come from one phase of mating around 55,000 to 60,000 years ago, yet we know from DNA in Homo sapiens fossils that mating was happening later too, around 40,000 to 45,000 years ago just before Neanderthals went extinct. Genetic data from much older Neanderthal fossils also tells us that far more ancient encounters also took place with Homo sapiens between 100,000 and 200,000 years ago, yet those periods of mating left no descendants alive today.
Scientists have compared the DNA of Neanderthals with that of modern humans to better understand how Neanderthal-derived genes shape traits in living humans. Some of the most strongly retained genes related to immunity, which makes sense as the resistance Neanderthals had built up to local Eurasian pathogens over 300,000 years would have been useful to H. sapiens people entering the continent for the first time. Additionally, a different genetic legacy from Neanderthals appears to promote fertility and be protective against miscarriage.
Yet other effects can be subtle. For example, a 2018 study in the journal Current Biology found that people with particular Neanderthal gene variants show some differences in brain shape, but not enough that you would notice when meeting them.
Some of what was perhaps historically useful may have negative impacts today. For instance, one Neanderthal genetic variant makes people today more sensitive to pain, which could lead to more rapid aging. A 2023 study found Neanderthal DNA strongly linked to “Viking’s Disease,” or Dupuytren’s contracture, while a 2014 study in Nature tied Neanderthal genes to lupus, Crohn’s disease and other autoimmune disorders.
And in 2020 researchers reported that one particular Neanderthal genetic variant makes people twice as likely to become severely ill from COVID-19; if they inherit two copies, the risk is even higher. However, the picture here is complex. In 2021, a study in PNAS showed a different Neanderthal gene offered protection against severe COVID-19.