Scientists have long known that modern humans outside Africa inherit 2-3% of their DNA from Neanderthal ancestors. Now, two studies using ancient DNA have pinpointed a single period of interbreeding between 45,000 and 49,000 years ago as the source of this ancestry.
Neanderthals and early humans encountered each other multiple times over tens of thousands of years. However, not all interactions left a shared genetic imprint on non-African populations today. The key event that created this global genetic signature occurred between Neanderthals in Europe and newly arriving humans around 47,000 years ago.
This coincidence coincides with an estimated date for the out-of-Africa migration of modern humans, which was previously unknown. Researchers have identified a brief window of interbreeding that took place during this time period, providing new insights into human evolution.
Source: https://www.scientificamerican.com/article/when-did-neandertals-and-humans-interbreed-genomics-closes-in-on-a-date