Final answer:
Neanderthals and humans evolved from the same ancestral species, H. heidelbergensis, and there is DNA evidence of interbreeding between early humans and Neanderthals, with modern non-African humans having 1 to 4 percent Neanderthal DNA.
Step-by-step explanation:
We believe that Neanderthals and humans both evolved from the same ancestral species. Extensive genetic research has shown that both Neanderthals and modern humans (Homo sapiens) shared a common ancestor, H. heidelbergensis.
This ancestor lived around 700,000 years ago, eventually diverging into different hominin lines, with Neanderthals and Denisovans sharing a more recent common ancestor with each other than either did with modern humans.
The interbreeding between early humans and Neanderthals is documented through DNA evidence indicating that modern humans outside Africa carry about 1 to 4 percent Neanderthal DNA. This suggests that after early humans emerged from Africa, they interbred with Neanderthals as they spread across different parts of the globe.
Furthermore, a significant finding from DNA evidence is the discovery of a girl born to a Denisovan father and a Neanderthal mother, attesting to the interactions between these different ancient hominin species.
These findings underline the complexity of human evolution and the extent of interaction between various hominin species. Such interactions and genetic exchange highlight a dynamic history, which has ultimately shaped the genome of contemporary human populations.