Final answer:
Early humans interbred with Neanderthals, leading to a mixture of Neanderthal and other genes in the modern human gene pool.
Step-by-step explanation:
According to DNA evidence from fossilized bones, it has been discovered that early humans interbred with Neanderthals and other archaic populations. This is supported by the finding that modern humans outside of Africa have about 2 to 3 percent similarity to Neanderthal DNA. Furthermore, genetic exchange between Neanderthals and modern humans likely occurred as modern humans migrated out of Africa, resulting in a mixture of Neanderthal and other genes in the modern human gene pool.