You Read it up in the title NOW ANSWER!!!! Just Kidding.
Homo Neanderthalensis doesn't go extinct, having (somehow) spread to the Americas.
Spaiens and Neanderthals become the two human species on the planet. Between them, there is a percentage that can interbreed (not all, but some) they create a hybrid that eventually displaces both species. This new group, having better musculature, improved indurence, and a highly evolved brain (arguably more so than we are today) would have likely been experimenting with the Human Genome for at least 100 years by this time. The first and most important genetic augmentations becoming the re-introduction of an prehensile tail (that is as long as the spine), increased metabolic rates, increased muscle density, improved regeneration, introduction of photosynthetic organoids (or even other potential sources of energy which can then be used by the Mitochondrian), and some minor cosmetic features (things like Gray Eyes, Blue hair, etc.)