Answer:
Neandertals are closest relative to modern humans as their large brains size had to do with their meat diets. There were many theories including the Allens theory or Bergman theory their larger nasal apertures to cold environments.
Smaller bodies are adapted to more hot climates, and larger bodies are adapted to more cold climates as per Bergman's rule. Allen's rule says that the principle that limbs are longer in hot environments and shorter in cold environments.