Though I don't have a source to back this up, I really think that population densities were too low during those times for much Cro-Magnon-Neanderthal (funny ho

Though I don't have a source to back this up, I really think that population densities were too low during those times for much Cro-Magnon-Neanderthal (funny how one's capitalized and the other isn't) interaction. That said, aggression would not have been enough for humans, especially since the Cro-Magnons were probably weaker physically. There is always the possibility that there were changes in the environment that they couldn't cope with but our ancestors did. Longer childhoods could have been a hindrance. As you know, a larger brain does not necessarily mean a higher intelligence. It could have evolved to simply create a higher volume-surface area ratio that helped preserve heat in their heads.