Relation to slowed physical development

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My understanding, mostly from a psychiatrist, is that as humans developed larger brains they needed more time to "load the software", so they grow up in 20 years instead of 2 years like horses. Sexual ability is not of much use during the extra years, so sexual development is suspended. I don't have references in hand for this, but I encourage others who are aware of such to add them. Perhaps there is an article that could be linked. I read an article in National Geographic that said that more rapid development was one of the reasons that Neanderthal Man did not survive an ice age.