Experiments with rodents indicate that severe early psychological and social deprivation has lasting detrimental effects on learning ability that are not remedied by exposure to enriching experiences in adulthood. Findings indicate that environmental adversity early in life works to limit the development of intelligence with consequences for later functioning. Animal experiments are best viewed as supplying a rationale for early intervention in disadvantaged infants and children who would otherwise be likely to evince low intellectual capabilities later in life. Animal experiments conducted to date do not support an interpretation that early enrichment necessarily boosts later intellectual performance beyond the normal or species-typical range. They indicate that early intervention promotes normative development by preventing adverse early rearing conditions from leading to negative consequences for cognitive ability and self-regulation. The Abecedarian Project, an early enrichment intervention with infants from economically deprived backgrounds, is presented as an example of how early experience matters in terms of human intellectual development in disadvantaged populations. The results of that program reflect what one would expect from the rodent studies mentioned above.