text: Intellingence is thought to be influenced by many factors, genetics being but one of them.\n\nObviously, injury or disease can damage the brain, and result in lower intelligence, as can other factors such as malnutrition.\n\nAlso important are the conditions encountered during early childhood development.  The brain has certain "critical windows", when it is most open for developing language, reasoning, spatial relationships, and other skills.  Children who do not receive the proper stimulus during these windows find it difficult, if not impossible to learn the skills in later life.