The Sparseness Adaptation theory of autism shows that some autism is the result of adaptation to the sparseness of population frontiers. The theory is about how autism came to be. It points out that lack of social ability is the main feature of autism. The theory shows that autism is not always a disease and that some forms of autism exist for a simple reason: Every population has a surrounding frontier where there are few members. Adaptation to frontier sparseness produces a Sparseness Adaptation Syndrome that plausibly accounts for much of autism. In other words autism is an expected result of adaptation to the unrelenting sparseness of population frontiers. Because every population always has a surface, autism is a natural and major feature of brain evolution. The theory expects autism to have a range of severities and many varieties. These prevent tidy diagnosis of autism. The Sparseness Adaptation theory of autism does not strictly depend on Darwin's theory of evolution, and unlike Darwin's theory it makes predictions. For example, it predicts a correlation of autism and global position of ancestral homeland. The theory also explains why autism occurs more often in males than in females.

Read a brief tutorial on the theory, featuring an  Autism Evolution Simulator