Autism is caused by a bad sperm cell which is 1 in every 500 that enters the egg during conception that causes a mutation in the embryo which causes the embryo to partially divide into two but over time they merge back together. However, when this happens, the mother begins to experience paranormal activity that can be severe as demonic possession which cause the mother's body to undergo horrific mutations and perform all kinds of silly and pointless acts which trigger adverse effects on the growing fetus. In the last stage of pregnancy, the demonic possession ends but leaves behind a radioactive substance in the mother's womb that causes her to eat grasshoppers and fertilizer which has a 90% chance, along with the other factors, of causing the baby to develop autism within 1-2 years after birth.
Well, that's what I heard anyway.
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So simple, it's complicated