The paper, Independent and dependent contributions of advanced maternal and paternal ages to autism risk by Shelton, Tancredi and Hertz-Picciotto released two weeks ago. It describes how older mothers are far more likely to have an autistic child.
Based on the first examination of heterogeneity in parental age effects, it appears that women’s risk for delivering a child who develops autism increases throughout their reproductive years whereas father’s age confers increased risk for autism when mothers are <30, but has little effect when mothers are past age 30. We also calculated that the recent trend towards delayed childbearing contributed approximately a 4.6% increase in autism diagnoses in California over the decade.
In 1998 I posted at sexualselection.org the hypothesis that older mothers will be discovered to be more likely to have autistic children because their testosterone levels are significantly higher. Simon Baron-Cohen conducted a number of studies that concluded that testosterone level in the mothers are directly connected to autistic tendencies. This study by Shelton, Tancredi and Hertz-Picciotto makes perfect sense in the context of mother’s testosterone levels impacting maturation rates, causing autism.