I don't mean that the nursing period is so much a differentiating factor for the outcome, but rather that if the parents chose to breastfeed, that is one and about the only biologically differentiated role between a mother and a father, thus needs to be accounted for in some way. Ideally men should take more of other child caring burdens during the breastfeeding, but that depends on various other practical factors, so I wouldn't call men up for failing to do that.
“Linked” is a weasel word for lack of a a quantifiable result. (Not breastfeeding increases autism risk by X%.) The better thing is to look to the massive medical experiment we happened to have conducted in the last 50 years. From 1970 to today, breastfeeding rates have inverted. Back then, 70% of babies were never breastfed, even in the hospital. Today, it is the opposite.
But rates of autism are not much higher among Gen X-ers than millenials.
