I think in some societies a baby starts by never being put down but always carried by their mother or someone very close to them for a considerable period before being passed on to get on with life one way or another when the mother has the next baby.
But in the life the child moves on to, in the group settings in other times or societies, a baby/toddler does not/did not go from mummy/father/carer to a busy nursery, but to a grandmother, aunt and older siblings, or cousins; and, outside that group, to a familiar entourage of people in a familiar place.
To my mind it is not that nurseries cause autism, but that even if they are good, some children are predisposed to be extremely stressed by the separation and by the atmosphere in the nursery, even though other children , more gregarious and confident, may take to it much better.
In addition, there does seem to be evidence of higher cortisol levels in young children in nurseries.
Might some children,
who are predisposed to stress in nursery settings but who seem all right before they go, have autistic dna so that nursery induced stress then becomes a possible environmental trigger - a bit like a traumatic experience might?
Re cortisol levels:
Excerpt from article linked below:
Interest in child care as a stressor capable of activating the HPA axis can be traced to a serendipitous finding published a decade ago (Tout, de Haan, Campbell, & Gunnar, 1998). Tout and colleagues were studying associations between day-to-day variability in cortisol levels and children's socioemotional behavior. When they examined their morning and afternoon cortisol data, they found that most of the children showed a rise in cortisol from morning to afternoon and they did so on most of the days they were in child care. This was remarkable as the typical basal pattern of cortisol production between mid-morning and mid-afternoon tends to be level or declining for children of this age (Watamura, Donzella, Kertes & Gunnar, 2004).
Since publication of the Tout et al. (1998)study, there have been a number of studies examining cortisol activity at child care. Two recent meta-analyses have summarized those findings (Geoffroy, Côté, Parent, & Séguin, 2006; Vermeer & van IJzendoorn, 2006). Both papers concluded that the rise in cortisol from morning to afternoon at child care has been convincingly documented and that this rise is not seen in the same children when they are at home on non-child care days. Both meta-analyses also concluded that age is a relevant factor, with larger increases being observed among the younger children (2- and 3-year-olds) as compared to the older children (4- and 5-year-olds). However, the two meta-analyses differed with regard to two critical issues: (1) whether child care quality influences the magnitude of the cortisol stress response over the day at child care, and (2) whether elevations in cortisol at child care are associated with children's temperament or behavior in the care setting.
Regarding quality of care, the first meta-analysis (Geoffroy et al., 2006) concluded that it has been shown conclusively that cortisol levels are higher and rise more over the day in poorer quality child care, whereas the second meta-analysis (Vermeer & van IJzendoorn, 2006) noted that nearly all of the child care studies of cortisol activity have been conducted in relatively high-quality care settings and thus child care quality cannot be the primary factor determining increases in cortisol at child care.
https://pmc.ncbi.nlm.nih.gov/articles/PMC2946618/
There a link between autism and high cortisol levels.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3245359/
Would these children be so easily stressed from birth, or might some environmental events make this innate proclivity much worse?