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I've been wondering how much contraception introduces genetic selection against child abuse tendencies. My tentative belief is "a lot, and so a huge source of suffering is diminishing for future humans". Big if true.
My guess is that child abuse is disproportionately done by people who did not actively prefer to have the child (at all, or at a particular time in their life). Historically there was little selection for the trait of actively wanting children and being interested in their interiority. Now, because having children loads so much on whether it will feel fulfilling to the parent as an individual, and because the standards for the quality of the parent-child relationship are so high, there's probably a lot of selection for this.
(The heritability of fertility behavior is maybe 30%, and maybe more so with contraception.)
In the past, it wasn't about an indifference or unavailability of protection, but economic considerations that children could be put to work which may have lead to a deliberate decision to have larger families (which is not necessarily at odds for "wanting children"). Or as these researchers put it:
Children were very profitable assets since their pay was very low, were less likely to strike, and were easy to be manipulated...Children from poor families were expected to participate to the family income, and sometimes they worked in dangerous conditions in 12-hour shifts.
Radfar A, Asgharzadeh SAA, Quesada F, Filip I. Challenges and perspectives of child labor. Ind Psychiatry J. 2018 Jan-Jun;27(1):17-20. doi: 10.4103/ipj.ipj_105_14. PMID: 30416287; PMCID: PMC6198592.
The period of time, the 1800s, that Radfar et. al refer to was a time of early industrialization. And it appears that as an economy becomes more industrialized: child labor increases rather than decreases (and my assumption here is that with it "actively wanting children" increases, again for economic reasons):
We found that in early industrialization the number of children working, and the number working in factories both increased, while the age at which children started work decreased.
Sara Horrell, Jane Humphries,"The Exploitation of Little Children": Child Labor and the Family Economy in the Industrial Revolution". Explorations in Economic History, Volume 32, Issue 4, 1995,
Studies in Ethiopia in recent years suggests that the larger the household - the higher probability a child will be forced to work:
The result from the OLS estimation revealed that child labor exploitation which is measured by child labor hour
found to be significantly associated with age of the child, household size, monthly income of child’s parent, sex of the child, and educational level of child’s father and the parents of the child under debt.
ADMAW, TEREFE, and Surajit Ghosal. "Socio-economic determinants of child labor exploitation: the case study of Jimma Town, Ethiopia." Eureka 2581 (2018): 4249.
At the household level, resources such as (income, agricultural land, literacy of the head) and household size influence the child labor. Better income and literacy of the household head lower the likelihood of child to be engaged in child labor. With regard to community level factor availability of primary school reduces the likelihood of child to be engaged in child labor.
Abebe, G., & Fikre, S. (2021). Individual, household, and community level factors of child labor in rural Ethiopia. Cogent Social Sciences, 7(1). https://doi.org/10.1080/23311886.2021.1961402
The concept of demographic collapse in countries like Japan and Italy (see AP link below) in particular is well known at this point -- where an increase in longevity (whether that is due to better living standards or better medicine, or both) -- coupled with lowering fertility rates has caused "aging" populations. Ironically the situation is the reverse of the circumstances above:
Surveys show that younger Japanese are increasingly reluctant to marry or have children, discouraged by bleak job prospects, a cost of living that is rising at a faster pace than salaries and a corporate culture difficult for women and working mothers. - Associated Press
In industrialized countries children are no longer economically desirable, they become a liability, which presumably means the pool of people who are having children skews higher towards those who "want" children - even at great personal cost (Consider IVF which presumably is opted by people who are particularly determined to have children. It is not cheap, and even if it is subsidized can be quite a distressing experience).