While the Australian study of almost 7,000 female twins found that parents had a moderate effect on the pregnancy of teens born between 1964 and 1971, parents had zero effect on the pregnancy of teens born between 1893 and 1964. A study of about 2,000 female Swedish twins born in the Fifties also found zero effect of upbringing on teen pregnancy.
If these countries are like the US there’s massive changes in marriage rates of teens. The thing we probably actually care about is out of wedlock or accidental pregnancy and thats a moving variable that id also expect to outweigh parenting effects. Pre-1950 the rate is flat meaning theres no parenting or cultural experience.
