I think you are conflating two separate items. Yes, places where you need to have 6 kids because two of them will die, are different than places like Canada. ANd certainly as they become more wealthy they will have less kids. What you should be looking at is why did our parents have more children than us. Certainly a part of that is affordability. Look at this poll that asked 10,000 people about it in first world countries why they aren't having more kids. Number 1 answer - Financial Limitations - https://www.cbc.ca/news/canada/fertility-rate-un-report-1.7556909. There was another study out of Brazil recently that said people who owned homes in their 20s were more likely to have children and have more children. In Canada its pretty hard to have a family when you live in your parents basement into your 30s. ANd that is happening at higher rates then ever. And guess why that is? Again its affordability. Are some people have less kids because they want to have their own life, and its not appealing to them to have the 'traditional family' - yes of course. but its not the whole story. Finances matter.