Its different when your grandparents are in their late 30's, early 40's. Modern reproductive ages are much, much later than they have been both historically and

Its different when your grandparents are in their late 30's, early 40's. Modern reproductive ages are much, much later than they have been both historically and prehistorically. Grandparents 600-4k years ago would have been in their late thirties, mid forties for all but a very few. Still unlikely to generate significant selection pressure considering that the vast majority of cancers are late in life. https://www.ncbi.nlm.nih.gov/books/NBK97292/ https://www.ncbi.nlm.nih.gov/books/NBK97292/