Watch "Outlander" Much?Caduceus said:This also worked the other way round. If the man was infertile, he would be more likely to adopt a child if his wife conceived with his own brother than with a genetically unknown man.
Given how potent the XY Chromosome is, and how resistant that it is to change, this would be optimal. Even though they had no idea how genetics officially worked back then, they had a clue. Yes a man is basically cuckolded, but being a biological uncle and legal father is better than nothing especially if you need male airs.
As related repeatedly in literature and scripture, raising someone that is not related to you causes a lot of issues that most people don't realize until it is too late. Just say no. Even in this age where IFV can use anyone's genetic material, these issues come up all the time.