The fecundity pleiotropy hypothesis you're referencing is studied in Ablaza et al.'s analysis on the Dutch data, with no support.
Looking at the biographies, it looked to me like these families were using their non-eldest sons to expand their influence and grease whatever wheels they might need, but someone who knows more about European history agreed with you and pointed out that this was also a way to ensure that in world of with primogeniture to maintain dynastic wealth, younger sons would have financial support from the church.
Thanks!
The fecundity pleiotropy hypothesis you're referencing is studied in Ablaza et al.'s analysis on the Dutch data, with no support.
Looking at the biographies, it looked to me like these families were using their non-eldest sons to expand their influence and grease whatever wheels they might need, but someone who knows more about European history agreed with you and pointed out that this was also a way to ensure that in world of with primogeniture to maintain dynastic wealth, younger sons would have financial support from the church.