Land-ownership in Europe was inherited by eldest sons, which was understandable as it carried military obligations, to raise armies and fight on the side of the king or other superior when required to do so. Females inherited only when there was no male heir.
Marrying an heiress with estates of her own, which was often done (for example) by British aristocrats in the 19th century, was a way of enlarging the estates of the family into which she married. This raises the question: why did the heiress’s family have no male heirs – why was she the heir in the first place? Was there some anti-male factor in their genes? If a family continued to marry into such families, perhaps it was decreasing its ability to produce viable male offspring.
I recall reading in H.G. Wells’s Outline of History that the Habsburgs ‘married their way to world power’. This led ultimately to one of the largest empires of the Middle Ages but also to the prevalence of haemophilia in the royal families of Europe. Haemophilia is genetically determined, carried by females as a recessive gene but more or less rapidly fatal to males who inherit it.
A somewhat similar pattern seems to have been shown by my ancestors the Cleares (then spelt Clere), descendants of the Duke of Clere Monte, who came over with William the Conqueror. For a time they flourished and their coats-of-arms became ever more complicated as they added the insignia of heiresses. They had several manor houses in Tudor England.
Eventually, however, they had no male heir of their own, having produced female triplets. These, presumably, married into various aristocratic families, leaving the name of Cleare (or Clere) to be carried on by their father’s younger brothers and any other male relatives, without estates attached.
There are various indications that, even after losing their estates, people with the name of Cleare were IQ-ful and got into responsible positions. The only people with that name outside my mother’s family of whom I have become aware were a retired bank manager, and someone with a doctorate in chemistry who was on the Board of Directors of Johnson Matthey.
The effect of marrying heiresses on European dynasties is one of the many issues which could be developed by the History Department of my unrecognised independent university for which, once again, I appeal for funding to enable it to contribute to modern debates by drawing attention to suppressed points of view, instead of being stifled and suppressed as it is at present.