When and why did adult adoption decline?

[Noncommunist]

Throughout much of the Roman period, adult adoption was fairly common and many families used it to carry on their name and ensure good heirs. So why and when did it decline? Given that it could ensure a clear succession to a competent heir, why would medieval and early modern Europe not use it to prevent succession crises that plagued many dynasties?

[SwordsMaster]

Divine Right to rule

[Myth]

Adoption in Rome was in the form of patronage from an old, wealthy man to a young upcoming youth. When that youth advanced in office and power, he would in turn repay his benefactor.

The late Republic and the Empire deviated heavily from the old Roman ways of honour, earning office through valour and military commmand and so on. The fall of Rome and all the violent rebelions can be partially attributed to the corrupt and inept power hierarchy in the late empire.

Obviously in feudal Europe this was not the way to do it. Bloodlines were important, as the nobility set themselves apart from the yeomanry and common folk not just by material wealth but also by blood.

[Kralizec]

Adoption in Rome was in the form of patronage from an old, wealthy man to a young upcoming youth. When that youth advanced in office and power, he would in turn repay his benefactor.

That's accurate enough, but in the early empire at least it was customary for the reigning emperor to adopt someone so that he would succeed him. Which is what the OP meant, I gather.

I have no idea why the tradition didn't persist. It could have something to do with the fact that most European kingdoms (France, Germany and England at least) followed the Sallic law of succession, which originated with the Franks. Which makes me wonder if the Byzantines practiced adoption for the sake of succession.

[Noncommunist]

That's accurate enough, but in the early empire at least it was customary for the reigning emperor to adopt someone so that he would succeed him. Which is what the OP meant, I gather.

I have no idea why the tradition didn't persist. It could have something to do with the fact that most European kingdoms (France, Germany and England at least) followed the Sallic law of succession, which originated with the Franks. Which makes me wonder if the Byzantines practiced adoption for the sake of succession.

I can't think of any Byzantine Emperors that did that though it probably would have helped given some of the emperors that arose.

[Seamus Fermanagh]

There is an interesting paper to research and publish here.

My guess, off the top of my head, is that the answer is the decrease in child mortality.

Romans and others adopted to get heirs/continue the gens. Why would you adopt someone had hadn't already survived to age 12+ and thereby be sure that most of the child-deaths were no longer a risk?

As infant mortality dropped way off with modern medicines and public health efforts, you could afford to "invest" in a young child with reasonable expectation of a return on that investment -- plus you could raise them fully as your own in terms of language, culture, family traditions and the like.

Done young enough and with enough basic physical similarity, and you need never let ANYONE know that they were not your biological children. Thus you could protect yourself from the social sin of being barren (which was a bit of a "sin" for much of human history).

Again, that's off the top of the head...