It was Hadrian who nominated Aurelius as his successor. Trajan chose Hadrian on his deathbed (although some of the ancient sources think it was actually Trajan's wife).
Interestingly enough, Nerva, Trajan, and Hadrian all tilted homosexual, and all of them seemed to choose their successor based on that memetic principle you mentioned.
You're right, I have remembered my events wrong.
The main point I wanted to make was that Trajan was the most impressive of the lot, and that he was found and elevated by meritocracy, not aristocracy.