Unexpected advances in physics lead to super-exponential increases in computing power (such as were expected from quantum computing), allowing brute-force algorithms or a simulated ecosystem to achieve super-intelligence.

Real-time implanted or worn sensors plus genomics, physiology simulation, and massive on-line collaboration enables people to identify the self-improvement techniques that are useful to them.

Someone uses ancient DNA to make a Neanderthal, and it turns out they died out because their superhuman intelligence was too metabolically expensive.

Reading all of LessWrong in a single sitting.