Financial markets are dynamic. Prices vary every day, often without discernable news, and markets sometimes seem to have a mind of their own. The speaker presents a simple model in which agents compete with each other using simple rules, and are selected based on their profits and losses. This selection mechanism is culturally plausible, and is mathematically analogous to models for reinforcement learning in the brain. The price varies all the time, even without any input of information.
Speculators learn but never entirely eliminate patterns in prices.
In some cases they reduce market volatility, but in other cases they make it worse. There is a mathematical similarity to predator-prey models in biology, that makes clear the sense in which it is accurate to think of a financial market as an evolving ecology of trading strategies.