In this model, our brains relate to ideas the way life forms relate to genes. A brain can hold an idea just like a life form holds a gene. And brains act as vehicles for ideas the same way that we act as vehicles for our genes. But a fit idea isn't necessarily the most accurate. To survive, an idea just needs to find a place to lodge in the brain of a host.
Fit ideas can make lots of copies of themselves.
In this way they are just like selfish genes. The fit ideas must also be good enough to jump from brain to brain. So the more fit ideas are those that get copied and pass from one brain to the next. But fit ideas must also be fit enough to lodge in the nooks and crannies of lots of brains. This fitness for all kinds of brains is the most important factor in their survival.