Random variation and natural selection are simple ideas in reference to genes, but memes don’t quite follow the same rules. Variation occurs, and new memes are born, but calling it random seems disingenuous. Selection also occurs, but calling it natural doesn’t quite fit. Memes can be consciously controlled, which makes them interesting things; unlike genes, they are capable of spreading and mutating amazingly quickly. The internet has made that spread and mutation even faster, to the point where an idea can make it all the way around the world faster than a human being.
Selective pressure, while different, is also much harsher on memes. Not only are boring ideas forgotten, but we can explicitly choose not to pass on ideas that we consider dangerous or wrong. This gives one meaning of the “double jeopardy” in the title. The other, fascinating meaning I was referring to is the interaction of selective pressure from genetics and memetics. The popularity of a particular meme can make a particular gene more or less useful, and vice versa.
This means that for a complete understanding, we cannot study genes and memes separately. Every genetic behavioural trait influences the memes we create and are willing to accept, and every meme we use affects the survival probabilities of our genes. They are tightly interwoven, and the selective pressures between them are therefore in a state of constant feedback.