All other species on this planet are gene machines only. They don't imitate at all well; we alone are gene machines and meme machines as well.

Imagine a world full of brains, and far more memes than can possibly find homes. Which memes are more likely to find a safe home and get passed on again?

I have not come up with anything original. It needs a better brain than mine! I have done what I can do in taking Dawkins' idea and extending it.

In proportion to our body mass, our brain is three times as large as that of our nearest relatives. This huge organ is dangerous and painful to give birth to, expensive to build and, in a resting human, uses about 20 per cent of the body's energy even though it is just 2 per cent of the body's weight. There must be some reason for all this evolutionary expense.

Just as the design of our bodies can be understood only in terms of natural selection, so the design of our minds can be understood only in terms of memetic selection.

Finally, we might decide that civilisation itself is worth preserving. In that case we have to work out what to save and which people would be needed in a drastically reduced population - weighing the value of scientists and musicians against that of politicians, for example...

The sale of sex in modern societies is not about spreading genes. Sex has been taken over by the memes.