Fisher argued that fitness depended on variation, but this led to a paradox: After all, the more natural selection weeded, the less variation was left. This meant that the mutation rate had to be higher than he allowed for. But since most mutations were harmful, if their rate was too high the fitness of the population would drop. On the other hand, if natural selection scrutinized too harshly, the population could be wiped out entirely.
Confusing
