Fast, faster, failure

At the same time a selection probably occurs among the scabs. The most aggressive types killed their victims quickly – so fast that the scab could not first spread itself to new foxes. This type, consequently, died out. Slower-working scabs have a better chance to spread and to survive as well, as they do not immediately kill their victim.

Natural selection - again!

This is another example of natural selection. The scab adapts to its environment, where an important factor is how often foxes meet each other. This can explain why the fox is better able to survive scab now, and why the scab still remains.