The problem was not caused by natural evolution though. The problem has been caused by man meddling with nature.
Now we have a problem that seems to be causing the death of our native Red Squirrel. Once extinct in this country I would doubt if like the Sea Eagle for instance ,if we could reintroduce in the future because the Grey Squirrel will still be around.
My guess would be that if the reds can get some sort of immunity resistance built in we should then concentrate on firstly keeping greys at bay in the red strongholds. Then if we can get some good breeding seasons so the native reds can increase we should be culling out greys in suitable habitat for reds. The scientists I believe have been working on a contraceptive for greys. Maybe science can help a bit more.
I also read that with the increase in Pine Marten in some areas they are having an effect on greys as they are easy to catch compared with reds
That would then be nature at work for evolution.
I would like to take heart though that at least people are talking about the subject openly. We may none of us be right but I for one am firmly on the side of our native red & if they appear here where they have never been then they will be culled.