It's very common to think that the reds and greys are close related.
As you can see, from this genetical species tree, they are actually 6 species apart.
That's like comparing a dog to a wolf.
As you can see,
all these squirrel species originated from just two main species.
The Prarie dogs and the chipmunks.
The Eurasien Red Squirrel has gone through 4 stages of evolution
before getting to the squirrel they are today.
The American Grey Squirrel have gone through 6 stages of evolution.
You could say that the grey are more evolved,
more adapt to the environment and the influence of humanity on nature.
While the reds are more "pure" in their species,
more fragile and not very good at adapting to any type of change.
The Greys are about 25% bigger, 50x stronger and
has a much better immune system than the reds.
Making a psychical fight between them a quick and sure victory for the grey.
It's like having a tiger fight a cheetah.
As mentioned, they also have a much better immune system,
able to withstand lots of foods and drinks, without getting sick or killed.
The reds are so much more sensitive.
Everyday chemicals, perfumes,
soaps, hair products, and detergents that we use without a thought,
could kill a red squirrel within hours.
A single bite of toast,
could make them incredibly sick and even get killed from it,
due to dehydration of diarrhea and stomach cramps.
You could even call them hypoallergenic.
So if you think about adopting a red,
you'd have better luck navigating a rhino through a porcelain shop.
This is why the greys are taking over the UK, from UK's native red squirrels.
Not only are they stronger, more capable than the reds,
they are simply put, evolutionary superior to the reds.
They can also carry the squirrel pox, that doesn't effect them much.
But to a reds, oh the reds, it's a sure, slow and extremely painful death.
I do not agree with the methods in which UK are handling this situation.
There are far better ways to solve this, than to hunt and kill grey squirrels.
The greys are 95% immune to this squirrel pox,
so my suggestion is to study road kills are make a vaccine for the reds.