Would this be evolution?

[xdisciplex]

Imagine a child is born with some genetic mutation which makes the child be much more muscular (such myostatin abnormalities exist) and this muscularity turns out to be a huge advantage and this child has many kids and the kids also have this abnormality and they spread and spread and one day there will only be humans left which have this abnormality, would this be evolution?
Most will say no because there was no new information added but could sometimes less information not still be an advantage? If it's an advantage then why is it not evolution?
Or what would happen if a child was born with a third eye on his back? Would this be evolution or would they say that the information for eyes is not new and this means even a third eye does not equal evolution?

 

[UTEOTW]

Yes it would be because the frequency of the allele would be changing. In your case, it would go from non-existent to widely spread.

By the same token, since you have a new allele that previously did not exist, you have new "information."

Now the eye thing if a different story.