When is selective breeding okay and when is it not? Provide evidence.

Farmers have been using selective breeding for improving their crop qualities and producing animals with better characteristics.

improved so that mankind can benefit from it.

Selective breeding is not okay on a bigger level where it might eradicate the natural varieties of plants and animals completely.  When done on a larger level, the wild-type traits of plants and animals will change and be removed completely. This will lead to lesser genetic diversity.