Complex sentence: Another reason is to create a dog with greater genetic variety, and although this is not a guarantee of better health, the scientific studies that have been done in this area have shown that crossbreds are both healthier and live longer than purebred dogs.
Split into simpler sentences: Another reason is to create a dog with greater genetic variety, although this is not a guarantee of better health. However, the scientific studies that have been done in this area have shown that crossbreds are both healthier and live longer than purebred dogs.