If we were to use Wolves and Chihuahuas as an analogy for a virus. A wolf is the baseline and a Chihuahua is the variant. How do they know it's different? Is there a laboratory isolated difference in genetic structure, shape, and size? Or is it all just based solely on cataloging symptoms? Such as how bite marks and fatality would differ from each other. I have seen no explanation on what makes the delta variant definable in contrast to the original virus.