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 isolation,shape, and size? Or is it all just based 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.