>> it's not close enough to say that it's the exact virus that gave rise to this one in a simple evolutionary step. but that kind of gap, 4%, means years, means decades in terms of natural evolutionary time. >> and that evolution means something. typically, after a virus makes the jump from animal to human, it sputters along, evolving, learning how to become more efficient. that takes time. with sars-cov 2, it came screaming out of the gates. >> normally, it takes a while for it to figure out how to become more and more efficient in human transmission. >> in the lab, do you think that process of becoming more efficient is happening? >> most of us in the lab, trying to grow a virus, we try to grow better and better.