Evolution is the process by which a species' genes or physical appearance changes gradually over time. By the early to mid-20th century, scientists realized that evolution can happen much more quickly than ever realized. Several factors can lead to rapid evolution. School of Earth and Atmospheric Sciences Assistant Professor James Stroud explains that "evolution is always occurring." Stroud and other researchers are using nonnative green iguanas as a case study for rapid evolution. The warm-adapted lizards are known to freeze and fall out of trees during Miami's infrequent cold snaps. 

"What we saw is that some die, but some survive — and the ones that survive can actually tolerate colder temperatures than the ones we measured before," Stroud says. "So it suggests that evolution might be happening."