Adaptation.

As temperatures dropped around south Florida, iguanas literally froze and fell out of trees. But they don't typically die, rather there's a hibernation like thing they do, and they remain alive.

A decade or so ago, many more iguanas were seen around when temperatures dropped than were seen this time.

What gives? The population actually increased, and the temps were certainly cold enough.

It's a little thing that we call adaptation. Over the last few decades, iguanas it would seem, have developed an ability to withstand the cold. This is in their genetics.

It's in ours too. Over a relatively small span of time, we can adapt. And start an evolutionary process.