One thing clearly at work here was the role of Severn's father -- he took her fishing and hiking regularly, and showed her his love and curiosity for nature. And he modeled the translation of that love of nature into action, with his work as the host of environmental TV shows and regularly speaking out on environmental issues.
My own dad was no internationally-known TV host, but he (and my mom) did much the same thing. There's a picture from before I can remember of me, fascinated by a mouse Dad brought home from his lab. Later, he'd take me in to feed crickets to his frogs. We went fishing, hiking, camping, scrambling over rocks, looking under logs, and bringing bugs home as pets. My parents made sure we saved our recycling (even though, in the late 70's, we had to drive to a collection spot to drop it off), and they canvassed for green politicians. They haven't stopped, and neither have my brother and I.
Thanks, Dad. Happy Father's Day!