They became heavier and more streamlined, with dense bones that help them dive ... water with precision and grace.

As I plunge at last into the icy ... water, we’re wearing and carrying 200 pounds each. It feels like we’re learning to dive all over again. Moving is a struggle, swimming almost impossible ...

These free flow events are more likely when diving in cold water as regulators can freeze more easily. When a diver inhales, the regulator reduces high-pressure air from the tank to ambient pressure.

Penguins first evolved the ability to dive, like a puffin ... Those may no longer be needed as penguins forage in cold, salty water and typically swallow prey including fish, shrimp and squid ...