Human: The World Within

Through the eyes of a boxer, a first responder and a man with a bionic hand, see how the brain and its vast nervous system turn information into action.

The heart powers us through extreme physical and emotional challenges, from an ice climber's dangerous ascent to a widow’s grief and resilience.

Home to a sophisticated ecosystem, the human gut processes the fuel our bodies need to thrive — whether we're fasting or running an ultramarathon.

It's complex, invisible and always changing. Explore how our immune system fends off microscopic threats with extreme precision and speed.

A figure-skating duo masters jumps, a perfumer evokes memories, and a singer who is deaf learns pitch through the power and flexibility of the senses.

Unpack the science of hormones, infertility, epigenetics and more as expectant parents navigate the challenges and wonders of pregnancy and birth.