So I missed this book, it was published in 2014, but having read it now, I thought I'd still share it. While on assignment for Outside Magazine, James Nestor covered a free diving competition in Greece. While Nestor is amazed by this ability to hold ones breath for more than three minutes, and dive to more than 300 feet, he becomes disgusted as the divers emerge sometimes unconscious, at times with blood pouring from their noses. At those depths the lungs can "shrink to the size of two baseballs." However it's the competition that he dislikes, the constant and reckless need to beat the other guy's record, to go ever deeper. Outside of competition, freediving can be a practical and beautiful exploration of what lies below. Nestor writes freediving "is the most direct and intimate way to connect with the ocean." He learns to freedive himself, and learns about "The Master Switch".

Why I was so drawn into this book is the way Nestor writes about science in a way that is easy to understand, without dumbing down to his readers. While reading his description of the Master Switch of Life, I was amazed that the human body has this mechanism, and I understood it. The human body can withstand the pressures of the ocean because it reflexively retreats blood from its extremities to the vital organs. This keeps the brain flooded with oxygen and the lungs full of enough blood to keep them from collapsing. There have been studies that this reaction only happens under water; the same amount of pressure on land will not elicit this response. It's this and innumerable other discoveries about us and our connection with the water and the animals that inhabit it that kept me so enthralled.

Nestor takes us on a road trip around the world, following self taught and "real" scientists. We follow Nestor to Honduras, to a man with a homemade submarine. We're in Honduras because there is virtually no law against taking tourists down 2,500 feet in a creaky homemade sub. It is a terrifying and amazing dip into the "midnight zone", where there is no light. At this depth some animals use bioluminescence, which can be seen only when the sub's lights are off.

Another interesting connection Nestor makes between humans and marine life is the ability to use echolocation. Blind humans use the similar echolocation clicking that dolphins and whales use to get around. Also he posits that humans have a magnetic navigational instinct similar to that of sharks and other animals.

One of my favorite parts of this book is when Nestor swims with sperm whales. Freediving with the mother whale, the "size of a school bus" and its "short bus" sized baby is exhilarating, and nerve wracking. Nestor has been taught to stay still in the water to allow the whales to come to him. There is absolutely no way to chase a whale while diving. The animals use their echolocation clicks to look him over, and with their clicks they also are able to x-ray, actually see into whatever animal their clicking at, to check out their organs. The water vibrates around Nestor. Once the whales decide that Nestor is ok, they change their clicking to "coda". This different clicking is thought to be personal, a way for whales to identify themselves. Perhaps they're introducing themselves. Nestor spends a lot of time with people trying to break the codes of whales and dolphins; trying to interpret their languages.

So from covering a couple of freediving competitions, this book emerges. Seventy one percent of the earth is covered in water. We know more about the moon, or Mars than we do about the ocean and its inhabitants. Toward the end of Deep we travel to the hadal zone, the deepest parts of the sea. Here there is still a vast amount of biodiversity, most of it still unknown. This book scratches the surface, and through facing his initial fear of freediving, Nestor pulls us all down to experience some of his wonderful and often times weird findings.