by Feed your head with a play by Pamela Olson

Created on: March 03, 2009

A Billion Heartbeats
A billion heartbeats is the limit, but the human brain is the game-changer.

Have you ever thought how many heartbeats you have left before you die? In 2004, mathematician and theoretical physicist Geoffrey West arrived at the Santa Fe Institute (SFI). Dr. West soon begin to think about the beats of his heart. He knew everything dies; the question is how fast? He also knew the cells of a body are the room housing the mitochondria, the prodigious metabolic motor. The process by which carbohydrates are converted into energy is known as the Krebs Cycle. In 1837, physician

Hans Krebs, a later to be Nobel Prize winner, discovered that carbon dioxide rolls down the energy hill releasing energy and picking up carbon along the way. The result is that all species have the same conceptual blueprint.

Species have completely different life spans though. Tortoises and whales live more than two hundred years; a shrew lives about two years, a redwood tree a thousand years, and a fruit fly a month, a rhino fifty years, a gazelle twenty years. Why?

To answer this question Dr. West started with the 1930s work of Swiss-born chemist Max Kleiber. The Kleiber Ratio is that for every creature, the amount of energy burned per unit of weight is proportional to that animals mass raised to the three-quarters power. That means smaller takes more calories per pound to stay alive, while larger takes less calories per pound to stay alive. The pattern is of increasing efficiency.

The answer to the length of life turned out to be the faster the heartbeat, the shorter the life, the slower the heartbeat, the longer the life. The pattern discovered is that in general all amphibians, birds, fish, mammals and reptiles have roughly a billion beats per lifetime. Whales' heartbeats average 10-15 a minute, even slower while diving, shrews 850 beats a minute, even faster to 1,500 when frightened. Human's hearts beat at around 70 a minute. That means humans shouldn't be living past young adulthood. The reason humans are the sole exception to the rule is our big brains that have figured out how to bend the rules.

Dr. West discovered that Kleiber Ratio's is universal: "There's this exquisite interconnectivity. All the structures have different forms and functions, but all of them adhere to the same scaling pattern." Capillaries grow into veins and arteries according to the same three-quarter-power scale. So also do neural fibers by becoming whole nerves then becoming nerve bindles. From the

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