Why do big creatures live longer? | Geoffrey West | Big Think

Why do big creatures live longer?
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Scientists have observed that in nature, all things scale with size in a way that is mathematically predictable.

Similar scaling laws hold for things like growth and lifespan. As theoretical physicist Geoffrey West explains, larger mammals generally live longer because of the inverse relationship between body size and the rate at which cells are damaged.

By having this theory of scaling laws, “you can determine what the parameters are, the knobs that you could conceivably turn to change that lifespan,” says West. Instead of living to be 100 years old, humans could someday hack our cells to last for two centuries.
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GEOFFREY WEST:

Geoffrey West is a theoretical physicist whose primary interests have been in fundamental questions in physics and biology. West is a Senior Fellow at Los Alamos National Laboratory and a distinguished professor at the Sante Fe Institute, where he served as the president from 2005-2009. In 2006 he was named to Time’s list of “The 100 Most Influential People in the World.”

Geoffrey West is the author of “Scale: The Universal Laws of Life, Growth, and Death in Organisms, Cities, and Companies”, find it at https://amzn.to/2UpdHi4
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TRANSCRIPT:

GEOFFREY WEST: All things scale in a very predictable way and they scale in a way that's non-linear. We developed this very elegant theory that what these scaling laws are reflecting are in fact the generic universal mathematical and physical properties of the multiple networks that make an organism viable and allow it to develop and grow. I think it's one of the more remarkable properties of life actually. Just taking mammals, the largest mammals, the whale, in terms of measurable quantities, is actually a scaled up version of the smallest mammal, which is actually the shrew. They are scaled versions of one another. If you have this theory of scaling laws, you can determine what the parameters are, the knobs that you could conceivably turn to change that lifespan. So it's a fantastic effect, it's a huge effect.

If you have this theory of networks underlying these scaling laws, manifesting themselves as scaling laws, you first ask, you know, is there a scaling law for lifespan? Every time you double the size of an organism, you would expect to double the amount of metabolic energy you need to keep that organism alive. Quite the contrary, you don't need twice as much metabolic energy. Systematically you only need roughly speaking 75% as much. So there's this kind of systematic 25% savings. Metabolic rate simply means how much energy or how much food does an animal need to eat each day in order to stay alive. Everybody's familiar with that as sort of roughly 2000 food calories a day for a human being. So here's this extraordinary complex process, yet it scales in a very simple way. Life span also increases following these quarter power scaling laws.

The scaling of these quantities is determined by the constraints of flows in networks. Those flows, they are dissipative, which simply means they involve wear and tear. Just as there's a lot of traffic going back and forth on the roads, and those roads wear out, they have to be repaired. And so it is, the traffic through our multiple network systems produce damage. The reason a large animal lives longer than a small one is because the metabolic rate per unit mass or per cell, gets systematically smaller, the bigger the animal corresponding to these quarter power scaling laws. So less damage is done at the cellular level the bigger the animal. When a given fraction of unrepaired damages occur, the system will become non-viable, that is it can no longer be sustained. That gives you a calculation of maximum lifespan. If you were to do the best you possibly could, this is as long as you could possibly live for a given size of mammal. And if you do that, you can understand where roughly speaking this hundred years for a human being comes from. More importantly, what could you do to make that go from a hundred to 200, for example? And there's two pieces of that, one is you could decrease, of course, the wear and tear or you could increase the repair. If you think about the damage that is occurring from metabolism, one way we could decrease damage is decrease the amount of food we take in. It may not be so pleasant in terms of your lifestyle but this would predict that you live longer. There have been some controversial experiments on monkeys...

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