by Robert Krulwich
We wax, we wane. It’s the dance of life.
Every living thing is a pulse. We quicken, then we fade. There is a deep beauty in this, but deeper down, inside every plant, every leaf, inside every living thing (us included) sits a secret.
Below the pulse, which you see here, elegantly captured by Shanghai photographer/designer Yunfan Tan, is a life/death cycle, a pattern that shows up in the teeniest of plants, (phytoplankton, algae, moss), also in the bigger plants, (shrubs, bushes, little trees) — and even in the biggest, the needle bearing giant sequoias.
Everything alive will eventually die, we know that, but now we can read the pattern and see death coming. We have recently learned its logic, which “You can put into mathematics,” says physicist Geoffrey West. It shows up with “extraordinary regularity,” not just in plants, but in all animals, from slugs to giraffes. Death, it seems, is intimately related to size.
Life is short for small creatures, longer in big ones. So algae die sooner than oak trees; elephants live longer than mayflies, but you know that. Here’s the surprise: There is a mathematical formula which says if you tell me how big something is, I can tell you — with some variation, but not a lot — how long it will live. This doesn’t apply to individuals, only to groups, to species. The formula is a simple quarter-power exercise: You take the mass of a plant or an animal, and its metabolic rate is equal to its mass taken to the three-fourths power. I’ll explain how this works down below, but the point is, this rule seems to govern all life.
A 2007 paper checked 700 different kinds of plants, and almost every time they applied the formula, it correctly predicted lifespan. “This is universal. It cuts across the design of organisms,” West says. “It applies to me, all mammals, and the trees sitting out there, even though we’re completely different designs.”
It’s hard to believe that creatures as different as jellyfish and cheetahs, daisies and bats, are governed by the same mathematical logic, but size seems to predict lifespan. The formula seems to be nature’s way to preserve larger creatures who need time to grow and prosper, and it not only operates in all living things, but even in the cells of living things. It tells animals for example, that there’s a universal limit to life, that though they come in different sizes, they have roughly a billion and a half heart beats; elephant hearts beat slowly, hummingbird hearts beat fast, but when your count is up, you are over. Plants pulse as well, moving nourishment through their veins. They obey the same commands of scale, and when the formula says “you’re done,” amazingly, the buttercup and the redwood tree obey. Why a specific mathematical formula should govern all of us, I don’t completely understand, but when the math says, “it’s time,” off we go …