"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."

That's fascinating that a heart can beat a billion and a half times. (And plants pulse too!)

Does that mean if we come up with a way to replace a heart it's kind of like replacing the transmission of a car?

Or would that be unnatural?

That's a good question, and I don't know the answer. Even if it were like replacing the transmission of a car, there's a whole lot of other parts that sustain wear and tear and over time that would probably need to be replaced, too. 

So until we can regenerate a lot of our parts, nature will continue to take its toll.

If you're lucky, you get to use all 1.5 billion heartbeats.

If you're lucky.