Here's a question: how big should I be?

How organisms know how large to grow remains a mystery:

But here’s the thing. While we know quite a bit about the forces that cause animals to change size, we know rather little about how an animal’s body “knows” what size it is supposed to be. Let me show you what I mean.

Take a salamander. Let’s say it’s a certain size, and it has a certain number of cells. Suppose you double the size of the cells. Do you get a salamander that is twice as big? No. You get a salamander that’s the same size as it was before. But it has half the number of cells. Somehow, the salamander’s body can measure how big it is and stops growing when it gets to the right size.

(These animals look like regular salamanders, and are perfectly healthy. However, they are a bit stupid, apparently because they have half the number of brain cells. They’re less good than regular salamanders at solving mazes.)

And how about the diversity of life:

But the animal that really captivated me was the pygmy shrew. It was tiny! Smaller than my little finger. It weighs only a few grams (less than a quarter of an ounce), and is smaller than some insects. The Goliath beetle, for example, can weigh more than 100g (3.5 ounces), and can be as big as my palm.

I contemplated the pygmy shrew, imagining it burrowing through grasses, capturing small insects, perhaps engaging in an epic battle with an earthworm. I thought about its heart beating at 1,200 beats a minute, and about the fact that some species of shrew are so small that they can run on water.

And then I thought how remarkable: the shrew is a mammal, and the blue whale is a mammal. Yet the blue whale is the largest animal ever to have lived. The biggest ones — which, by the way, are females — can grow to be as long as 30 meters (about 100 feet) and can weigh over 120 metric tonnes (118 tons). One of the most massive blue whales ever put on the scales was 190 metric tonnes (187 tons).

Now for the next question: how do you put a blue whale on the scales???