This is my post for day 26 of the Inkhaven writing retreat.

Okay, so you might just know the answer to this one. If so, I think it could still be fun to imagine you don’t, and play along.

I was once chatting with a friend who knew a lot about biology. I don’t remember what we were talking about, but perhaps it was things like endocrine glands, which are just little organ blobs who are responsible for making hormones.

And I remember wondering out loud to her, “oh, yeah, …and where is blood made? Presumably there’s just some organ whose job it is to make blood? I feel like I would have heard of it…” and she responded, “Oh, you didn’t know? Blood is made in the bones.”

And then my brain exploded with incredulity and objections (and also fascination and wonder, because I immediately believed her).¹ I was like, WHAT? Made in the WHERE? Why???

• It’s crazy that the main structural component of your body would be doing something else. It’s like if the steel beams of a building just so happened to also make good solar panels. Like, no, evolution, what are you doing. Separate things should do separate things. Bones do a great job holding me up. Their existence is justified.
• Where does the blood come out?? It’s not like there are little holes at the end of the bones where the blood vessels are attached? Like… does it come out the sides, or the ends, or …???
• Bones are all totally different shapes! And there are so many bones. Do your hips make blood? Your vertebrae? Your tiny foot bones? Your skull? Your teeth? Your ear bones??? This is just ridiculous.
• What happens when you break a bone??? That seems like a big problem. I mean I guess it’s not necessarily a bigger problem than if your blood was made in a single squishy blog inside your chest. But it still seems like a problem. If you break a bone real bad, does it just start… leaking blood? (In addition to the, erm, other blood you’d be losing.)
• If you lose a limb, I guess you just make less blood? Which seems… fine I guess? Especially since you have one less limb that needs blood. But still weird.
• Birds have super thin tiny bones. Do they just have less blood?
• Oh, but maybe bone-making bloods are a mammal thing? I mean that would be wild, but this whole situation is wild. Biology is lawless.
• Wait, there are tons of animals that don’t have any bones! Worms? Slugs? Insects have exoskeletons… next are you going to tell me that insect shells make blood? What about an octopus?

I think my friend must have put on a big grin and thought “this is going to be a fun time“. Because, it is true that blood is made in the bones, so all of these questions have answers. Some of them she knew, and some of them we had to look up. And exploring the world together is one of the best activity to do with someone like me.

1. And also, somewhere in the back of my mind, there was a little note of familiarity, of recognition. It went “oh, that feels familiar… something about bone marrow?” The skill of noticing that little feeling is part of what it means to be a rationalist, to be trying as hard you can to see the world as it is. ↩︎