As I was kissing the sprogs goodnight last night:

Younger offspring: If we get boo-boos more than seven times, do we not heal any more?

Elder offspring: Huh?

Younger offspring: Well, if we have seven layers of skin*, once you get cut or scraped in the same place the seventh time, don't you use the last layer? After that, don't you run out of skin?

Dr. Free-Ride: Umm, I'm pretty sure that as you shed the outer layer, or scrape it or whatever, you're growing more layers underneath.

Younger offspring: But that would be more than seven layers, wouldn't it?

Dr. Free-Ride: I don't think it's that you have seven layers total over your lifetime. I think it's at a time.

Younger offspring: Oh. So new layers grow underneath?

Elder offspring: That's creepy!

Dr. Free-Ride: Why is that creepy?

Elder offspring: To have new skin growing secretly underneath the old skin? It's like a weird alien fungus growing!

Dr. Free-Ride: What would you rather have happen?

Younger offspring: Should layers of skin grow on the outside?

Dr. Free-Ride: If you ask me, that would be more like fungus. It would be pretty hard for the body to grow new skin that way.

Elder offspring: Well ...

Dr. Free-Ride: Or would you rather be like an onion, with all your layers already there?

Elder offspring: Maybe.

Dr. Free-Ride: Of course, if your skin was like the layers of an onion, instead of growing, each time you shed skin you'd get smaller and smaller.

Younger offspring: And you'd make me cry.

Dr. Free-Ride: Har!

Elder offspring: So what would happen if you got down to your last layer of skin?

Dr. Free-Ride: Your insides would be exposed to the sun and the wind, to air and water and dust.

Younger offspring: Ew!

Elder offspring: Why would air be a problem?

Dr. Free-Ride: Well, your cells have a lot of water in them. Without the barrier the skin provides, I bet that water would evaporate. Almost like leaving a glass of water on the counter for a few days.

Elder offspring: Why wouldn't it be like an aquarium? The top of our aquarium was exposed to the air.

Dr. Free-Ride: Yeah, and we had to keep adding water to it.

Younger offspring: With no skin, would we be all bones and muscles?

Elder offspring: And internal organs.

Dr. Free-Ride: And connective tissue, like tendons and ligaments. And cartilage.

Younger offspring: What's cartilage?

Dr. Free-Ride: You know, if you two were meat eaters who had some familiarity with chicken-on-the-bone as a food, you'd have an acquaintance with cartilage. But, seeing as how raising chickens for food apparently contributes more to carbon emissions than driving an SUV would, I'm OK with you not having first-hand experience with cartilage right now.

Younger offspring: Meat eaters cause global warming?

Dr. Free-Ride: Well, the practices involved in raising the animals as food contribute to global warming. Also, those animals burp and fart lots of methane, which is a serious greenhouse gas.

Elder offspring: But if they raise all those animals that way for meat eaters to eat, then meat eaters do cause global warming!

Younger offspring: Even John McCain?

Elder offspring: Especially John McCain!

Dr. Free-Ride: Look, I have no idea how much meat John McCain eats.

Younger offspring: Is Barack Obama also a meat eater?

Dr. Free-Ride: As far as I know, he is.

Younger offspring: Oh no!

Dr. Free-Ride: Look, this isn't the year we're going to put a vegetarian in the White House, but one of these years it will happen.

Younger offspring: I hope so.

______

*The younger Free-Ride offspring claims to have learned that humans have seven layers of skin while visiting an aquarium touch-tank with the Grandparents Who Lurk but Seldom Comment. The point of comparison was a sea creature (perhaps an anemone) that, when stung, sheds its outermost layer of skin.

My own view is that the precise number of layers humans have at a given time is less important than the fact that there are more than two of them simultaneously.