A spoken-and-transcribed guest-post courtesy of Partner, who caught upwards of seven hermit crabs today:
Hermit Crab Homes
Hermit crabs grow, but their shells don’t, because hermit crabs don’t grow their shells but find them. When a hermit crab grows too big for a shell, it will find a bigger one. If the bigger one is too big for that hermit crab, it will just hang out near the shell, in the hope that some other hermit crab will come take that bigger shell and leave behind its shell. Because of this, you can get a whole line of hermit crabs: several smaller hermit crabs are waiting to size up their shell. As soon as a bigger hermit crab comes and takes that too-big shell, it will free up a slightly smaller shell, and then another hermit crab could take that slightly smaller shell, etc., trickling down.
It’s like the kidney donation chain.
The Kidney Donation Chain
If I wanted to give you my kidney, but you and I are not a match, we’d be out of luck unless there were two other people, one of whom wanted to donate and the other to receive, and we were a reciprocal match so could swap. But generally, there are so many factors required for a kidney to fit that a direct swap is improbable. And they only let something like two or three people form a loop because they want to operate all at once. They’re afraid that, if they do them sequentially, the buddy of the first person to get a kidney will renege on his donation at the end of the loop because his incentive to give is gone.
Because of this structure, someone donating the kidney without needing a kidney for a friend or family member can change that loop from a loop into a line, which is really mathematically beneficial. And the altruistic donor is just giving away the kidney, no one’s on the hook for getting a kidney back to them, so there’s no risk of someone chickening out. If you choose to donate your kidney, you can kick off a chain that doesn’t just help the one person you are donating your kidney to, but can actually help all the people who exist in that chain, which can be a dozen people or more.
BBC Earth video on hermit crab shell swaps:
https://www.youtube.com/watch?v=f1dnocPQXDQ
Info on starting a kidney donation chain, including a way to get 5 loved ones to the top of the donation line if they ever need a kidney but you already gave yours away: https://www.kidneyregistry.com/for-donors/start-a-chain/