Regarding the unique physiology of the hagfish, a reader writes:
Four hearts sounds better than one. If the one you have fails, you’re dead, unlike say if one kidney, or one lung or one eyeball fails. Redundancy is good. There’s clearly no intelligent design when one discovers what a pile of kludges the human body is.
I’m not sure I agree that four hearts are going to be better than one – there will certainly be a resource cost, as well as possible problems with vascular coordination. I assume they have four hearts due to their environment (what else?!), which is 250m.
