Warning: potential butt-speaking ahead as this is not my subject. I have a suspicion that a lot of these things have a biochemistry that goes back a hell of a

Warning: potential butt-speaking ahead as this is not my subject. I have a suspicion that a lot of these things have a biochemistry that goes back a hell of a long way, and I think there's synthesis of various vitamin D's in fungi. Nearest I can find is https://en.wikipedia.org/wiki/Ergosterol https://en.wikipedia.org/wiki/Ergosterol "Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol found in cell membranes of fungi and protozoa, serving many of the same functions that cholesterol serves in animal cells. Because many fungi and protozoa cannot survive without ergosterol, the enzymes that synthesize it have become important targets for drug discovery. In human nutrition, ergosterol is a provitamin form of vitamin D2; exposure to ultraviolet (UV) light causes a chemical reaction that produces vitamin D2" So nothing to do with humans, and may go back to a common ancestor of fungi and protozoa. Note the particular arrangement of the four carbon rings https://en.wikipedia.org/wiki/File:Ergosterol_structure.svg https://en.wikipedia.org/wiki/File:Ergosterol_structure.svg I believe that's a steroid. You see the same thing in https://en.wikipedia.org/wiki/File:Testosteron.svg https://en.wikipedia.org/wiki/File:Testosteron.svg and much to my surprise the same thing appears in digitalis (the foxglove plant) https://en.wikipedia.org/wiki/File:Digitoxin_structure.svg https://en.wikipedia.org/wiki/File:Digitoxin_structure.svg Which suggests these chemical families go back a very long way indeed and most likely are radiate rather than parallel (edit: I mean convergent) evolution. Anyone who actually knows something about this, please correct or elaborate on anything.