[Arizhel]

Did you miss the part about it being helpful for restoring GI function after a bad disease? Things like dysentery and cholera were pretty common before modern times. An organism that can recover from diseases like this is going to live longer and pass on its genes more often. The downside of it occasionally causing appendicitis and killing the organism is likely a small risk in comparison: how often did people in pre-modern times (before they knew what it was and had the ability to do surgery to remove it) die of appendicitis? Not very often. It wasn't the main killer of people by a very long shot. But people got sick all the time from various things that affected the GI system.

[duncan_bayne]

You're uncharitably mis-reading my post, and being quite hostile in your reply.

What I meant was that - in hindsight - the fact that it had some beneficial function like restoring GI function should have been obvious, because otherwise, it would have been selected away.

That is, even a layperson _should_ have looked at the situation and thought "I bet it does something for us". But that's the benefit of hindsight; most (including myself) didn't. We just accepted the folk wisdom that it was useless.

[Arizhel]

Sorry, you're right, I misread your post. I think you have a good point here, but to be fair I don't think people weren't thinking in evolutionary terms at all. Not everything in our (or other animals') bodies are actually there for a good reason now. I'll give you one good example: horse toes. I don't remember the exact term now, but horses equine ancestors used to have multiple toes, like us and many other mammals. Now they just have one, with a big fingernail, called a "hoof". But if you look closely at the anatomy of their legs, you'll see some of the vestigial toes still there, serving no useful purpose now. Evolution isn't like engineering design, where we improve a design, see something that's not needed any more (like an automotive engine distributor), and just remove it entirely, and everything related to that, in one clean sweep, even mundane small things like bolt holes, and optimize the design for the new system (being coil-on-plug for this analogy). With evolution, it's slow and gradual. Another example is the recurrent sublaryngeal nerve in humans: this nerve apparently takes a rather bewildering and inefficient route, for seemingly no good reason, but when looked at from an evolutionary perspective, it makes sense why it takes that route. (The nerve itself is not vestigial and serves an important purpose, but the route it takes is very sub-optimal and could be called "vestigial" in a way.)

[1] http://www.thehorse.com/articles/34382/where-did-horses-extr...

[2] https://unzipyourgenes.wordpress.com/2011/03/24/unintelligen...

So I think it's entirely reasonable, in the absence of contradictory evidence, to use evolutionary thinking to make an argument that an anatomical structure seems to serve no purpose any more, just like those extra horse toes. Unfortunately, they were obviously wrong about the appendix, and I do think it's a little dangerous because the assumption of vestigiality rests upon the lack of evidence for the part having a modern use, but this can cause people to stop looking for that modern use, and then we wind up with what happened to the appendix, where it took a really long time to learn the truth because we assumed we already knew.

[duncan_bayne]

Agreed almost entirely - and I apologise for uncharitably calling your reading uncharitable :)

I think there is a subtle difference between the appendix and the horse toe, though: the appendix regularly kills people due to appendicitis. I _think_ that ought to have been a clue. Unsure though as it's not really my field.