Some years ago, I heard a joke that went roughly as follows:

A mechanical engineer, an electrical engineer, and a civil engineer are sitting in a pub. Says the mechanical engineer: "I think God must be a mechanical engineer. Just look at all those bones, muscles, tendons, joints and how it all interacts so nicely." - "Well, but nothing would be moving if it weren't for the brain and the nerves.", throws in the electrical engineer. "No, I think God is an electrical engineer." - The civil engineer takes a sip from his pint and then says: "You're both wrong. God is without any doubt a civil engineer." - "Why's that then?" - "Only a civil engineer would run a wastepipe straight through a recreational area."

So much for the joke. Now over to my question: I was wondering if this 'wastepipe-straight-through-recreational-area' is actually a universal feature in animals - or are there any animals where the 'wastepipes' and the 'recreational areas' are clearly separate?

I'm not sure about invertebrates, but I don't know of any vertebrates that separate the "wastepipe" from the "recreational area". In fact - not to get too graphic - most vertebrates display even more questionable engineering than humans and other placental mammals, which at least have the anus well separated from the urinary and genital openings. In birds, reptiles, amphibians and monotremes (the echidna and platypus), and in some fishes and marsupials, all three systems empty into a common orifice called the cloaca. This term comes from the Latin for sewer, so the cloaca is a wastepipe indeed. Surely not even a civil engineer would build something so inelegant - but evolution, which is blind to everything but the hard practicalities of survival and reproduction, is another matter.

A similar "engineering mistake" also exists at the the other end of the body where the GI and respiratory tracts cross in the mouth. From an engineering point of view I'd say it would be better to keep these tracts completely separate since while swallowing air may not be too bad, inhaling food and/or water can be lethal.

Hi Klaus,

this question relates to one we have discussed before: http://www.askabiologist.org.uk/punbb/v … php?id=653

Certainly there are invertebrates that separate their reproductive and waste "hardware". Many simple worms and endoparasites excrete through their body wall and release reproductive material through pores unconnected to the reproductive system. Insects such as wasps have more clearly segregated reproductive and waste systems - the ovipositor is sometimes adapted to deliver toxins, but not waste.