Originally Posted by Matt Harris
In one sense it stands to reason that an egg has evolved to not being turned, then you shouldn't turn it, and reading about the structure of reptile eggs, I can see how turning could damage them, as Ian says above. However, I've never seen any research which provides evidence that turning eggs kills the embryo, and if so, why.
It seems to me that the advice not to turn reptile eggs is based on assumption rather than proof, although it's probably a correct assumption.
What is needed is someone to take a whole load of eggs and turn some of them to differing extents and at differing times during incubation, and compare hatching rates with a control sample.
I am pretty sure that it has nothing to do with an assumption, but due to the physiology of the egg - by being turned the embryo becomes detached from the shell. The shell is porous to allow gas and water vapour transfer, with blood vessels attached to the shell itself. When I get 5 minutes I'll have a look in one of my old uni textbooks, I am sure it was in there. To clarify, turning vertically has nothing to do with it, turning full stop can cause the embryo to detach.