Chicken Nugget: Wind Eggs

April 21, 2009 at 10:35 pm | Posted in Poultry | Leave a comment

One of the leading medieval experts on chickens was Ulisse Aldrovandi. During the mid to late sixteenth century he wrote a great many books, one of which Ornithologiae was praised by Darwin several centuries later. This huge work on birds encompassed vast swathes of knowledge about avian history. Book XIV has been translated into modern English under the title Aldrovandi on Chickens, and I have been slowly reading through it.

The work is typically medieval and typically frustrating. One moment Aldrovandi is walking the reader through a surprisingly sophisticated understanding of chicken reproductive anatomy, then on the next page he gives a serious discussion of eggs that have been fertilized by the wind.

Wait, fertilized by the wind? That’s right. Aldrovandi and his contemporaries had lots of practical experience with the concept that sperm + woman = babies. And they were well aware that eggs turned into babies. It makes sense that they jumped to the conclusion that sperm + hen = eggs. However Aldrovandi was working on incomplete knowledge. Mammal egg cells are microscopically small, so it is impossible that medieval thinkers could have realized that the actual equation would be more accurately represented as sperm + egg = babies. Just as with humans, birds produce the egg first, which is then fertilized (or not) by the male sperm. But where a human (or other mammal) ejects an unfertilized egg that is undeveloped and invisible to the naked eye, birds eject unfertilized eggs that are fully formed and visibly no different from viable eggs. (For those of you who eat supermarket eggs and are occasionally worried that you’re keeping a chick from being born, don’t worry: supermarket eggs have not been fertilized.)

So in the medieval world, the naturalists observed that chickens laid eggs. Since, in their minds, all eggs must be fertilized, there was, naturally, a need to understand and explain why not all eggs produced chicks. The obvious explanation: the wind was fertilizing the eggs, but since the wind is not sufficiently vital, the eggs do not hatch. It’s a wonderfully creative solution to a problem, even if it is entirely wrong.