What came first? The chicken or the egg?

This is frequently given as the quintessential unanswerable question. But the question isn’t unanswerable because we lack sufficient knowledge; it is unanswerable because the question is ambiguous. It is pretty tough to come up with an answer if you don’t understand the question.

In this case, we need clarification about what exactly is meant by the words "chicken" and "egg." With the help of Merriam-Webster Online we can rewrite the question as follows:

Which came first, the common domestic fowl (Gallus gallus) or the hard-shelled reproductive body produced by a bird and especially by the common domestic chicken?

Restated in this precise fashion, the answer is very straightforward. The  common domestic fowl was bred from the wild Red Jungle Fowl approximately 8,000 years ago by people living in what is now Southeast Asia.

Since the egg, as defined by Merriam-Webster, is found in all birds (including the common domestic chicken), then we have to go back to the common ancestor of all birds to find the first bird egg. Since this common ancestor was alive well over 150 million years ago, it seems pretty clear that the egg came first.

Of course, there are different definitions of the word "egg." If you happen to be a fan of the MSN Encarta World English Dictionary, then our question would be rewritten as:

Which came first, the common domestic fowl (Gallus gallus) or a large sex cell produced by birds, fish, insects, reptiles, or amphibians, enclosed in a protective covering that allows the fertilized embryo to continue developing outside the mother’s body until it hatches?

Based on this definition, in order to find the first egg you would have to go back over 500 million years to find the common ancestor of birds, fish, insects, reptiles, and amphibians. In other words, the egg clearly came first.

Scott M. Lanyon
Director, Bell Museum of Natural History
Professor, Department of Ecology, Evolution, and Behavior