Chick or Egg, which came first - a debate no more?

This famous question, whose origin can be traced far back into the Greek philosopher Plutarch's Moralia at the beginning of the first millennium, has been much used and abused over the course of the history since then. Finally, in a debate organized by Disney to promote the DVD launch of its film "Chicken Little", a team comprising a geneticist, a philosopher and a chicken farmer appears to have cracked the puzzle.

First, to clarify the debate itself - the egg of course refers to a chicken egg, and not any other egg such as an ostrich egg, else there is no debate to begin with. But what is the definition of a chicken egg? There are in fact three definitions. First, an egg from which a chicken is hatched. Second, an egg laid by a mother hen. And third, an egg laid by a hen from which a chick is born. There seems to be no doubt about the first definition. And if one also assumes the second, then the third definition is redundant. The first two definitions toegther, however, gives rise to the circularity, and hence, the debate on which came first. So, in order to break the circularity, one of them must have been wrong when the first chick or the first egg appeared. But which one?

Therein comes Darwin's evolution (what else?) to the rescue, and a simple fact of genetics. The answer seems to be almost straightforward in hindsight. Evolution teaches us that all species, including our chicken, derived (or speciated, using technical jargon) from an ancestral species. And genetics tell us that an individual's genetic makeup does not change during its lifetime. Therefore, the ancestral "pre-chicken" individual could not have metamorphosed into a modern hen as it was growing up, and instead the changes must have happened within the egg during the earliest stages of embryonic development, when rapid chromosomal mixing was taking place. To put it simply, the first chicken egg was laid, not by a hen, but by a "pre-hen". And therefore, egg came first, and the chicken followed.

The argument might still appear preposterous to many were it not for a sobering fact of evolution, which is the underlying continuity of changes as a species moves up its evolutionary ladder. (There are glaring exceptions, as the huge gaps in the fossil records stretching back to a few billion years bear testimony to, but that is a whole different story). We humans did not arrive overnight from tree-hopping monkeys, but progressed through a series of intermediate species over millions of years. Likewise, the ancestor of the hen might have been quite like the hen itself, and probably did not even spot the odd chick as it mingled happily with the rest of its nestlings.