[koan]

Assuming for a moment that there is a chicken, we are aware that the formation of such a thing takes place inside the protective shell of an egg. If the chicken precedes the egg then the first chickens were different than current chickens and evolved to the egg laying method. If so, then it was not truly a chicken yet and when the evolution happened the modern chicken was "born". Thus the egg precipitates the birth of the new species.

To say that they came from reptiles or another form of bird then includes that species into the question and the origins of the assumed relative becomes part of the question as well.