The answer, IMHO, is that "a chicken" was born from an egg put by a "non-chicken". And the thing is, you could not determine when exactly the non-chicken becam

The answer, IMHO, is that "a chicken" was born from an egg put by a "non-chicken". And the thing is, you could not determine when exactly the non-chicken became the chicken i.e. when it is chicken enough. You could not draw a line.