Each term in the question requires the other. In a way, it's similar to "What is the sound of one hand clapping": an ancient paradox designed to stop the rational mind as an aid to "enlightenment."
In the case, I think it was designed by someone opposed to evolution to stop discussions on the subject.
There's a story about a teacher and a young child. The teacher was saying how the world is flat. The child was very bright and asked a question few students did. "Then what holds up the world?" The teacher said, "It sits upon the back of the great world turtle."
That answer had always satisfied his smartest students. It referred to something completely beyond personal experience but having a familar shape. But this student was very smart and asked, "But what does the turtle stand on?" The teacher was very clever and said, "From there it is more turtles all the way down."
So, this question is really based upon the paradox of infinite nature of the chain of cause and effect. It asks for the cause that starts the entire chain. It's one of the principal philosophical arguments for the existence of "God" as the "First Cause."
However, the question is really unanswerable because of the contradictions hidden in the terms. On one side is the idea of an endless chain of cause and effect running infinitely back into the past and forward into the future. On the other, it supposes an inital cause. But on the other side, every cause is seen as the effect of a preceding cause. Thus, the contradition..
Now, from a biological perspective a chicken comes from an egg. Normally from a chicken egg. But we can imagine a proto-chicken (almost a chicken) that laid an egg in which a mutation occurred. So, only within the field of evolutionary biology we can say, EGG.
Otherwise, we have the First Cause paradox.
--Jimi Li
It's questions like this that makes philosophers fun to drink beer with.
