The biggest and most famous causality dilemma known to man, dating back to the time of the ancient Greeks, the dilemma that left your head spinning, finally has an answer!! (A causality is the relationship between an event (the cause) and a second event (the effect), where the second event is a consequence of the first).
Everybody knows you need a chicken to produce an egg, you need an egg to produce a chicken. But nobody knows how the cycle started.

Think back! What was your answer to the question? I’m sure most of you reading this wouldn’t have given much thought to the dilemma and its underlying secret. (Including me, until now). But fortunately for us, there exists among us, people who ponder all night to find a rational solution to the problem.
Let’s take a look at the real theory behind this, from an evolutionist’s point of view.
Long before chickens came into existence, there were other types of birds which evolved from reptiles, both of which are egg-laying animals. So technically, the egg came before the chicken. Now we have a problem as to which egg we’re referring to, is it a general egg or a chicken egg? Studies have shown that the protein essential for the formation of chicken eggs, OV17 is only found in chicken ovaries. Without it, the chicken eggshell could not be formed and technically you cannot get a chicken egg without a chicken. So this inserts a whole new question into the picture. Is a chicken egg one that is laid by a chicken or only one that simply contains a chicken? (The two scenarios are discussed later).
According to AsapSCIENCE by Mitchell Moffit and Gregory Brown, long long time ago, there were chicken-like birds which were genetically similar to a chicken, and we call them proto-chickens. A proto-hen would have mated with a proto-rooster to form a zygote. And as most of you know, replication of DNA is not always accurate, minute changes in base sequences in the DNA molecule may occur during replication and formation of daughter cells. These minute changes are called mutations and can give rise to a new species in the process called evolution. Such a mutation might have occurred while producing the sperm or egg cell of the proto-chickens. When they fertilized and fused to form the zygote, it carried with them this small genetic mutation to the offspring which created the first chicken instead of a proto-chicken. So the egg came first. But some may argue that this chicken came out of a proto-chicken egg and thus this theory is not acceptable. However, no single mutation can really give rise to a whole new species. It’s a long and gradual process, longer than the life span of Noah!
So we’re left with two scenarios.
(1) Some early egg-laying species gradually evolved into the proto-chicken which laid a proto-chicken egg. In one of these eggs, there was a mutation that gave rise to a chicken inside the egg. This chicken had a selective advantage over the other proto-chickens and survived to lay a chicken egg. In this case, the chicken came first.

(2) The proto-chicken gave birth to a chicken which grew inside what we consider a chicken egg. So the egg came first.

This leads us to the question of what is a chicken egg? Is a chicken egg one that is  laid by a chicken or only one that simply contains a chicken? Regardless of the nomenclature of the egg, the first true chicken came from an egg!
If you get this logic, you should be proud of yourself!

References:
http://www.themasterg.com
http://www.swamij.com
http://www.youtube.com
http://www.mnn.com