History of the dilemma
Ancient references to the dilemma are found in the writings of classical philosophers. Their writings indicate that the proposed problem was perplexing to them and was commonly discussed by others of their time as well.
Aristotle (384–322 BC) was puzzled by the idea that there could be a first bird or egg and concluded that both the bird and egg must have always existed:
The same he held good for all species, believing, with Plato, "that everything before it appeared on earth had first its being in spirit."
Plutarch (46–126) referred to a hen rather than simply a bird. Plutarch discussed a series of arguments based on questions posed in a symposium. Under the section entitled "Whether the hen or the egg came first", the discussion is introduced in such a way suggesting that the origin of the dilemma was even older:
Macrobius (early 5th century), a Roman philosopher, found the problem to be interesting:
In System of Nature by Baron D'Holbach (1770, translated into English in 1797), he asks "was the animal anterior to the egg, or did the egg precede the animal?" (part 1, chapter 6).
Stephen Hawking and Christopher Langan argue that the egg came before the chicken, though the real importance of the question has faded since Darwin's On the Origin of Species and the accompanying Theory of Evolution, under which the egg must have come first, assuming the question intended "egg" to mean an egg in general rather than an egg that hatches into a chicken. According to Popular Science, the egg came first as it evolved prior to birds.
Responses to the dilemma
Professor Charito Sulatar and David Quigley, from the University of Warwick, who helped develop a study with colleagues from Sheffield University, point out that in fact a key chicken protein, ovocleidin-17, which helps in the formation of the egg's hard shell, actually comes both before and after the egg shell. They say that this chemical quirk actually makes the question of which came first even more pointless than before. As Professor Mark Rodger says, "Does this really prove the chicken came before the egg?" This science does give new insight into an efficient and fast method of crystallization. It will help in research to devise better synthetic bone and research into how to store/sequester CO2 as limestone."
A previous analysis which came to another conclusion. Professor John Brookfield and Professor David Papineau argue since there was a "first" chicken, it must have come from an egg which pre-dated that chicken. An even earlier analysis which also came to another conclusion was made by Roy A. Sorensen in his one-page-article in 1992. He argued that although it is indeterminate which animal was the first chicken, the question of whether the chicken or the chicken egg came first has a determinate answer. Since an animal does not evolve into another species during its lifetime, and since organisms can fail to breed true, it is biologically necessary that the chicken egg came first. Biologist PZ Myers points out a further flaw in the 'protein-argument', in that other birds make use of different kinds of proteins for producing eggs, and that the evolution of ovocleidin was not coincident with the evolution of eggs; ovocleidin developed from prior proteins, which were used to form eggs since before birds branched away evolutionarily from reptiles.
Main article: Evolution
The theory of evolution states that species change over time via mutation and sexual reproduction. Since DNA (deoxyribonucleic acid) can be modified before and after birth, it can be argued that a mutation must have taken place at conception or within an egg such that a creature similar to a chicken, but not a chicken, laid the first chicken eggs. These eggs then hatched into chickens that inbred to produce a living population. Hence, in this light, both the chicken and the structure of its egg evolved simultaneously from birds that, while not of the same exact species, gradually became more and more like present-day chickens over time.
However, no one mutation in one individual can be considered as constituting a new species. A speciation event involves the separation of one population from its parent population, so that interbreeding ceases; this is the process whereby domesticated animals are genetically separated from their wild forebears. The whole separated group can then be recognized as a new species.
The modern chicken was believed to have descended from another closely related species of birds, the red junglefowl, but recently discovered genetic evidence suggests that the modern domestic chicken is a hybrid descendant of both the red junglefowl and thegrey junglefowl. Assuming the evidence bears out, a hybrid is a compelling scenario that the chicken egg, based on the second definition, came before the chicken.
This implies that the egg existed before the chicken, but that the chicken egg did not exist until an arbitrary threshold was crossed that differentiates a modern chicken from its ancestors. Even if such a threshold could be defined, an observer would be unlikely to identify that the threshold had been crossed until the first chicken had been hatched and hence the first chicken egg could not be identified as such.
A simple view is that at whatever point the threshold was crossed and the first chicken was hatched, it had to hatch from an egg. The type of bird that laid that egg, by definition, was on the other side of the threshold and therefore not a chicken—it may be viewed as a proto-chicken or ancestral chicken of some sort, from which a genetic variation or mutation occurred that resulted in the egg being laid containing the embryo of the first chicken. In this light, the argument is settled and the 'egg' had to have come first. However, whether this was defined as a chicken egg or proto-chicken egg is debatable. So technically the egg came before the chicken, but the chicken may have come before the chicken egg. So it depends on whether the question is "What came first, the Chicken or the egg" or "what came first, the Chicken or the Chicken egg".
Logically the final conclusion can be drawn that the egg indeed came before the chicken, as a bird that was not a chicken could accumulate germline mutations in a single sperm or ovum to produce the first genetically identifiable chicken, but a non-chicken egg is much less likely to produce a non-chicken which accumulates enough identical somatic cell mutations across its cells to create a chicken spontaneously.
Philosophy of Science
An author writing under the name Joseph Bonilla (a pen name) has argued that, from the perspective of the Philosophy of Science, the above answers to this question are all mistaken. Stephen Hawking and Neil DeGrasse Tyson have both come out in favor of the egg, but they have both missed certain important considerations. (The author, like Chris Langan, also has an IQ over 150). In his paper, he argues that the answer is ultimately not knowable. His paper is available on SSRN, and he has said that he has discussed his paper with Prof. Jeffrey Barrett of the University of California at Irvine, the editor of the journal "Philosophy of Science".