The chicken or the egg dilemma is a commonly stated question, “which came first: the chicken or the egg?” The dilemma comes from the observation that all chickens hatch from eggs and all chicken eggs are laid by chickens. “Chicken-and-egg” is a metaphor describing situations where it is not clear which of two events should be considered the cause and which should be considered the effect, to express a scenario of infinite regression, or to express the difficulty of sequencing actions where each seems to depend on others being done first.
Although the question is typically used metaphorically, biology provides literal answers, made possible by the Darwinian principle that species evolve over time, and thus that chickens had ancestors that were not chickens.
If the question was referring to eggs in general, the egg came first. The first egg – that is, a hard-shelled egg that could have been laid on land, rather than remaining in water like the eggs of fish or amphibians. Chickens are domesticated descendants of red junglefowl and probably arose little more than eight thousand years ago.
