Chicken and the egg debate ends here
Everyone must have indulged in this debate at least once which ended in the dilemma stating "which came first - chicken or the egg?"
Yes, the egg came first.
In nature, living things evolve through changes in their DNA. Chickens, as a species, became chickens through a long, slow process of evolution. At some point, a chicken-like bird produced an offspring that, due to some mutation in its DNA, crossed the threshold from mere chicken likeness into chicken actuality. That is to say, a proto-chicken gave birth to a real-life official chicken. And since that real-life official chicken came out of its own egg, we can say that the egg came first.
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Another way to look at the question would be to ask which came first in evolutionary history. Once again, the egg takes precedence. Many characteristics of the modern avian egg - namely an oblong, asymmetrical shape and a hardened shell - were in place before birds diverged from dinosaurs about 150 million years ago.
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Chickens evolved from non-chickens through small changes caused by the mixing of male and female DNA or by mutations to the DNA that produced the zygote. These changes and mutations only have an effect at the point where a new zygote is created. That is, two non-chickens mated and the DNA in their new zygote contained the mutation(s) that produced the first true chicken. That one zygote cell divided to produce the first true chicken.
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Prior to that first true chicken zygote, there were only non-chickens. The zygote cell is the only place where DNA mutations could produce a new animal, and the zygote cell is housed in the chicken's egg. So, the egg must have come first.
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Source: Popular Science