What Came First the Chicken or the Egg? This Is the Answer You've Been Looking For

What came first, the chicken or the egg? This age-old philosophical and scientific dilemma of whether the chicken or the egg came first has riddled a lot of us. Aside from being a scientific inquiry, t's a metaphor for the futility of discovering the root cause of a self-perpetuating loop.

Understanding the Evolution of Eggs

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The egg came first, according to most biologists. Eggs are simply female sperm cells at their most basic. Hard external eggs that can be laid on land (also known as amniotic eggs) revolutionized vertebrate evolution.

Prior to the development of hard-shelled eggs with nourishing yolks, animals had to reproduce in bodies of water. Most amphibians are still subject to this watery constraint, as they must keep their gelatinous eggs moist in order to survive.

"The egg is such an important step in [vertebrate] evolution, because it allowed amniotes to go further and further away from water," Koen Stein, a paleontologist at the Royal Belgian Institute of Natural Sciences.

In research published in the journal Current Biology, true birds did not appear in the fossil record until the mid- to late Jurassic period, some 165 million to 150 million years ago.

According to the University of Texas at Austin's Biodiversity Center, scientists believe the first shelled eggs originated 325 million years ago, which means that eggs came before chickens.

There were many land-based vertebrates that laid amniotic eggs during the Carboniferous, Permian, and Triassic periods, but the dinosaurs are the most famous of these species. Stein has researched some of the earliest known dinosaur eggshells from the early Jurassic period, some 200 million years ago.

The outer shells of these eggs were very thin, only about 100 microns thick. That thinness is possibly why academics have had difficulty identifying earlier examples of eggshells. When an egg comes into contact with rich, acidic soil, it begins to slowly dissolve.

First Chicken Egg

So, the egg existed before the chicken. Isn't the case closed? No, not quite. The story changes when we talk about the first chicken egg.

Around 50 million years ago, chickens (Gallus gallus domesticus) most likely originated from a subspecies of red jungle fowl (Gallus gallus). These birds were first domesticated by humans in Southeast Asia around 1650 B.C.

The last ancestor of modern chickens would have deposited an egg containing an embryo with enough genetic changes to distinguish it from its parent species at some point during the domestication process.

Before hatching, this embryonic chicken would have formed in the not-quite-chicken egg. Then, when it reached adulthood, it would lay the first normal chicken egg. The chicken could thus be considered to precede the chicken egg.

However, there is evidence that chickens interbred with other subspecies of jungle fowl even after they became their own genetically separate subspecies. Some of these characteristics are more (or less) pronounced in particular current chicken breeds.

According to the University of Wisconsin-Madison, chicken domestication appears to have occurred independently numerous times over several thousand years in portions of India and Oceania. As a result, distinguishing which chicken was the original can be difficult.