What came first: The chicken or the egg?

Scientific Evolution and Origins Prove “Team Egg” 

The old question — “Which came first, the chicken or the egg?” — has been around forever, sparking debates over dinner tables and long walks. It sounds simple, but it’s actually a bit of a mind-bender: you need a chicken to lay an egg, but chickens come from eggs… so what gives?

It’s one of those loops that feels like it has no real answer — until science steps in. Evolutionary biology, with all its slow, fascinating twists, actually helps us crack the mystery.

The Evolutionary Journey of Eggs

• An egg is simply a membrane-bound vessel inside which an embryo can grow and develop until it can survive independently. Eggs of various shapes and sizes exist throughout the entire animal kingdom.
• However, the type of bird’s egg commonly recognised today first appeared with the evolution of the first amniotes many millions of years ago. Before their emergence, most animals relied on water for reproduction, laying their eggs in moist environments like ponds to prevent them from drying out.
• A pivotal evolutionary development was the emergence of a different kind of egg that included three extra internal membranes: the chorion, amnion, and allantois. These additional layers formed a conveniently enclosed, all-in-one life support system for the developing embryo:
  • The embryo could take in stored nutrients.
  • It could store excess waste products.
  • It could respire (breathe) without the need for an external aquatic environment.
  • Furthermore, the extra fluids encased in the amnion, combined with a tough outer shell, provided additional protection.
• These amniotic eggs were a “big deal” as they opened up a whole new world of opportunities for land-based egg-laying locations and paved the way for larger and often more developed eggs.
• While the exact timing of this evolutionary event is not perfectly clear due to eggy membranes not preserving well as fossils, the best scientific estimate is that the last common ancestor of both tetrapods (four-limbed animals with a backbone) and amniotes lived around 370-340 million years ago. Some sources, however, suggest the first amniote species appeared closer to 312 million years ago. Significantly, today’s mammals, reptiles, and birds are all descendants of these early amniotes.

The Emergence of Chickens

• Two “almost-chickens” or “proto-chickens” mated and produced a zygote, in which one or more genetic mutations gave rise to the very first “true chicken.” These initial mutations in that first cell would then have copied themselves into every subsequent body cell as the chicken embryo grew and developed.
• The red junglefowl (Gallus gallus) is considered the closest ancestor to the modern domestic chicken (Gallus gallus domesticus). This species is native to various Southeast Asian countries, including India, southern China, Indonesia, Malaysia, and Singapore. Humans in Asia domesticated the red junglefowl, which then spread globally and evolved into the less-aggressive, prolific egg-layers we know today.
• Archaeological evidence suggests this domestication occurred around 10,000 years ago. However, more recent DNA analysis and mathematical simulations propose a much earlier divergence of the domestic chicken from junglefowl, estimated 58,000 years ago. There is also evidence suggesting a more complex origin, with genes for the yellow leg colour found in many domestic chickens. These genes possibly originated from the grey junglefowl (Gallus sonneratii), indicating some hybridisation between species along the way.

The Egg Came First

• By comparing the evolutionary timelines, the answer becomes clear: with amniotic eggs appearing roughly 340 million years ago (or even earlier), and the first chickens evolving at the earliest around 58 thousand years ago, it is a conclusive fact that the egg came first. Simply put, eggs were around long before chickens even existed.

The “Chicken First” Argument and Clarification

• Interestingly, some researchers previously claimed that the chicken actually came first. This argument stemmed from studies on how chicken eggshells form. Hens obtain calcium from their diet and use it to form eggshells primarily made of calcium carbonate (CaCO₃).
• The process of depositing calcium as CaCO₃ crystals relies on specific proteins. One such protein, called ovocleidin-17 (OC-17), is found exclusively in the ovary of a chicken. This led to the suggestion that without OC-17, a chicken egg could not form. That implying the chicken must have preceded the chicken egg. It’s worth noting that OC-17 also appears to be responsible for speeding up eggshell formation that enabling hens to produce an egg within a 24-hour timeframe.
• Scientists ultimately consider the question a false dichotomy. While eggs (in their general, evolutionary sense) certainly came before chickens, it is true that a chicken egg specifically cannot exist without a chicken. However, when forced to choose based on the overwhelming evolutionary evidence provided, science definitively sides with Team Egg.

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Is Eating Chicken Healthier Than Eggs?

Both chicken and eggs are incredibly nutritious, but they each bring something different to the table. Lean chicken is a great source of high-quality protein and important vitamins like B3 (niacin), making it a solid choice for building muscle or maintaining a low-calorie, high-protein diet. It’s also rich in minerals like phosphorus and selenium, which support bone strength and a healthy immune system. Eating chicken regularly, as part of a balanced diet, can help with weight management and keep your energy levels steady throughout the day.

Eggs, on the other hand, are a powerhouse of nutrients packed into a small package. They offer a good balance of protein, healthy fats, and essential vitamins like D and B12. Plus, they contain minerals such as iron and selenium, and antioxidants that benefit your eyes and overall health.

In the end, whether chicken or eggs are “healthier” really depends on your personal health goals and dietary needs—both can be excellent additions to a healthy lifestyle.