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Scientists Conclude the Age-Old Debate That the Chicken Came Before the Egg

The universities of Bristol and Nanjing discovered chickens existed before chicken eggs, reproducing through extended embryo retention.

Extended embryo retention could solve the chicken or the egg paradox.
"The chicken or the egg," has been asked by scientists and philosophers for centuries. Extended embryo retention might be the answer. Credit: Shutterstock/LukFu

According to the study published in Nature Ecology & Evolution, the evidence indicates that basal archosauromorphs, the ancestors of modern-day archosaurs such as birds and crocodilians, reproduced through live birth, as well as a process called extended embryo retention.

In this process, mothers would retain their young to a certain point before releasing them, rather than laying hard-shelled eggs wherein the embryos could grow and evolve further.

“EER is common and variable in lizards and snakes today,” Dr. Joseph Keating said in an interview with Science Daily.

“Their young can be released, either inside an egg or as little wrigglers, at different developmental stages, and there appears to be ecological advantages of EER, perhaps allowing the mothers to release their young when temperatures are warm enough, and food supplies are rich.”

Professor Michael Benton, one of the study’s researchers, explained to NPR that for years, the consensus was the first reptile laid hard-shelled eggs, giving their embryos the ability to grow while encapsulated within a private pond, rather than amphibians, which are constrained to the water.

“So the whole business in the story of the evolution of life was some time in the Carboniferous, 300 million years ago, some of the earliest reptiles got this ability to get away from the water and therefore to conquer the whole of the landscape. Wrong. It wasn’t the private pond. It was the extended embryo retention and live birth. That seems to be the primitive state for reptiles.”

The team reached this conclusion by studying 80 amniotic species, 51 from fossils and 29 from living species, all of which exhibit signs of viviparity and extended embryo retention.

Supporting evidence

These findings are further corroborated by an earlier study, also published by Nature in 2020, which suggests that the first eggs were soft rather than hard-shelled, a possible indication of extended embryo retention.

In addition, another study conducted by Sheffield and Warwick Universities in 2010 found that a key protein in egg production, ovocledidin-17, was produced in chicken ovaries. Before the study, the protein’s purpose was unknown.

“What we have really identified is that the protein seems to accelerate the crystallization process, so it can make that eggshell appear far quicker,” Dr. Colin Freeman said in an interview with CNN.

“In simple terms, it accelerates calcite formation,” giving chicken eggs their rigid structure and again indicating chickens existed before they could lay eggs.

Given the evidence, one has to wonder how and why the argument persists despite the research. According to paleontologist Koen Stein in Live Science, “When an egg encounters rich, acidic soil, it begins to slowly dissolve,” which makes it much more difficult to collect soft-shell samples versus the hard-shell variety.

To compound with the rigors of collecting data, these studies are also just a few attempts at solving the age-old mystery. Other researchers have produced widely different conclusions, albeit from different perspectives.

Past counterarguments

Before the study, it was believed that chickens came into being from mixing two proto-chickens. From there, the offspring would develop within the egg and hatch with the characteristics we associate with living chickens.

While it could be argued if said egg qualifies as a chicken egg or a proto-chicken egg, David Papineau of King’s College London explained to the Guardian that

“If a kangaroo laid an egg from which an ostrich hatched, that would surely be an ostrich egg, not a kangaroo egg. By this reasoning, the first chicken did indeed come from a chicken egg, even though that egg didn’t come from chickens.”

In another study from 2018, quantum physicists from the University of Queensland focused on solving the question from a theoretical angle.

“By measuring the polarisation of the photons at the output of the quantum switch, we were able to show the order of transformations on the shape of light was not set,” according to Dr. Fabio Costa.

In other words, cause-and-effect cannot be rigidly defined, and it is theoretically possible for both the chicken and egg to come first, physically speaking.

With all that said, it is unlikely the debate will end with this most recent study, as any future research could potentially add to the current theory or completely upend it, depending on the results.

“It’s a classic pub quiz question. So whether it’s like the why did the chicken cross the road, I’ve got no idea. But I expect people will keep asking and keep answering it in different ways,” Benton said.

Written By

Southern California, born and bred. I earned my bachelor's from Cal Poly Pomona, but I first got my feet wet at Citrus College after graduating from Bonita High School. I love learning about the world and sharing my findings. When I'm not doing that, I'm either chipping away at my gaming backlog or catching up on my reading.

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