Which Came First?: Finding the Truth Behind the Riddle

Which came first: the chicken or the egg?

The question itself is ancient, posed long before forces in the natural world were well understood. Today, it is an oft used riddle with a knee-jerk answer based on faith and philosophy, a clever cover for a different question entirely—are you a creationist or an evolutionist? This stood as a divider between the scientific and religious worlds until, in late 2010, a certain meme began circling the internet proclaiming that scientists had cracked the case! Due to a protein found in eggshells that is only produced by hens, the chicken had to come first!


Could it be that we finally have a definitive answer backed by science? Is this really the end of the debate?

Well, as one of my professors in college always said, never trust ‘facts’ that come from a meme. My first reaction to these memes was skepticism, of course. Primarily because of my understanding of the processes of genetic mutation and speciation, I couldn’t fathom how any scientist worth their salt could come to this conclusion based on that evidence. But this information, whether true or falsified, came from somewhere, certainly, and so I made it my goal to get to the bottom of this conundrum.




To begin with, I would like to discuss the history of that definitive barnyard fowl, the domestic chicken. This topic tends to be quite triggering to people, and as a result tends to end up quite heated. But in actuality, it should not be. You see, as much as people like to use the chicken and egg riddle as a cover for the aforenoted philosophical question, it is not something that can truly serve that purpose. Chickens as we know them today were never found in the wild. Mankind didn’t go out to the forest one day and find a Barred Rock wandering around, deciding then to tame and keep it. Instead, they found the ancestral species of the domestic chicken, the Junglefowl (genus Gallus), and captured them to tame. The primary ancestor to today’s chicken is the Red Junglefowl (G. gallus) (Eriksson et al., 2008). Just looking at a Red Junglefowl, one can see the family resemblance.


However, chickens are not a pure descendant of these Red Junglefowl, and thus can’t be considered the same species. Genetic evidence suggests that Grey Junglefowl (G. sonneratii) were introduced into the bloodline as well, supplying the yellow skin gene that is common to many breeds today (Eriksson et al., 2008). Other Junglefowl species, such as Green Junglefowl (G. varius), may have also played a part in the creation of modern-day chickens, though many shared genes could also be attributed to modern interbreeding between feral chickens and these Junglefowl species, and thus their role in the creation of chickens is more difficult to determine (Sawai et al., 2010). The point still stands, however, that the chicken was not a wild species, but a selectively bred creation of mankind. And, because these Junglefowl species existed long before the domestication of the chicken, and as birds laid eggs before the domestic chicken existed, the egg must have come before the domestic chicken.

So, that’s it! Simple! We’re done, right? But the question remains, where did the information in those memes come from?




Taking a moment to search for key words found on any of the memes comes up with various news websites who are happy to keep spreading the ‘fact’ contained in these memes, but few seem to cite the work that concludes this. A search of scholarly articles including the lead author, Colin Freeman, mentioned in these news articles, along with the protein proclaimed only to be produced by chickens and thus meaning they must have come first, ovocleidin-17, results in numerous scholarly articles about said protein. Through these searches, and by checking the dates on news stories about the topic, I was able to locate the article responsible for this influx of ‘chicken or egg’ memes. That article is, “Structural Control of Crystal Nuclei by an Eggshell Protein”, by Colin L. Freeman, John H. Harding, David Quigley, and P. Mark Rodger (2010). Of course, this title makes no implications that the article answers that ancient riddle, and a look-through of the work also leaves attentive readers with no definitive answers on the topic. This is simply a paper about how the egg shells of chickens are formed so rapidly.


The answer lies instead in interviews of the authors. In several statements, Freeman has implied that this work indeed gives the answer we’re looking for. The protein ovocleidin-17 (OC-17) is found only in the shell gland secretions of the chicken (Freeman et al., 2010; The Uniprot Consortium, 2017; Berthold, 2018). This protein speeds up the process of constructing the egg shell, allowing a hen to lay an egg within 24 hours of beginning to construct it (Berthold, 2018). OC-17 is unique to chicken eggs—a chicken egg cannot be produced without it—meaning therefore that the chicken must have come before the chicken egg.

But, how can this be?




Looking at G. gallus next to a modern chicken, one can note many similarities, but also many differences. This is particularly true of some of the more uniquely patterned or shaped chicken breeds, such as Silkies. A comparison of the Silkie chicken to its wild ancestor gives nearly no similarities to draw. So how does one get from Red Junglefowl to Silkie chicken?


Beyond introducing genes such as by crossing a species to another closely related species, as with the mentioned introduction of the yellow skin gene by crossing in Grey Junglefowl (G. sonneratii), new genes may appear by a process called spontaneous mutation. Despite what movies and comics might imply, mutations don’t necessarily have to coincide with exposure to chemicals or radiation. Spontaneous mutations are mutations that occurs by natural processes, not by exposure to such mutagens (Dictionary.com, n.d.). In other words, they are a random change in DNA not caused by an outside force. These so-called ‘natural mutations’ occur infrequently and are often removed by natural selection before they can establish in a population (Huang et al., 2016). This is mostly because when DNA changes randomly, it’s most often lethal; it is, after all, essentially a ‘typo’ in the formula used to build a living thing.

Very rarely, a spontaneous mutation is non-lethal, but may or may not cause a trait that is desirable in a wild population. Over the several thousands of years that chickens have been kept by man, any number of these mutations could have occurred. No amount of intervention can change the loss of lethal or otherwise physically harmful genes from a population (Huang et al., 2016). However, human intervention can allow for the proliferation of otherwise undesirable traits in a population by means of, for example, protection from predators who may find certain feather colors more conspicuous than others, or providing shelter to birds whose feather shape may leave them more vulnerable to extreme weather. What would cause mankind to select undesirable traits for survival such as those found on a Silkie? That’s anyone’s guess—though given the popularity of frilly, pretty, or entirely decorative breeds, it could be assumed that someone just decided that they liked what they saw and continued to breed it.

Now, we know that this protein, OC-17, the production of which would almost inevitably be thanks to a spontaneous mutation occurring, is what allows a hen to produce an egg in a relatively short time period. It stands to reason that it would be a desirable trait for early chicken breeders to select for in their flocks. A bird that lays more eggs will obviously have more offspring, and will feed its keeper’s family better than one that lays fewer eggs. Thus, the modern chicken was produced through mankind's selection for highly productive individuals and, in a roundabout way, for the production of OC-17.




If you’ve made it this far, you may still be puzzling out whether I'm leading to those meme ‘facts’ having any truth to them after all. The answer really is dependent on context. Yes, you could technically say, from all the above rambling, that the chicken came first. However, chickens are a relatively recent addition to the world, and birds existed long before they did, and laid eggs long before they could. That said, no bird before the chicken truly laid chicken eggs because chicken eggs include the protein OC-17 that allows them to build eggshells faster.

So, to make a terribly long story short, the bottom line is this: The egg came before the chicken, but the chicken came before the chicken egg.

In the end, I believe a coauthor of the study that started up all these memes, P. Mark Rodger, said it best (University of Warwick, 2010):