An eggcellent design
Eggshell nanostructure shows purposeful construction
The question of whether the chicken or the egg came first has been asked for thousands of years.1 However, any reader of Genesis will readily see that the answer is the chicken (or more accurately the landfowl kind), created on Day 5, which then laid an egg.
Renowned evolutionist David Attenborough, who denies any role for God in the egg’s design, has nonetheless described eggs as “miracles of nature” and the egg as “an excellent life support system”.2 The eggshell not only protects the chick developing inside, it acts as a semipermeable membrane that lets air and moisture pass through about 7,000 pores in a controlled fashion. This allows the chick inside to breathe, while protecting it from drying out due to a net loss of water.3
Now details of the first ever nanostructure examination of fully formed eggshells of the domestic chicken, Gallus gallus domesticus, have been published showing superb design in their formation, function and dissolution.4
Researchers from McGill University were able to accurately cut thin slices of the eggshell and “found that a factor determining shell strength is the presence of nanostructured mineral associated with osteopontin, an eggshell protein.”5 Osteopontin was discovered to be a binding agent, helping to form the superstructure of the eggshell, guiding the framework and controlling the arrangement of the calcium carbonate in the shell. In the outer layer of the eggshell, there were high levels of osteopontin, meaning that the structure is more closely and densely formed. This keeps the hard shell protective on the outside while the chick is getting ready to hatch. However, in the inner layer of the eggshell, there were lower levels of osteopontin. This means the nanostructure was larger and more loosely arranged, which made the calcium carbonate more accessible and thus allowed the inner layers to dissolve more readily.
Eggshells and tiny teeth
by Jenny Arms
Adding to these marvels of the eggshell’s purposeful design is the ingenious tool the tiny chick needs to break out to freedom—the ‘egg tooth’. This is a horny protrusion on the tip of its upper beak that starts to develop on day 7 of its gestation.
Some three days before hatching, the growing chick is finding it hard to get enough oxygen through the pores in the shell, so it uses its ‘toothed’ beak to slice a hole through the membrane into the air sac at the shell’s flatter end. This stored air gives it just enough extra oxygen to cope with the coming task of ‘breakout’.
At the right time, a muscle behind the chick’s neck begins spasming, encouraging it to ‘pip’ through the outer membrane and shell with its tiny ‘tooth’ tool. Thousands of times it chips the shell, rotating counter clockwise at its flatter end. This mammoth task requires hours of rest between bursts of activity.
Finally, it happens! Fresh air. Success! With one huge kick, the chick is born—exhausted, wet and sticky. The ‘tooth’ gradually shrivels and falls away, culminating this unique and purposeful process, the information for which was programmed into its DNA all along.
Jenny Arms is a retired Australian high school teacher (both secular and Christian) who lives in rural Victoria.
Two reasons for dissolution
Hatching is the climax of the egg’s experience, and the nanostructure of the egg demonstrates its wonderful dual-function design allowing the chick to hatch. The inner layer of the eggshell changes as the embryo grows and develops inside. The developing chick requires calcium to help form its bones, and it obtains this through dissolving the innermost layer of the eggshell.
In addition to helping the chick develop its bones, this dissolution also weakens the shell from inside, allowing the chick to be able to hatch when it comes to maturity, normally at 21 days.
Studying this process at the nanostructure level has made this design feature more fully understood. The research team highlighted that, “Such a process would allow retention of overall shell layer structure but with some thinning and compromised strength, a feature ultimately necessary for successful chick pipping to puncture/break the shell during hatching”.
These latest nanostructure findings have been acclaimed as useful in the design and strengthening of bioinspired material, as well as helping to understand controlled solubility in biostructures. The finding will also be of particular importance to the agri-food industry as “eggshell quality is a major concern to the poultry industry since the percentage of broken or cracked (with possible microorganism invasion)6 eggshells can range from 13% to 20%.” One of the paper’s authors, Dr Marc McKee, explained that, “Understanding how mineral nanostructure contributes to shell strength will allow for selection of genetic traits in laying hens to produce consistently stronger eggs for enhanced food safety.”5
The evolutionary wink and nod
Despite the rather obvious design features of the chicken egg, and the potential applications of copying some of these, the researchers paid the usual homage to blind evolution. McKee said: “When you think about it, we should be making materials that are inspired by nature and by biology because, boy, it is really hard to beat hundreds of millions of years of evolution in perfecting something.”7 Yet the paper never even hinted at explaining how such a wonderful biomineralized life-supporting chamber could actually arise through hundreds of millions of years of a bit-by-bit evolutionary process. Like the waving of a magic wand, it’s as if just writing the words makes it so!
But there are many difficulties in this idea of the egg being perfected by selection of random changes over millions of years. Achieving this rather complicated balance of structural and mechanical properties needs to happen in different ways at different times of development. If the shell were not sufficiently strong outside, then it would not protect the chick. If it did not dissolve inside, then there would not be enough calcium for the bones to form, nor would the chick be able to break through and hatch. And if the thinning of the shell happened too soon, then it would compromise its protective function. How did the ancestors of today’s chickens reproduce for millions of years before that process was allegedly perfected to the point of ensuring the next generation of birds?
The research discussed here only scratches the surface of the many mechanisms involved in egg design and function, including other proteins, which are still poorly understood. The credit for this ‘eggcellent’ design8 does not belong to evolution, but rather to the One who is “worthy … to receive glory and honor and power, for you created all things, and by your will they existed and were created” (Revelation 4:11).
To demonstrate how the osteopontin (OPN) affected nanostructure in synthetic calcium carbonate, calcite crystals were grown in its presence. Pictures A, B and C show no, low and high concentrations of osteopontin added to the synthetic calcium carbonate respectively. Notably, the measured nanostructure size from the synthetic calcite grown at the low osteopontin concentration was similar to the size found in the inner region of the eggshell, whereas the higher osteopontin concentration produced a nanostructure size similar to the outer part of the eggshell.
References and notes
- Fabry, M., Now you know: which came first, the chicken or the egg?, time.com, 21 September 2016. Return to text.
- Attenborough, D., Attenborough’s Wonder of Eggs, screened on BBC 2, 31 March 2018. Return to text.
- Science Buddies, Porous science: How does a developing chick breathe inside its egg shell? scientificamerican.com, 3 May 2012. Return to text.
- Athanasiadou, D., and 14 others, Nanostructure, osteopontin, and mechanical properties of calcitic avian eggshell, Science Advances 4(3) eaar3219, 2018 | doi: 10.1126/sciadv.aar3219. Return to text.
- McGill University, Cracking eggshell nanostructure: New discovery could have important implications for food safety, phys.org, 30 March 2018. Return to text.
- Chien, Y.C., and 3 others, Ultrastructural matrix-mineral relationships in avian eggshell, and effects of osteopontin on calcite growth in vitro, J. Structural Biology, 163(1):84–99, 2008 | doi: 10.1016/j.jsb.2008.04.008. Return to text.
- Davis, N., Scientists solve eggshell mystery of how chicks hatch, theguardian.com, 30 March 2018. Return to text.
- Catchpoole, D., What’s in an Egg? Unscrambling the mysteries, Creation 24(3):41–43, 2002; creation.com/egg. Return to text.