As we crack open our boiled egg on Sunday morning we may forget that the egg was meant, in the first place, to be the home of a baby chicken. Inside that smooth shell was a com­plete food supply and life-support system. In three weeks it would take an embryo all the way from its first living cell, formed by fusion of the sperm from the cockerel with the ovum of the hen, right through to hatching as a run-about, cheeping chick. Mammal embryos develop inside the mother’s body. They do not need a separate food supply, because they receive nutrients from the blood stream of the mother. Similarly, they obtain oxygen from her lungs via the placenta (part of the womb lining), and excrete carbon dioxide in the same way. With birds it is different. The whole period of develop­ment takes place outside the mother’s body. The egg has to start off with a package inside the shell of everything the embryo will need during those twenty one days – food supply, breathing equip­ment, protection from shock and hostile bacteria, etc. It can be likened to the capsule on the end of a space rocket, which also has to contain everything needed to support the astronauts for the duration of their mission. Once the rocket has launched, it is not possible to go back for something that has been forgotten.

Egg Layers

Once you begin to examine the contents of an egg, you are impressed with the business-like way in which all the requirements for survival have been met. Let us take some examples. During its develop­ment, the embryo has to create muscles, skin, nerves, blood and feathers. The nutrients needed for this purpose must all be enclosed in the shell. Muscles, for example, are made up of proteins, which in turn are built up from amino acids. Fourteen amino acids are essential for a chicken (others it can synthesize [build up] for itself). All fourteen are present in the white of the egg. Fat-soluble vitamins such as Vitamin A and D are found in the yolk of the egg, and B vitamins in the white. A major requirement during development will be the calcium and phosphorus needed to make the bones of the skeleton. There is a perfect source ready to hand in the shell of the egg, which is a mixture of calcium and phos­phorus salts. This vital nutrient is absorbed into the blood stream via a membrane which comes to lie just under the shell.

The astronauts in their capsule have to be safely strapped down in harnesses to protect them from vibration and buffeting during take-off and landing. The chicken embryo is also safely sus­pended in the centre of the egg, attached to the yolk, and surrounded by rubbery egg white. A neat cradle of protein strings, anchored firmly into the ends of the egg, surrounds the yolk like a football in a net, to ensure the yolk is free to rotate if the egg is disturbed. The spot on the yolk where the embryo grows is less dense than the rest, so the yolk rotates in its cradle until the embryo is uppermost, next to the warmth of the mother hen sitting on her nest. Next time you break an egg into the frying pan, look out for the remains of these strings – curly white bundles next to the yolk.

Egg Shell

How does the embryo breathe? During the early days very little oxygen is needed. As the chick grows, a balloon-like membrane spreads out from the navel which is rich in arteries and veins. This eventually surrounds the baby chick on all sides, and comes to lie next to the shell. The smooth shell of a hen’s egg is made from tiny granules of calcium carbon­ate (chalk). However, viewed under a microscope it can be seen to be penetrated by thousands of tiny pores which are lightly plugged with a waxy film. Oxygen is able to diffuse downwards through these pores and enter the veins in the membrane below, from where it is carried back to the heart. Similarly carbon dioxide can work its way outwards from the arteries to the shell membrane, leaving the embryo’s blood free from poisonous gas. The waxy layer keeps out hungry bacteria, for which the contents of the egg would be a perfect food supply. There is also an enzyme (a protein which speeds up chemical reactions) in the white of the egg, called lysozyme, which attacks and destroys any bacteria that do happen to penetrate the pores.

Egg Hatched

A most interesting question is how the embryo escapes from the egg at the end of the three weeks. When the American astronauts splashed down into the ocean, the capsule had a hatch on the outside. This was opened by navy frogmen who released them and hustled them away in inflatable dinghies. But the chick has no such outside help. How can it break through the tough, unyielding chalky wall that surrounds it? Think how hard you have to tap with your teaspoon before the shell begins to crack. The answer is that three days before hatching, the chick turns around in the shell so that its beak is pointing under its right shoulder towards the large end of the egg. This end is hollow, with a space in the outer membrane that encloses a fat bubble of air (you can see this if you tap your egg on the large, not the pointed end). The beak at this stage is quite rubbery, like the bridge of your nose. It would never penetrate the shell. However, in the last days a small, tough cap called the egg tooth develops on the tip of the beak. This falls off after the chick is a few days old. On the twentieth day, the muscles on the underside of the neck begin to contract spasmodi­cally, driving the beak through into the air space. Here it can take in oxygen from the air there, and the lungs begin to inflate. The chick can be heard cheeping inside the egg at this stage, even though the shell is unbroken. With renewed strength, the egg tooth is hammered against the inside of the shell until it is punctured, and a small crater ap­pears on the outside. Shuffling with its feet against the inside of the shell, and pecking away, the chick slowly cuts a trail around the egg, like taking off the end of a can with a can-opener. Eventually it thrusts off the large end altogether, and crawls out, to lie drying out in the warmth of the mother hen’s feathers. One last amazing fact. The yolk of the egg is made up of thousands of globules of oil, enclosed in a membranous bag. Oil is rich in energy. The embryo needs very little energy while it is enclosed in the egg – its mother provides it with warmth, and it does not have to use its muscles very much. After hatching, though, it needs lots of energy to run behind its mother to find food, and escape from predators. Well, just before hatching the whole yolk is drawn inside the abdomen through the navel, and the hole heals over. The newly hatched baby now has a built-in ‘petrol tank’, rich in energy, already in place to keep it going for at least three days!

A Planned Project

OK, it is time for those questions again! We made some comparisons between the egg and the space capsule on the moon rocket. Each has to provide a safe and comfortable environment for a long pe­riod where there is no access to the outside world. Each has to provide food, oxygen, protection, and a means of escape at the end of the journey. But the moon rocket was the culmination of years of research by the best brains in the world. President Kennedy vowed to put men on the moon, and mil­lions of dollars were spent to accomplish this target.

Separate teams were set up to design the space suits, the capsule walls, the propulsion rockets, the control systems, the food and waste disposal ar­rangements, the harnesses and seats. A Project Co­ordinator had the responsibility of chivvying along the teams, deciding on priorities, bringing in new scientists where there was a problem. There were many test firings, spread over several years, before the first men were allowed on a mission. After each one, the results were scrutinised, weaknesses noted and corrected, and adjustments made. Only when all the teams were satisfied with the reliability of their share of the project – medical, life support, propulsion, guidance, communications – was the go-ahead given for the first rocket to the moon.

But in the case of the chicken and the egg, there were no design teams, if evolution is true. Every small adjustment came about through trial and error. The problem with this idea, as we found with the Mamba snake and the Arum lily, is that there are too many things that need to be perfected at the same time. You could finally arrive at a perfect menu for the yolk and the white, adding every one of the 14 essential amino acids, after many earlier failures when just one was missing and the embryo died. But the embryo also needs oxygen. If the early versions of the shell were solid chalk, the embryo might have plenty of food, but it would suffocate. It is essential that those tiny pores are left through the thickness of the shell to allow diffusion of gases. Not only that, but there has to be an egg tooth clipped on to the end of the beak, needed only for hatching, otherwise the embryo will reach full term, but perish inside the unyielding shell, unable to escape. The probability of all these systems arriving at perfection together is unbelievably tiny. Common sense tells us that this sort of combination never arrives in the real world. It is much simpler to accept the statement in Genesis chapter one that:

“God created the great sea creatures and every living creature that moves, with which the waters swarm, according to their kinds, and every winged bird according to its kind. And God saw that it was good. And God blessed them, saying, “Be fruitful and multiply and fill the waters in the seas, and let birds multiply on the earth” (Gen 1:21,22).