What’s in an Egg?
Posted on homepage: 2 January 2013 (GMT+10)
Unscrambling the mysteries
Imagine a container filled with amorphous-looking bits of metal, plastic and some software chips. Could you imagine it breaking out as a fully-assembled scale model motor car? Then growing larger as it absorbs raw materials, as well as energy, from its surroundings? What sort of advanced software engineering would be required? As for any ideas of it being able to ‘marry’ another like itself, thus repeating the whole cycle by producing another container of metal, plastic and software … such notions could rightly be dismissed as ludicrously far-fetched, even in our technologically advanced age. Yet in the world around us, similar things are happening all the time in those shell-wrapped marvels-in-miniature called eggs.
From egg to chicken
Chicken eggs are laid only about 25 hours after ovulation (i.e. release of the egg from the hen’s ovary). Breaking open the shell of a freshly-laid fertilized egg would reveal a tiny (2 mm, or 1/12 inch, in diameter) white mass of cells—the blastodisc—on top of the yolk.1 If an intact egg is kept warm under a broody hen or in an incubator, the chick will develop from these blastodisc cells, with body folds of the embryo beginning to separate from the underlying yolk.
Crucial to embryo development is the formation of various membranes (partitions) including the yolk sac, amnion and allantois. The amnion encloses the embryo inside a fluid-filled cavity which not only buffers the embryo against short-term external temperature extremes but also cushions it if the egg is bumped. With the embryo closed off from the outside world by the shell,2 there is the problem of how to dispose of excretory wastes. Here is where the allantois is so crucial, as it serves as the embryo’s garbage bag. (When the chick hatches, the accumulated wastes can be found sticking to the inside of the abandoned shell.)
While these membranes are forming, the embryo itself continues to develop, differentiating the various organ systems. Four days after an egg is laid, the heart is visible and large blood vessels can be seen to have grown out from the embryo into the yolk sac. By eight days the eyes, darkly pigmented, are prominent. On the 11th day the brain is visible through the transparent skull, the limbs are obviously developing, and feathers appear by the 14th day. By 21 days (i.e. just before hatching), the ‘egg tooth’ is visible—the knob on the end of the beak which the chick uses to break out of the shell.
- Eggs have long been hand-coloured and exchanged, apparently as part of the pre-Christian ‘rites of spring’.1 It is easy to see how the egg would be regarded as symbolic of the renewal of life after a long cold winter. In many cultures, the egg represented fertility and was a sacred symbol to the Babylonians.
- As Christianity spread, the egg was adopted by many as a symbol of Christ’s Resurrection. People in central European countries have a long tradition of making elaborately decorated Easter eggs. The Russian royal family carried this tradition to great lengths, as can be seen from the ornate jewelled eggs made by goldsmith Carl Fabergé from the 1880s until 1917.
- The Extraordinary Egg, <fairfield. osu.edu/fcs/openhearthapr23.html>, 25 February 2002.
Ready, set, grow!
Newly hatched chicks weighing around 40 g (1.4 oz) are now ready to find food for themselves. In favourable conditions they can grow extremely rapidly, attaining weights of 2.6 kg (5.7 lb) in around six weeks.3
All the instructions for a chicken this size were present in the original tiny blastodisc inside the egg. Could the egg, its contents of such intricate construction, wrapped in a seamless protective shell and programmed to grow, possibly have originated by evolutionary ‘chance and necessity’? The improbability of an egg, outside the context of a Creator God, simply defies reason (Romans 1:20).
Which came first? The chicken or the egg?
Evolutionists would reason as follows. A chicken comes only from a chicken egg. But in the past, they say, there must have been something almost like a chicken (but not quite) which gave rise to the first chicken, by mutation (random genetic copying mistakes). Given Mendel’s laws of inheritance, the transition from non-chicken to chicken can only take place between the egg-layer and the egg. Thus, they say, the egg came first.1,2
Let’s ignore here that their whole scheme relies on the belief that massive amounts of new information have to be added to convert a primordial fish into a chicken (no mutation has ever been observed that adds information to the DNA—just the opposite).3 What does the Bible say concerning the age-old question about the chicken and the egg?
According to Genesis 1, God created all the animals and birds, each ‘after their own kind’, and then instructed that they were to be fruitful, and multiply, and increase on the Earth.
So God designed and made the ‘chicken kind’ (male and female), and later, the very first ‘chicken egg’ was laid. To the extent that that first chicken population differed from today’s chickens, it would have been genetically richer, capable of giving rise to a wide variety within that particular kind. But the bottom line is that it was the chicken that came first, before its egg.
- The egg came before the chicken, <www.nyu.edu/gsas/dept/philo/faculty/sorensen/papers/egg.html>, 18 February 2002.
- Which came first, the chicken or the egg?, <www.howstuffworks. com/question85.htm>, 18 February 2002.
- Spetner, L., Not by chance!, The Judaica Press Inc., New York, pp. 138, 159–160, 1997.
What is an ‘egg’?
In biology, the term ‘egg’ most often refers to the female sex cell, or gamete, across a multitude of species, from rabbits to redwood trees, camels to corn plants.
However, ‘egg’ can also be used to describe the entire specialized structure or capsule that consists of the ovum, its various protective membranes, and any accompanying nutritive materials. Thus, for most people, an egg is a hard-shelled reproductive body (normally regarded as food) that is produced by a bird or reptile.
But it’s not just bird or turtle eggs that are considered as food. Fish eggs (‘roe’) are eagerly consumed by many around the world. In Russia, caviar—the salted eggs of sturgeonfish—is a prized delicacy.1
All birds, and some reptiles and fish, are oviparous—their eggs continue to develop after being laid, and hatch later. Some reptiles (e.g. Garter Snakes) and fish (e.g. guppies) are ovoviviparous—i.e. they have shelled eggs that hatch as they are laid, making it look like ‘live birth’. However (unlike the situation in viviparous organisms giving birth to live young—e.g. sheep), after ovulation, the mother’s body supplies no nutrients—only oxygen—to the developing embryo, which thus develops on the energy in the yolk.
- Encyclopedia Britannica, 15th Ed., 2:976, 4:386, 1992.
- If you hard-boil freshly-laid (still warm) eggs, the shell will stick to the white,
making it hard to peel. But as the egg mass shrinks from water loss after a few
days in the dry air of a refrigerator, the membrane separates from the hard shell,
allowing easy peeling.
Eggs harden when boiled due to the heat first breaking (unfolding) the proteins, which then allows these to form new, stronger bonds with other proteins. As these stronger cross-links form, the protein chains are prevented from sliding past each other, leaving the egg hard. Mechanical whisking of egg whites also breaks protein bonds, and again, new, stronger bonds subsequently form, so the material will never return to its original consistency.
- Blood spots in the egg are the result of rupture of one or more small blood vessels in the yolk at the time of ovulation.
- Double/triple yolks result when two/three ova are released from the ovary at the same time or when progress of the previous day’s ovum through the oviduct is slowed and the newer ovum catches up.
- Variation in internal colour is due to many factors. If very fresh, the egg white (albumen) will be cloudy, while a clear egg white is an indication the egg is aging. Pink or iridescent egg white indicates bacterial spoilage. The yellow shading of the yolk varies according to the hen’s diet—lighter on a colourless diet (e.g. white cornmeal) and dark yellow if she eats plenty of yellow-orange plant pigments called carotenoids (e.g. marigold petals and yellow corn). A green surface on the yolk is the result of overcooking, caused by sulfur compounds in the white reacting with iron compounds in the yolk.
- The colour of the eggshell depends largely on the breed of chicken. Chickens with white feathers, such as the Leghorn, White Rock and Cornish, lay white eggs. Dark-feathered (red-black) chickens such as the Rhode Island Red, New Hampshire and Plymouth Rock lay brown eggs. Araucuna chickens in South America lay eggs with shells ranging from medium blue to medium green.1
- The egg is laid blunt end first.
- Quail eggs have been successfully hatched in space (on the Russian Mir spacecraft in 1990 and 1992).2
- The extinct giant elephant bird (Aepyornis maximus) of Madagascar laid
eggs 39 cm (15.4 in) long with a volume of 12 litres (2.26 gal). Of living birds,
the ostrich egg is the largest, being up to 20 cm (8 in) long and weighing up to
1.76 kg (3.87 lb)—equivalent in volume to 24 chicken eggs. The smallest known
bird’s egg was a Vervain Hummingbird (Mellisuga minima) egg less than 9.9
mm (39/100 in) long, and weighing just 0.365 g (0.0128 oz).3,4
The largest dinosaur egg ever recovered (in China) was 46 cm (18 in) long.5,6
References and notes
- The Extraordinary Egg, <fairfield.osu.edu/fcs/openhearthapr23.html>, 25 February 2002.
- Incubator-Integrated Quail Experiments on Mir, <spaceflight.nasa.gov/history/shuttle-mir/science/fb/sc-fb-quail.htm>, 26 February 2002.
- Bird facts, <www.obelus.com/birds/facts.html>, 26 February 2002.
- The Amazing World of Birds, <www.earthlife.net/birds/intro.html>, 27 February 2002.
- Dinosaur eggs, <www.nationalgeographic.com/dinorama/eggs.html>, 27 February 2002.
- The animal pairs that God brought to Noah to put aboard the Ark would most likely
have been juveniles (perhaps timed to reach maturity at the end of the Flood—ready
to repopulate the Earth).
The relatively small size of dinosaur eggs shows that juveniles of even the largest dinosaur species were small enough to be easily accommodated in the Ark’s huge volume. See Grigg, R., Thunder lizards, Creation 22(4):14–17, 2000.
References and notes
- Information in this section is drawn from Curtis, H., Biology, 4th Ed., Worth Publishers, New York, pp. 859–864, 1983. Return to text.
- The shell stops the egg drying out but is porous enough to allow oxygen to filter in to the developing chick. It also protects the egg from most bacteria. A crack in the eggshell a few days after laying is usually fatal, as it allows bacteria to penetrate. A crack will also cause excessive moisture loss. Return to text.
- Agri Facts: Poultry and Egg Industry, <nfpc-cnpa.gc.ca/english/factpoultryeggstructure. html>, 26 February 2002. Return to text.