Which came first, the chicken or the egg?
It was most definately the chicken!
Genesis 1:21: "And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good." KJV
It may have been the chicken that got here first, but it was the egg that was used for these winged fowl to go forth and multiply.
Each female chick starts life carrying the beginnings of thousands of undeveloped yolks inside her body, not all of which develope into eggs. A pullet (female chicken at birth) also starts life with two ovaries. As the pullet grows, the right ovary becomes undeveloped and only the left one becomes fully functionable. The functioning ovary contains all the undeveloped yolks the pullet was born with. In a pullet or nonlayer, all the yolks are small because none have developed in preparation for lay. However, in a hen (female chicken that has been in laying for at least 30 weeks) the yolks will range in size from the head of a pin to nearly full size. This cluster of yolks can be found along the backbone of the bird about halfway between her neck and tail. Below is a photo of a cluster of egg yolks found inside a hen.
When a pullet reaches laying age, one by one the yolks mature. The laying age of a pullet will range from 4 to 6 months depending on the breed. At any given time, the pullets body will contain yolks at various stages of developement. Approximately every 25 hours, a yolk is mature enough to be released into a the funnel of the oviduct. This process is called ovulation. Ovulation usually occurs about an hour after the previous egg was laid. Throughout its passage through the oviduct, the egg leads with its pointed end. While the egg progresses through the oviduct, it is constantly rotating within the spiral tube. This movement twists the structural fibers called the chalazae which form the rope-like strands that anchor the yolk in the thick egg white. Just before it is laid, the egg rotates so that the blunt end comes out first. The whole process takes about 25 hours. This causes a hen to lay about an hour later each day. A hens reproductive system slows down at night, thus she will eventually skip a day of lay altogether. It is then that a whole new multiple day laying cycle will begin the following morning. Below are two photos. One shows the anatomy as it is inside the hen and the other shows the anatomy laid out in real life form.
The egg is fertilized while in journey through the oviduct and just before reaching the shell gland or uterus. The sperm of the rooster (male chicken) is encased in various layers of egg white and wrapped in protective membranes. Once it reaches the shell gland, it is sealed within the shell. It is then enveloped in a fast drying fluid coating called the bloom or cuticle. In the photo below, this is referred to as the germinal disc.
When a rooster mates with a hen, the sperm travels quickly up the oviduct to fertilize a developing yolk. If the hen laid an egg shortly before, the mating will likely fertilize her next egg. The number of additional eggs that will be fertilized by one mating varies with the hens productivity and breed. Highly productive hens generally remain fertile longer than hens that lay at a slower rate. Single combed breeds remain fertile longer than rose combed breeds. The average duration of fertility is about 10 days. If a certain rooster is desired for mating, it is advisable to wait about 3 weeks after placing the desired cock with the hen to collect eggs for incubation. An egg must be fertilized by a rooster to hatch a chick.
Egg Shell Color:
Colored shells are the result of pigments added during shell formation. Out of the 25 hours most hens need to lay an egg, encasing each egg within a shell takes about 20 hours of that time. As a general rule, hens with white earlobes lay white eggs and hens with with red earlobes lay brown eggs. An exception to this rule would be the Crevecoeur, Dorking, Redcap, & Sumatra. These breeds all have red earlobes but lay white eggs. Araucana & Ameraucana breeds have red earlobes but lay blue eggs. Pendesenca, which have white earlobes, lay the darkest brown eggs of any breed. Poultry are broken into classes with the Asiatic & American class breeds laying brown eggs except for the Holland Breed. The Mediterranean class lay white eggs. All other classes will range from white, brown, tinted, blue and to the point of pinkish in color.
Brown Egg Layers:
Will produce eggs of varying shades ranging from barely tinted to nearly black. This is all thanks to a dozen different genes that influence shell color. Most of the pigment of a brown shell egg is deposited in the bloom, the last layer being added to the outside of the shell just before it is laid. When a brown shelled egg is broken, the inside of the shell will be paler than the outside or nearly white. Bloom disolves when wet and easily rubs off when dry. This explains why when cleaning a brown shell egg, some of the color is removed. In the Marans breed, the color can be removed by simply touching the egg right after it is laid. Stress can make brown shelled laying hens lay eggs that are lighter than usual color. This will vary from overcrowded nest, loud noises, & even the use of certain drugs such as cocccidiostats. As a brown egg layer ages, her eggs usually get paler. It is unknown exactly what causes this. One possibility is said to be that as the hen ages & her eggs get larger, the brown pigment bloom is spread over a larger surface area. This explanation however does not explain why the tapered end of the egg gets lighter than the rounded end.
Blue Egg Layers:
By contrast, the pigment of a blue shelled egg is deposited throughout the shell. It is therefore just as blue on the inside as it is on the outside. Green eggs result from crossing a blue egg layer with a brown egg layer. This gives you blue shelled eggs with a brown coating. The many different shades laid by so-called Easter egg chickens result from blue shells coated with different shades of brown bloom. Below are some photos of various colors of eggs laid by many different breeds of hens. Believe it or not, when it is all said and done, it is the rooster who carries the genetic for egg color. We gotta give some credit to the boys!