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Those chicken eggs they have for sale in the supermarket - where do they come from?
Chicken eggs come from female chickens, silly. Modern cultivars of "laying" chickens really lay it on. They lay many more eggs per year than their wild relatives, or their wild ancestors.
This trait is not the result of natural selection; it is the result of 1000's of years of human selection.
Where do eggs exit the chicken?
As they do from all birds, eggs exit the chicken from the chicken's cloaca. This is a multi-purpose orifice that is similar in shape, size, and function in both male and female chickens. In males, it is the exit point for sperm. In females, it is the entry point for sperm, and the exit point for eggs. In both sexes, it is the exit point for uric acid and feces - which plop out together.
However the eggs that are sold in the supermarket, the eggs of commerce, are generally unfertilized; they cannot ever develop into baby chicks.
To prevent fertilization, farmers isolate female egg-layers from males. The cloacal kiss, the process by which sperm leaves a male's cloaca, and enters a female's cloaca, is not part of an egg-layer's life. Occasionally some chicken sperm must get past chicken farm security, though no-one seems to know how, so all eggs are "candled" before being sold, to make sure the fertilized eggs do not get into the market place. Traditionally, candling meant transilluminating the egg, using the light from a candle. Today, very few actual candles are used in the process of candling chicken eggs.
Natural selection is the process whereby a trait which helps make an organism likely to survive long enough to reproduce, is inherited. The organism's environment selects - in a manner of speaking - organisms with that trait, for reproduction - sort of like the way humans select a trait, for reproduction. Organisms without the trait are more likely to die, before reproducing, than organisms with the trait. The difference between human selection and natural selection is that humans select things that humans want, while an organism's environment selects things that aid in survival of the organism.
For organisms being husbanded by humans and subjected to human selection, natural selection continues to work on them too. It results in organisms that have characteristics that aid in their survival and reproduction while under the care and supervision of humans. That is their environment: under the care and supervision of humans. The result is that such organisms will have characteristics that humans intended for them to have and are also likely to have characteristics that humans did not intend for them to have.
Did I ever tell you about the sex education that my children received at 6 years old, in first grade? I got a letter from the school saying "We would like to teach your child about sex. If you don't want us to, let us know, and we won't, otherwise we are going to teach your child about sex, understand? Check this box, if you understand, and have no objection, and return this form with your child. Otherwise check this other box and we'll take your child out of the classroom for awhile, and put him in the temporary classroom with the other uninformed kids."
Me: Bob, what did they tell you about sex?
Bob: Father puts sperm in mother, sperm goes into egg, egg grows in mother and becomes baby, baby comes out of mother.
Me: How does sperm get from the father to the mother?
Bob: The sperm goes in the uterus and goes to the falashian tube.
Me: Yes, fallopian tube, but how does the sperm get from the father to the mother?
Bob: The father puts it there.
Me: The father puts it there?
Bob: [silence. He seems bored now].
Me: Where does the father get it from, and how does he put it there?
Bob [puzzled look, and really really bored]:
Me: What is sperm?
Bob: [Puzzled look, and even more bored].
Me: How big is it?
Me: Where does he get it from?
Me: How does the father put it in the mother?
Bob: Puzzled look, puzzled look, puzzled look.
Me: Err, father puts his penis in the mother's vagina and sperm squirts out of his penis and goes into her vagina.
Bob: [flatly] No.
Me: Yes. It's called sexual intercourse, or...
Bob: [getting agitated] No. No! No.
Me: No? Why not?
Bob: [more agitated, almost crying] That's crazy. You're lying. You're crazy.
Me: They left some stuff out, your teachers. They told you what they wanted to tell you, what they thought you ought to know, but they didn't give you any real understanding of where babies come from, or what the involvement is, of mothers and fathers. They failed to educate you properly. Good thing you have a crazy father who tells things like they are. By the way, chickens make babies a little differently. Male chickens don't have a penis like male humans; they have a cloaca, just like a female chicken has, and the male chicken and female chicken put their cloacas up next to each other — it's called a "cloacal kiss." Then the sperm leaves the male cloaca and...
Bob: That makes more sense.