Preface
Gil Scott-Heron, Winter In America, Central Park Summerstage, NYC 6-27-10 (HD).
This come from an old African folk tale. I know this because it was
told to me by some old Africans. You got to be careful where you get
your information. See you can't get no old African folk tales from no
young Chinese people.
We know that englishmen in the colonies and what would become the "United States" forced prisoners of war (what englishmen refer to as "slaves") to have sexual intercourse with their mothers, in an effort to produce more prisoners of war, for free labor, fun, glory, material gain, and experimentation, see Medical Apartheid
The Dark History of Medical Experimentation on Black Americans from Colonial Times to the Present by Harriet A. Washington. Forcing young prisoners of war to impregnate their mothers is but one of the horrendous practices of englishmen in the western hemisphere. Without such experiments what is referred to "modern medicine" would not exist. If you find the time, browse the historical medical records of the University of Chicago.
That is the origin of the term motherfucker from which the cheaper by the dozen phrase was used to refer to the offspring of such forced impregnation.
The late Dick Gregory revealed many of these historical facts before their passing. It has been some time since last reviewed the actual phrases usage. Am not entirely certain if Dick Gregory is the one and only source of the meaning of that phrase, within the context of the offspring of male prisoners of war in the western hemisphere being forced to impregnate their mothers to produce more prisoners of war.
It is not surprising that anglophiles deny, or refute such origins of terms in the english language.
Though for an individual who is not an englophile, it is common knowledge that english is first and foremost an equivocal language, intended to be used for deception, capable of having more than one meaning for each word or phrase. There is no such thing as "good" or "proper" english. The language is a result of conquest by the Normans, Romans, whores, convicts, pimps, murderers, imperialism and several hundred years of institutional white supremacy.
In any event, this Dick Gregory - On Slavery, Reparations and Hurricanes
... we can't have no more. How we gonna do this?... So he made me, 14
years old, put a sock over my head, and have sex, fuck my mama...
...cause she didn't want him to get made and start killing the
slaves...
... and so, I had to screw my mama man...
... That's where the word motherfucker comes from and then white
boys shit and they hated the word until they got around black folks...
... and now you go to a white movie and they say mothafucka before
they finish running the credits from the movie...
is a brief introduction to the emergence of the phrase "cheaper by the dozen" being used to refer to the offspring of so-called "black" or african women in the western hemisphere being force to be impregnated by their sons, the result of which was often birth defects, which were still valuable "property" for those englishmen who bought and sold human beings. The interview provides accounts for the origin of the terms honky and motherfucker. Will edit the answer to address specifically how the motherfucker history resulted in cheaper by the dozen.
Note, that same interview describes the origin of the term honky, which is derived from english, or so-called "white" men literally honking the horn of their vehicle outside of the whorehouse they were visiting to buy sex from so-called "black" women.
The History Of Male Slave Rape (Buck Breaking) And The Word MotherFucker (which are excerpts from the documentary Hidden Colors)
...especially in Jamaica, they were doing a process called "buck
breaking" where the white supremacist slave owner or the white
supremacist overseer would literally rape black men in front of the
black population in order to break his spirit, in order to break him
down as a man, in order to show dominance against him, in order to
show the rest of the black population that this is not your leader I
just made your leader submit to me sexually. -Tariq Nasheed, Lecturer/Producer
It was a matter of power and control and domination, and they would
call it "buck busting" but it was really "butt busting".-Dr. Patricia Newton, Psychiatrist
Slavery continued until 1865... for about two generations, right, so
how do you reconcile that?
You can no longer bring in Africans but you still have the business of
slavery, so they still needed Africans to do the work down south,
especially after the cotton gin was invented.
So you had the creation of breeding farms. Two of the largest slave
breeding farms in the United States were on the eastern shore of
Maryland, and right outside or Richmond, Virginia. The literally bred
black people like cattle.
They would have a strong black man have sex with a healthy black
woman.That woman could be his mother, his sister, his aunt, his
cousin. It didn't matter. Because the end product was product a child
that I can sell, bodies that I could sell and ship down to
Mississippi, Alabama, Georgia, South Carolina, North Carolina. It was
a business. -Anthony T. Browder
We had breeding farms in the United States... Even if you were mother
and son, they would mate you... And so I tell a lot of my patients
and a lot of my friends, you gotta stop using the "MF" word because
that was a description of what actually happened when they would put
the paper bag would go over the head to put one breeder against
another when they were related. -Dr. Patricia Newton, Psychiatrist
The Origins of The Dirty Dozens
The term the dozens is believed to refer to the devaluing on the
auction block of slaves who were past their prime, who were deformed,
aged or who, after years of back-breaking toil, no longer were capable
of hard labor. These enslaved human beings often were sold by the
dozen. In African American Oral Traditions in Louisiana, African
American author and professor Mona Lisa Saloy writes: “The dozens has
its origins in the slave trade of New Orleans where deformed
slaves—generally slaves punished with dismemberment for
disobedience—were grouped in lots of a 'cheap dozen' for sale to slave
owners. For a Black to be sold as part of the 'dozens' was the lowest
blow possible.”
African American Oral Traditions in Louisiana By Mona Lisa Saloy, author, folklorist, essayist, poet, professor of English at Dillard University
"The Dozens" are an elaborate insult contest. Rather than insulting an
opponent directly, a contestant derides members of the opponent's
family, usually his mother. The dozens has its origins in the slave
trade of New Orleans where deformed slaves—generally slaves punished
with dismemberment for disobedience—were grouped in lots of a "cheap
dozen" for sale to slave owners. For a Black to be sold as part of the
"dozens" was the lowest blow possible.