This is just a placeholder answer while look for the complete connection to the phrase "cheaper by the dozen".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.
...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 fron toffront 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.
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