I am studying the slavery in the Americas, and I was surprised when I read this line: The average number of children born to an early 19th century southern slave woman was 9.2--twice as many as in the West Indies. ( source: http://www.digitalhistory.uh.edu/disp_textbook.cfm?smtID=2&psid=3044) While this number may not be accurate and may have decreased, but it is true that the slave population in the USA increased despite of the ban on slave importation in the early 19th century. Excuse my stupidity and lack of knowledge, I assume that the slaves in the USA south had full knowledge that their children would likely live their whole life as slaves. They were also aware of the misery of life as living as slaves. There was even a case of Margaret Garner, who killed her daughter to ensure she did not live as a slave. Now I do realize that slave breeding happened in the South. However, I still do not understand why would slaves in the American South have so many children. Considering the utter misery of living as a slave and lack of manumission, I do not understand why slaves would have 9.2 children in average(if the number is correct). If the slaves knew their children would live their whole life as slaves, which was full of pain, and were also aware that the owners could easily separate the family, then why did slaves in the USA south had any children at first place? And why so many?
You are by no means stupid. The fact that you are intrigued by a stat and want to know the information and history behind it shows your intelligence. I hope my short answer may help. I believe the source listed below will prove to do a better job than I will here so please see them after reading my response.
The reason for so many slave women having children is that it was simply not up to them. They were not viewed as humans and so even their sexuality was not their own. Many masters would pair the strongest male and female slaves and force them to conceive a child so that the slaveholder would have even stronger slaves. This would make him more wealthy as it gave him the strongest and most profitable slaves to work in his fields but also sell at auctions. As disgusting as this is it is largely believed to be true as many slave narratives recite it in detail.^1
Another reason for slave pregnancy was that rape of female slaves by their owners was also prevalent. "Slave women were forced to comply with sexual advances by their masters on a very regular basis."^2 So basically masters made young, single slaves the objects of their sexual pursuits.^3 If these rapes lead to pregnancies, this would have added to the number of children a female slave had in her lifetime.
The main reason for the forced pregnancies of many slave women? It was an economic advantage for the master, who multiplied his labor force through slave pregnancy. The more slaves the owner had, the wealthier he was. Therefore he would force his female slaves to become pregnant either by him or another slave. This is why, as you pointed out, you see so many slave births. The average slave woman gave birth for the first time at 19 years of age and had another child every 2 1/2 years.^4
[1] "On Slaveholder's Sexual Abuse of Slaves" pg. 2; http://nationalhumanitiescenter.org/pds/maai/enslavement/text6/masterslavesexualabuse.pdf This source may be most helpful to you as it gives primary source accounts of the sexual atrocities that faced slaves.
[2] Master-Slave Relations; http://www.bowdoin.edu/~prael/projects/gsonnen/page4.html
[3] PBS; "The Slave Experience: Men, Women, and Gender"; http://www.pbs.org/wnet/slavery/experience/gender/history2.html
[4] ibid.