Robin Hanson and Bryan Caplan were having an argument about something called “Em.” I have no idea what Em is so I am not writing about that. But the argument had something to do with slavery, and it prompted Hanson to do a quick review of the literature and write up a summary on his blog overcoming bias. I’m afraid that Hanson’s quick review of the literature was a bit too quick. Some of the statements are simply wrong and others can reasonably be contested. I posted these responses on his blog, but it did not seem to keep the links. Consequently, I'm posting it here as well.
He states that
Historically, even when slaves were common, they were usually a minority of the population. (Beware, the term “slave” is used in different ways.) About 10% in the Roman Empire and US south.
This statement is simply incorrect. Slaves accounted for substantially more than 10 percent of the population of the South. Slaves were as much as 57 percent of the population (South Caroline) and at least 25 percent (Tennessee). See, for instance, Jenny Wahl. Or you can check at the Historical Census Browser at UVA
He states that
(The sex story is overrated, as only 1-2% of slave babies were fathered by white men.)
The first thing to note is that, unlike population, the number of children born to slave mothers and white fathers is difficult to estimate. Some estimates put it as low as 1-2 percent, but Stephen Crawford found that in ex-slave interviews, by the WPA and Fisk University, as many 10 percent of slaves reported that their father was white. The 10 percent figure was when the interviews were done by African –American interviewers. In other words we don’t know. It may be possible use genetic studies to produce a more accurate estimate, but I don’t know of such a study. There is also the question of “How large is large?” Stating that “the sex story is overrated” suggests that 1-2 percent is somehow not important. Given that the vast majority of enslaved people in the South lived on plantations of 15 or more people, even 1 or 2 percent could be consistent with a relatively large percentage of slave owners fathering an enslaved child (or a smaller percentage fathering numerous children). It is not obvious to me that 1 or 2 percent is small in this case.
He states that
Sometimes people sold themselves into slavery for a limited time, as with indentured servitude.
This is just kind of odd. It may be that he is using a definition of slavery that makes this make sense, but I don’t know of any historian who regards slavery and indentured servitude as equivalent.
Finally, he states that
Slaves weren’t converted into debt perhaps because of credit market failures, or more plausible because the full control approach was especially productive on plantations.
I’m not entirely clear about what this means, but it does not sound consistent with current understanding of slavery in the United States. Historians have devoted considerable attention to the well developed credit markets that facilitated slave purchases. See for instance, recent work by Bonnie Martin, John Clegg, Calvin Schemerhorn, Kathryn Boodry, and Gonzalez, Marshall, and Naidu.