The Biology of Slavery

Why did slavery pay?  In what circumstances?  In a Malthusian world, a laborer’s pay is just enough to allow him to raise two kids to adulthood. That’s all the average peasant makes, so that’s all an employer has to pay.  Someone who raised slaves for labor would have to spend just as much or go out of business, in the long run.

So, in the  Classical world, slaves mainly made economic sense (for the masters, natch) only if you could steal them, generally through wars of conquest. If Rome enslaved a 20-year Thracian farmer, they could get decades of work out of him without having to pay for his upbringing. All of this assumes that the Romans  had special expertise in conquest and social control, and for the most part they did.  Of course,  if they picked the wrong Thracian, they could be sorry.

As the Roman Empire cut back on conquest, slaves cost more.  Since the Empire had a fairly long period of internal peace and good government,  living standards naturally dropped. Population growth far outpaced technical innovation, which was never a Roman strong point.  Slavery seems to have become less and less important.  Certainly there was no long-term, self-sustaining population of slaves.

Slavery in the American colonial era is a very different story.  Although many slaves were imported from Africa,  the slave population  reproduced quite successfully.  As C. Vann Woodward wrote: “So far as history reveals, no other slave society, whether of antiquity or modern times, has so much as sustained, much less greatly multiplied, its slave population by relying on natural increase.” In a mostly-Malthusian world,  that is exactly what you would expect.

Before the War of the Rebellion, the natural growth of the slave population was about 25% per decade, greater than any country in Europe.   That doesn’t necessarily mean that the slave health and nutrition was equivalent to that of white Americans, or that their lives were easy: but they had a higher standard of living than the typical peasant in a country with a stable population.   The  main underlying reason was that the US, in those days, was one of the least Malthusian place that has ever existed.  The Amerindian population had collapsed (not before transmitting highly productive crops such as maize) and land was abundant.  Food was abundant and labor was not.

You can see why slavery might pay, but why African slavery?   There is reason to think that they were more productive farm workers than Europeans in the American South , largely because they  were significantly more resistant to a number of tropical diseases. Almost all people from central and west Africa are Duffy negative and are highly resistant to vivax malaria. A number of different mutations common in those same populations, such as sickle-cell, Hemoglobin C, G6PD deficiency,etc. etc.  give substantial protection against falciparum malaria.  Although the genetic details are at this point not understood, people  from sub-Saharan Africa are also resistant to hookworm and are more likely to survive yellow fever.    One would suspect that they also have greater heat tolerance.

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38 Responses to The Biology of Slavery

  1. dearieme says:

    “largely because they were significantly more resistant to a number of tropical diseases”: mm, but weren’t a lot of those disease imported when the slaves were brought in? Still, perhaps that means that once you had brought in lots of African slaves there was an added incentive to bring in more. Is there a name for that sort of ‘trap’?

  2. Ben Atlas says:

    Hi Gregory, your view of the population growth of the american slaves is a bit simplistic. Out of all people Karl Marx had a sober view of the American slavery and he makes the distinction between ‘slave producing’ and ‘slave using’ states in his notes about the Civil War. I posted that quote on my blog a while ago:

    So you can see that the growth was rather intentional to fuel the territorial expansion, a rather unique cluster of events. I don’t know if at any other point in history the salves were literally bread to be slaves. Perhaps the usual suspects, the Inca empire, Egypt, ahem, CCCP. etc.

    • gcochran9 says:

      This is probably going to shock you, but Karl Marx was wrong. Nobody can be right ALL of the time. Slaves had positive population growth almost everywhere in the American South. The main exception seems to have been sugar cane plantations.

      • Ben Atlas says:

        Gregory, I spend a lifetime undoing my previous assumptions, these things don’t shock me, they excite me. But even if there was the growth everywhere perhaps the growth was the “salve” business in some state.

        • saintonge235 says:

          In the decades before the war, the older slave states exported slaves to the Southwest states such as Mississippi and Arkansas. Those states had a lot of never-cultivated land. Cheap, abundant land with a long growing season, but acidic soil–it shaped the Southern economics big time.

          As for the classic world, slave owners were advised to deliberately work their property to death over a decade or so. Constant, low-level starvation discouraged revolt. Stalin would have approved.

  3. Sean says:

    I don’t know how common it was to cultivate malarial areas, I have read the owners avoided exposing slaves to danger as they took a loss if anything happened to their property, and that Irishmen were hired for dangerous work. Many of the early slaves in Virginia were white, but a white child born to a white slave mother was not a slave. A black child born to a slave or indentured mother (black or white) was, and the women were often were given no choice about who impregnated them. So there was an economic motive for preferring slaves of African ancestry.

    • gcochran9 says:

      Sean, what universe are you from? Vivax malaria existed in most of the South, falciparum in the lower tier. And there were, of course, no white slaves in the British colonies. Indentured servants, sure.

      • Sean says:

        Whites suffered badly from hookworm in the West Indies. I wonder if the ‘difficult’ male slaves got many opportunities to reproduce. Maybe ‘natural increase’ was included selective breeding for characteristics the slaveholders valued.

      • Well, no white slaves aside from a few prisoners shipped there as special punishment. In the novel Captain Blood, the protagonist is among them. The fifteen-pound asking price for one of his group is contemptuously rejected with “I can get a Negro for that. These white swine don’t live. They’re not fit for the labour.” It is fiction, of course, but the setting is real enough.

      • Frank says:

        >”there were, of course, no white slaves in the British colonies. Indentured servants, sure.”

        Not quite. Indentured servants were people who voluntarily sold their labor for a set period of time in exchange for transportation to the “New World”. But there were plenty of white slaves as well, people sent to work in the West Indies until they died. There is even a word for this – “Barbadosed”, which comes from Oliver Cromwell’s habit of deporting defeated rebels from the English Civil War – mostly Irishmen – to Caribbean Islands, mainly Barbados. Their status was not that of indentured servants.

    • Misdreavus says:

      It would truly be delightful if people as obnoxiously stupid as this abstained from commenting on this blog.

      Sean rarely (if ever) has anything of worth to contribute to any conversation, and somebody needs to drive the point to him loud and clear.

      • Sean says:

        The post was about slave-based operations. I knew about malaria ( see comment link below). But, malarial land in the south sounds like it would be undesirable and farmed by poor whites. Would slaveholders have risked their valuable ‘property’ trying to farm those areas? There does not seem to have been selection for resistance to malaria Jin et al. (2011) ” Further analysis showed that the frequencies of alleles protecting against malaria in AAF were lower than those in IAF, which is consistent with the relaxed selection pressure of malaria in the New World. ”
        17 January, 2012 . Apart from the indentured status, there were white slaves in Virginia.

        • gcochran9 says:

          Sean, malarial land was the best land, economically. The lowlands had better soil and better access to sea transportation. The ideal tobacco plantation in Virginia was on a lowland river. Nobody cared about roads.

          I don’t think that Virginia had falciparum, which was far deadlier than vivax. At least not often. And even in those places that had falciparum, like South Carolina, it likely wasn’t as common as in West Africa. So slaves had reduced selection for malaria defenses, and the gene frequency of sickle-cell probably dropped with time, particularly outside the lower South.

          Still, differences in disease resistance were important enough that blacks did noticeably better demographically than whites in South Carolina, just as blacks did noticeably worse than whites in New England.

          • saintonge235 says:

            The slave owners did notice that malaria was seasonal in the New World, and frequently went on very extended vacations during the dangerous summer months. But malaria still happened to whites. Jeff Davis lost his first wife to malaria.

    • Dave says:

      Sean, there’s a recent book ‘1493’ which goes into all of this. Whites died hugely in the first and later stages of settling Virginia + other parts of the South, because of malaria. Africans were resistant.

  4. Gene Berman says:

    Dr. Cochran:

    You’re certainly “cutting edge” in some fields but, in this one, you seem “stuck” back in the 19th century–a point from which nearly all economic science has “moved on.”

    Let me bring you (and Ben Atlas, seemingly frozen in time–like “the ice-man”) a little closer to modern times (and reality).

    The tendency for workers to be paid just that amount that would enable them to subsist and to reproduce is not “Malthusian,” though it seems to smack of a gloominess that’s come down to us in that association. What youve put forward is “The Iron Law of Wages.” (Ricardo–which became an underpinning of “classical” economists, i.e., Ricardians) and, pretty much, “holy writ” until dis-placed entirely by a far more realistic understanding–the “subjective theory of value” to which virtually all modern economists subscribe (except Marxists and Georgists). The newer recognition occurred just about 1870 to three economic thinkers, entirely independent of one another: an Englishman (Jevons), a Swiss (Walras), and an Austrian (Menger). The last-named also made a series of further logical deductions from the original premise, forming the basis (and also the method) for what is known today as the “Austrian School.”

    For Ben Atlas: at the time that the (above-referenced) discovery was being made, the first volume of “Das Kapital” had been published and a second and third were supposedly in the works. Though I do not know such a thing as fact, it is my surmise that the length of time until Vols II and III were published were necessitated by Marx’ (and Engels’) recognition of the irrefutable character of subjective value theory and an effort to remove (and, perhaps, rewrite) all those portions which could cause them polemic problems under the newer, more powerful light. When one comes right down to it, subjective value and marginal utility theory devastate nearly everything Marx had ever had to say. That being said, there’s no doubt whatever in my mind that Marx’s writing is the most powerful that has ever existed; his knack was to expand and theorize upon that which many or most already tend to believe: I’d call most adults in the world today Marxists to one degree or another.

    Back to slavery. I’m going to suggest, Dr. Cochran, that you read Ludwig von Mises’ section on slavery in HUMAN ACTION; it’s just a bit more than 6 pages (and I think you’d be able to find it downloadable thru the websirte). One curious thing. In the mid-’50s, in school, I was asked to write two papers (@ $100 each–a pricely sum in those days, when few made $100 in a week). One was to be on Marxian economic theory and the other was to be on “Economics of the Pre-Civil War South and the Confederate States of America” (for different students). I did it as a job–I had no interest at that time in economic topics of any kind–merely “skimmed” both books

    But I never forgot what I read about the southern economy. Apparently, nearly every plantation of any size was deeply in debt: 3 or 4 years’ earnings was a typical mortgage. Such loans were only possible because the slave “livestock” was valued at market–many of the lenders were northern banks (the modern theory of value would have dissuaded many of these from making such loans). Much was made in the way of propaganda (in the North and overseas) of the fact that every one of the CSA political leaders was heavily indebted (and mainly to northern banks)–the implication being that seccession had been urged so these leaders could renege on their indebtedness.

  5. dave chamberlin says:

    For further detail I have to put in a plug for a great book “1493” by Thomas Mann. In this book you find out the Mason Dixon line wasn’t put there by accident, it just happens to be the northern boundry beyond which the mosquito that carried the worst form of malaria, falciparum, did not thrive. There is a lot of history that makes better sense when the importance of disease and disease resistance are given their rightful place. Perhaps I can prod Greg Cochran to write up a future thread on the impact of malaria on the Roman Empire, to give one example.

    • dave chamberlin says:

      I meant Charles Mann

    • gcochran9 says:

      Having read 1491, I would probably not bother to read anything else by Mann. He’s not all that reliable.

      • FredR says:

        pls xpnd

      • dave chamberlin says:

        I thought 1491 and 1493 were great books BUT 1491 got more than a little carried away with PC nonsense. We are damned different but Mann says the amerinds just got the short end of the stick regarding disease resistance and that’s the whole story. It is not. Mann makes some enthusiastic estimates of North and South American populations at the time of 1491. There were large parts of North America thinly populated by amerinds in 1491 because the hard work of farming bored them while attacking the nieghbors beserker Viking style just never got old. I could go on at length about the shenanigans of those “noble savages” as reported by the first explorers but suprisingly the history books post 1970 or so leave out all the accounts of torture and cannabalism as a means to get your nieghboring tribe to move a bit farther away.

  6. dearieme says:

    “Many of the early slaves in Virginia were white”: really? Not indentured labour or convict labour, actual slaves?

  7. Ben Atlas says:

    To.Gene Berman, thank you for the interesting references although I fail to understand how a quote from Karl Marx, when he worked as journalist, represents his economics theories or the competing economic theories at the time. It was just the reference to the reproductive rate of american slaves and the historical context.

  8. brucecharlton says:

    25 percent increase per decade… phew!

    Yes that must mean what you say it means – that US slaves were significantly better off than European peasants.

    If Greg Clark’s data for England is generalizable then the Peasants had a reproductive success of *less* than two children and the societies were continually repopulated by downward mobility from the middle classes. So the margin of prosperity between US slaves and Euro peasants was even greater than the above.


    The other really big and longer lasting slaving society – North Africa/ Arabia – kidnapped its (?) millions of mostly white slaves, used them as motors in galleys until they died, marched them across the Sahara and worked them to death leaving not a genetic wrack behind (or did the sex slaves in the harems perhaps leave a genetic trace?) – indeed barely any records of any kind. Therefore the whole episode is unknown/ forgotten.


    One aspect of slavery you didn’t mention is sex slavery. Female mulattoes commanded the highest prices of all slaves in the American South, more than economic workers (strong young men field hands etc).

    I have always suspected that the (mostly female) abolition movement in in the North East US was mostly fueled by disgust at female sex slavery (the implied fate of Topsy perhaps?), rather than the plight of male field hands.

  9. Steve Sailer says:

    Also, tobacco farming in Virginia and North Carolina was pretty non-lethal work compared to sugar cane farming in Brazil, with cotton farming in the Deep South in between.

  10. j says:

    Regarding the biology of slavery, it would be interesting to read about the genetic impact of slavery on the slave population and on the slaver population. The Atlantic passage and 200 years of slavery must be reflected on that population, and the gene flow must have been mutual.
    Other nations with massive slave experience are the Caribbean islands of Haiti, Jamaica, Cuba; Brasil, and Oman & Saudi Arabia. Looking at the Ibn Saud family pictures, one may say that African and West Asian slaves merged with the local populations in the Arabian peninsula. It is interesting to observe that Africans were imported into the Turkish Empire in the 19th CEntury to cultivate malarial areas on the Mediterranean coast from Egypt to Greece. I think mostly they mixed with local populations and one can find African genes in all Mediterranean coast populations (Dienekes will disagree regarding Greeks). In Israel we have African descendant villages such as Djisser El Zarka that are completely African. Not like the Saudis, Palestinians did not marry them and during Israel’s war of independence and successive uprisings they always sided with us.

    • Mark says:

      Jews have a long relationship with Africa and Africans as slavers, slave traders, traders, etc. and there is evidence suggesting that it has left a genetic impact:

      In 2011, Moorjani[54] et al. show to have detected 3%–5% sub-Saharan African ancestry in all eight of the diverse Jewish populations (Ashkenazim, Syrian Jews, Iranian Jews, Iraqi Jews, Greek Jews, Turkey Jews, Italian Jews) that they analyzed. Researchers from the Harvard Medical School estimate that the exchange of genes occurred approximately 72 generations ago (or about 2,000 years). Lawrence Schiffman, professor of Hebrew and Judaic studies at Yeshiva University, believes the intermixing may have occurred during the Hellenistic period (c. 320–30 B.C.E.), when Jewish communities were resident in many North African coastal cities, or during the First Temple period (c. 950–600 B.C.E.), when the Israelite kings, including Solomon,
      had trade relationships with Africa.[55]

    • Mark says:

      Jews have a long relationship with Africa and Africans as slavers, slave traders, traders, etc and there is evidence suggesting that it has left a genetic impact:

      In 2011, Moorjani[54] et al. show to have detected 3%–5% sub-Saharan African ancestry in all eight of the diverse Jewish populations (Ashkenazim, Syrian Jews, Iranian Jews, Iraqi Jews, Greek Jews, Turkey Jews, Italian Jews) that they analyzed. Researchers from the Harvard Medical School estimate that the exchange of genes occurred approximately 72 generations ago (or about 2,000 years). Lawrence Schiffman, professor of Hebrew and Judaic studies at Yeshiva University, believes the intermixing may have occurred during the Hellenistic period (c. 320–30 B.C.E.), when Jewish communities were resident in many North African coastal cities, or during the First Temple period (c. 950–600 B.C.E.), when the Israelite kings, including Solomon,
      had trade relationships with Africa.[55]

  11. Luke Lea says:

    My understanding is that slaves were generally worked to death on the sugar islands, to be replaced by fresh imports from Africa. They did not reproduce the way they did in America.

  12. thrasymachus33308 says:

    I had an economics class- I forget the title- and the main book was “Time on the Cross”. Slaves actually had a higher “income” in terms of food and other benefits, but were far more productive.

    I read in some Civil War magazine that hookworm was widespread in the South and not really controlled until around the 1930’s, with significant effect on the poor white population.

  13. iberian says:

    Brucecharlton – Muslims and Christians are not diferent races… the mix of a French with a Algerian is similar to both; a vulgar caucasian , more or less light or dark… It´s why you think that europeans don´t let an signal in north-africa or midle east. The influence of Negro´s it´s obvious in north-africa (and some parts of midle-east) because they belong to really a distinct racial stock. But, don´t worry, they a let big “signal”; I see more blue eyes in Istambul than in Rome and not much time ago, I met one big guy, blonde, bue eyes, pink skin, that I take for Russian or German; after all, was a Syrian from Aleppo…He said that is common there…

  14. teageegeepea says:

    Evsey Domar theorized that it makes sense to institute slavery rather than peasantry when you have a surplus of land and a shortage of labor. Russia gained a lot of land when they defeated steppe nomads with modern weapons, hence serfdom in the 16th century.

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  17. Dale says:

    It seems likely that West Africans were particularly suitable for heavy hand labor in fields. West Africa was a center of “hoe agriculture”, where crops are tended not with plows but hoes. Which seems to make it possible to use women and children for farm work, but puts them under selection for physical strength. And apparently, West Africans are the burliest people in the world, which would make it a good place for a slaver to buy his goods if he was delivering them to tobacco, cotton, and sugar cane fields. (And leading to the predominance of American Blacks in basketball and football.)

    But once importing slaves was banned in 1808, the best way for a US slave holder to make money was to breed slaves as fast as possible. It seems that at most 600,000 slaves were imported into the US (far fewer than into the Caribbean), generating a current population of about 40 million (30 million Africans, by blood-fraction). That’s a growth factor of at least 67, which is Pretty Damned Good for any human population.

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