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Have crows avoided a Malthusian equilibrium?
Our greatest effect on crows is on their survivorship, not on their reproduction...if an adult crow lives near people it is likely to survive, but if it lives more than three miles from people, it will likely die. Mortality over a two-year period was 2.3 percent near people and 38.9 percent far from people...Populations in remote wildlands are not likely to be self-sustaining...
If urban crow populations are simply self-sustaining, why are so many exploding in size? Immigration is the answer, we suggest...young crows are moving to the cities to exploit their riches.
That is from In the Company of Crows and Ravens, a fascinating book. Most of all this volume stresses how much crows have co-evolved with humankind.
The same day, Michael Vassar wrote me: "One problem I have with
Greg Clark's thesis is that I don't understand how a Malthusian Earth
could have left so much land forested and unproductive. If food was
the limiting factor in population why didn't people clear more land for
farms?" And here's Nick Szabo's challenge to Greg Clark.
Posted by Tyler Cowen on December 4, 2007 at 05:10 PM in Science | Permalink
Comments
It's true that the Malthusian model applies much better to animals than it does to humans. Watching the discovery channel series "planet earth" this became very evident to me. Almost every wild animal must spend all its waking hours trying to stay alive. The only exception I can think of where animals obtain improved living standards happens when people get involved. My golden retriever doesn't have to work all that hard. Could also be true for these crows.
Posted by: Tony Trepanier at Dec 4, 2007 7:32:56 PM
WRT the last point, a lot of prime forest land != prime agricultural land. Just look at the Canadian Shield. It's a very pretty pile of rocks, but...
Posted by: Renee at Dec 4, 2007 8:27:57 PM
How much level land was left forested in England or Japan in 1800? Most tillable land left in England was in royal or aristocratic game preserves with armed guards patrolling it.
Posted by: Steve Sailer at Dec 4, 2007 8:31:06 PM
Lots of animals don't spend every waking hour trying to stay alive -- e.g., dolphins feed themselves in about two hours per day and goof off much of the rest. And many animals spend most of each day sleeping.
Most human hunter-gatherers don't work all that hard, either
Posted by: Steve Sailer at Dec 4, 2007 8:33:54 PM
But isn't it true that for the major part of human history, making land productive required extreme effort, and the productivity of the land wasn't too high? I would imagine that a lot of the "forested and unproductive" land stayed so because, after sinking resources into it, and considering the very high historic discount rates and interest rates (in the range of 30% a year in the Middle Ages), its marginal product was close to zero or negative. This would leave humans crowded on land that was already converted to agriculture, in many cases precisely because it was already the best land that could be farmed using the technology of the day. Of course, every time there was an improvement in agricultural technology (the plow, new varieties of grain, steam thresher, etc.) the marginal productivity of land would increase, leading to eventual expansion of arable areas - but only in the face of continued Malthusian pressure, since technological progress was until very recently not fast enough to keep up with population growth.
Posted by: Rafal Smigrodzki at Dec 4, 2007 8:36:03 PM
Nick Szabo, like a lot of people, lists improvements; but, my impression is that Greg Clark (at least in response to such comments) does not claim a lack of improvements, only no net change. In particular, he seems to claim a trough around 1500, so improvements after that are not direct contradictions to his claim. If that is his claim, I'd like to see an description of this decline. (I haven't read the book, but given the utter failure of commenters to acknowledge this claim, I doubt it is in there.)
Posted by: Douglas Knight at Dec 4, 2007 11:31:49 PM
Maybe a lack of property rights protection prevented people from converting more land to farm land. If the investment in conversion was high then why bother doing it if you couldn't keep what you could produce with the land?
Posted by: Randall Parker at Dec 5, 2007 2:14:53 AM
Vassar's conflation of forested and unproductive doesn't strike me as realistic, unless you're a city boy.
Continuously harvestable forest products include firewood, game, grazing, browse, forage (including acorns), coppice, etc. Other values include shelter, concealment, and famine foods.
As woodland dwindles, value of all these products (and of timber) rises. At some point, the value should be high enough that it would outweigh demands for conversion to farmland in the poorest soils.
Posted by: Mike Huben at Dec 5, 2007 5:47:18 AM
A Radio Japan feature years ago told how crows were mugging people in Tokyo who didn't pony up with a handout.
Sort of a local homeless panhandler problem.
Posted by: Ron Hardin at Dec 5, 2007 5:52:40 AM
It's not clear to me what sort of answer to the question about land use would contradict the thesis that most people, at most points in history, were living in Malthusian societies. For some fallows, the answer will be that the right technology or crop didn't exist yet; for others, that the cost of improving the land (deforestation, animal control, water control) couldn't be recouped from the crops; some lands were protected by elites; and on, and on. But whatever factors limited land use, we can still talk about a society being Malthusian if the population was indirectly limited by the food supply.
Posted by: jt at Dec 5, 2007 6:02:02 AM
Michael Vassar: You can't assume a straight line progression in history. At least in the limited case of the Northeast, land that is forested now was clearcut in the 19th century. Land that in my childhood was dedicated to hay and pasture for dairy cows has grown back to woods as big dairies rely more and more on grain and less on pasture. Forests cut for firewood in the early 19th century regrew as anthracite coal, then petroleum, provided the heat for homes in later years.
Posted by: Bill Harshaw at Dec 5, 2007 8:34:16 AM
Interesting that someone automatically equates forested with non-productive.
To add to the comments above. Farmed land degenerates, particularly using the industrial methods popular today. Once the land is no longer viable for intensive farming, it must be left to grow back into forest to regenerate. We are just lucky that places like Iowa had topsoil that was 5-6 feet deep. Only 2 feet deep now. When that gets to less than a foot, then the farmer will have to look for alternatives.
The Missippi is called the Big Mudy because it is carrying topsoils from thousands and thousands of miles of watershed. That topsoil being carried out to the Gulf will need to be regenerated sometime.
Posted by: techreseller at Dec 5, 2007 12:13:12 PM
It takes thousands of years to generate a good crop 'o topsoil...
Posted by: Renee at Dec 5, 2007 1:24:00 PM
Steve: Yes, but the amount of (uncultivated) land required for hunter-gatherers is huge compared the amount required for agriculture. Global populations pre-agriculture were not more than a million people for a long, long time. Less, probably.
Posted by: Renee at Dec 5, 2007 1:26:13 PM
Maybe those lazy dolphins can be recruited to play football in Miami.
Posted by: Yancey Ward at Dec 5, 2007 5:57:12 PM
Douglas, we have to differentiate two sectors of the economy which follow very different regimes. The first is agricultural, which I agree with Clark up until about 1800 in England was, worldwide over the long term and on average, Malthusian, although I also agree with Randall Park that security of property rights played a large role. Improvements in agricultural technology and institutions (such as better property rights) served to increase population rather than per capita standard of living. The second economic sector is the manufacturing sector, which does not follow the Malthusian law. Improvements in manufacturing technology and institutions increase the per capita standard of living rather than the population. If one just looks at overall statistics, the Malthusian effect dominates where the agricultural sector dominates the economy, and does not where it does not, up to the modern era of effective birth control. A plague (like the Black Death) could temporarily increase the per capita agricultural surplus, and thus standard of living; I suspect this explains a peak in the late 14th century after the Black Death and a trough in 1500 as the population rebounded. Growing literacy and world trade would explain increases after 1500, from both permanent manufacturing improvements and agricultural improvements temporarily racing ahead of population. Note that large "temporary" departures from the Malthusian curve, whether due to plague, mass migration, or improved agricultural technology or institutions, can last more than a century, but probably not much more than two centuries, before the population grows to adjust, during the era before effective birth control.
Clark's data indicate that manufacturing productivity in Europe increased throughout most of the late Middle Ages and at an increasing rate after the rise of literacy in the 17th century. I doubt that this alone caused any long-term departure from the Malthusian curve -- instead feedback into higher agricultural productivity caused us to race temporarily ahead of the Malthusian curve, and other effects (especially effective birth control) have caused a more permanent end to the Malthusian regime in agriculture. Also, worldwide trade made food importing countries (such as England) depart from the Malthusian curve more than the overall global departure, and large emigrations, perhaps including some of those during the colonial era can, like plague, produce temporary increases in per capita standard of living under the Malthusian regime. (Many of these points are just reiterations of Clark's, of course).
Posted by: Nick Szabo at Dec 5, 2007 7:13:12 PM
Doulas Knight: my impression is that Greg Clark (at least in response to such comments) does not claim a lack of improvements, only no net change.
Here is one of several negative comments about the importance of institutions that Clark made during the MR discussion:
"The widespread impression that between 1300 and 1800 England experienced significant institutional improvements is just wrong. There were changes, yes. But not improvements."
This and other statements of his seem to me quite different from my claim: that there were several important institutional improvements during this period, but that their overall effect was mostly higher population rather than higher per capita standard of living, due to the dominance of agriculture in the economy and the resulting Malthusian effect. If we look at just the manufacturing sector we see significant productivity growth all the way back to at least 1500, but for most of the period until 1800 manufacturing was too small a sector of the economy for this to make a large overall difference. But even the overall curve departs significantly from the Malthusian curve after about 1650 in England. The pace of technological and institutional improvements was so fast that they started going into raising the per capita standard of living even as the population still climbed. But the Malthusian effect means that in primarily agricultural economies without modern birth control we can't measure the value of technological or institutional improvements by their effect on the overall long-term standard of living. Instead they will, overall and over the long term, go into increasing the population while the standard of living moves back down towards subsistence.
Posted by: Nick Szabo at Dec 5, 2007 7:31:32 PM
A problem with fitting the late medieval and early modern demographics of western Europe to a Malthusian model is that following the Black Death, there was no rapid population recovery. In most places, the population continued to decline, though not so dramatically, until 1450, and real recovery did not begin until around 1500, a little earlier for northern Italy.
A second episode of widespread population decline lasted through most of the 17th century. The 30 years war is only the most dramatic episode of death and destruction in this time, and in most places, real population recovery did not begin until 1750 or so, with the agricultural and industrial revolutions.
It seems that since at least the early modern period, Europeans have been making household formation decisions based on the ability to give that household a standard of living well above subsistence.
Posted by: Cyrus at Dec 5, 2007 8:26:29 PM
Obviously Michael Vassar has never pulled out a stump.
Posted by: lee at Dec 5, 2007 10:44:54 PM
In most places, the population continued to decline, though not so dramatically, until 1450, and real recovery did not begin until around 1500, a little earlier for northern Italy.
The population declined to 1450 because the plague kept returning. On the MR forum, Clark claims it kept going to 1520, but wikipedia makes it sound more like 1450. Anyhow, the recovery does not sound malthusian to me.
I can't find evidence for my claim that Clark claims an institutional trough, but here's a quote (from MR) that doesn't have him talking stasis:
Comparing 1200 to 1800 we so see a decline in violence. But by 1800 tax rates were much higher, significant inflation had appeared for the first time, there was a huge government debt, and trade was restricted by large scale war with the French, and men in port cities were being kidnapped into the navy. Is that a better setting for economic activity?
One interesting point is that high levels of violence in the 13th century did not prevent large trade and sophisticated finance.
He might have an excessively narrow definition of "institution" as "market option." Perhaps because that lets him measure them.
Posted by: Douglas Knight at Dec 6, 2007 12:58:55 AM
Cyrus,
Might changes in the weather have played a role in preventing population recovery?
Posted by: Randall Parker at Dec 6, 2007 1:12:55 AM
Attribted to Greg Clark:
But [compared to 1200] by 1800 tax rates were much higher, significant inflation had appeared for the first time, there was a huge government debt, and trade was restricted by large scale war with the French, and men in port cities were being kidnapped into the navy. Is that a better setting for economic activity?
These statements are highly misleading. In the late 18th and early 19th centuries royal/parliamentary taxes and debts were surely higher than they were in 13th century, but during those Middle Ages the English economy was dominated by local lords which charged rents what were much higher fractions of tenants' output than the government expenditures of the nineteenth century. These rents were used to supply, among other things, most of England's police, much of its legal system, and most of its military might. By 1800 these feudal systems and their rents had dwindled to insignificance.
Even worse is Clark's convenient focus on the year 1800 itself, a year very uncharacteristic of the general era of the eighteenth and nineteenth centuries. The "significant inflation", "huge government debt", and "restrictions on trade" he cites were all symptoms of the Napoleonic Wars, conditions that did not exist for most of the 18th and 19th centuries surrounding 1800. Besides these temporary burdens the war also temporarily created an exceptional market for many industrial goods, especially iron.
Apart from the temporary departure from the gold standard during the Napoleonic Wars there was (by our modern standards) no significant inflation in 18th and 19th century England. Its currency was far more available and reliable than it was during the Middle Ages. Restrictions on trade, especially in form of guilds and municipal regulations, were severe in many sectors of industry during the Middle Ages. Guilds until the 17th century had the power not only to regulate trades, but to themselves act as governments to prosecutre miscreants -- practices properly criticized by Adam Smith and many others as severe restrictions on free trade. These severe restrictions on trade had been mostly abandoned in the 17th and 18th centuries before Smith wrote, and almost entirely abandoned by 1800 or shortly thereafter. The dawn of the industrial revolution was an era of laissez faire to a degree unimaginable either in the Middle Ages or now.
Posted by: Nick Szabo at Dec 7, 2007 6:00:28 PM
One interesting point is that high levels of violence in the 13th century did not prevent large trade and sophisticated finance.
Good grief. I can't figure out why anybody would repeat claims like these about institutional history as if they were something resembling reality. Thirteenth century England did not have finance anywhere approaching the sophistication of the nineeteenth century. There were no stock or bond markets, no organized commodity futures or commercial paper exchanges, no insurance contracts, no paper currency, no widely published price quotes, no double-entry accounting (indeed, hardly any accounting beyond tally sticks) -- and that's just the tip of the iceberg. There were widespread local price and quality controls from guilds and municipalities that made effective near-monopoligies out of what were in many industries after the 17th century were competitive markets..
Posted by: Nick Szabo at Dec 7, 2007 6:22:22 PM
Crows and humans, as silly as this may sound, do share a lot of the same characteristics. Both of these species enjoy interacting with their fellow comrades and use communication and awareness to promote physical, as well as social, gains. Crows are one of the most obnoxious animals I regularly have to cope with, so the thesis of crows being dependant and prospering off of humans must be the reason I so regulary hear that annnoying screech. I have seen these creatures at work for coulinary compensation, and must admit we don't give them enough credit, their birdbrains are larger than most would expect. And even if their numbers and stats are irregular in comparison to their fellow avian friends, who can blame them for taking the easy way out and leeching onto human kind to better their own existence.
Posted by: chase at Dec 8, 2007 12:02:56 AM
Good grief. I can't figure out why anybody would repeat claims like these about institutional history as if they were something resembling reality.
If you want me to treat Greg Clark as a fraud, why don't you lead by example?
Posted by: Douglas Knight at Dec 9, 2007 8:34:52 PM
