Have crows avoided a Malthusian equilibrium?

by on December 4, 2007 at 5:10 pm in Science | Permalink

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.

1 Tony Trepanier December 4, 2007 at 7:32 pm

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.

2 Steve Sailer December 4, 2007 at 8:31 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.

3 Rafal Smigrodzki December 4, 2007 at 8:36 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.

4 Randall Parker December 5, 2007 at 2:14 am

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?

5 Ron Hardin December 5, 2007 at 5:52 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.

6 Bill Harshaw December 5, 2007 at 8:34 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.

7 Renee December 5, 2007 at 1:24 pm

It takes thousands of years to generate a good crop ‘o topsoil…

8 Yancey Ward December 5, 2007 at 5:57 pm

Maybe those lazy dolphins can be recruited to play football in Miami.

9 Nick Szabo December 5, 2007 at 7:31 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.

10 lee December 5, 2007 at 10:44 pm

Obviously Michael Vassar has never pulled out a stump.

11 Randall Parker December 6, 2007 at 1:12 am


Might changes in the weather have played a role in preventing population recovery?

12 Nick Szabo December 7, 2007 at 6:22 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..

13 Douglas Knight December 9, 2007 at 8:34 pm

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?

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