Development and Growth Lec 12. Population (2) Bonn University Lingwei Wu

Transcription

1 Development and Growth Lec 12. Population (2) Bonn University Lingwei Wu

2 Today Determinants of population growth Crop and population Potato Maize Sweet potato Nathan Nunn and Nancy Qian The Potato s Contribution to Population and Urbanization: Evidence From A Historical Experiment

3 Introduction Between 1000 and 1900, world population grew from under 300 million to 1.6 billion The determinants of these phenomena have been of much interest to economists, demographers, and historians alike population increase and factors such as per capita incomes, see Galor and Weil (2000), Jones (2003), and Voigtlander and Voth (2006). the determinants of increased life expectancy, see the literature review provided by Cutler, Deaton, and Lleras- Muney (2006)

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5 Background: virtues of the potato Potatoes provide more calories, vitamins, and nutrients per area of land sown than other preexisting Old World staple crops William Langer (1963, p. 14) argues that within Europe the spread of the potato culture everywhere corresponded with the rapid increase of population.

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7 The Merits of Potatoes 1. From a nutritional standpoint, potatoes were superior to preexisting staple crops because they provided more vitamins and nutrients and they provided a greater supply of calories. 2. They require less land to produce the same amount of calories 3. Their cultivation did not require a complete switch away from the cultivation of Old World staples; it was possible to plant potatoes between the growing seasons of other crops 4. Potatoes also provided indirect benefits. Being relatively easy to store, potatoes provided excellent fodder for livestock (primarily pigs and cattle), especially through the winter.

8 The Potato s Diffusion from the New World to the Old World

9 The Diffusion Pre-Columbian cultivation occurred within modern-day Colombia, Ecuador, Peru, Bolivia, Chile, and Northern Argentina For the Old World, the potato was discovered along with the discovery of the Americas. The first evidence of potatoes being consumed in Europeans from Seville, Spain After Spain, the potato next appeared in Italy in 1586, then England in 1596 and Germany in 1601

10 The Potato Eaters (Dutch: De Aardappeleters), oil painting by Vincent van Gogh painted in April 1885 in Nuenen, Netherlands

11 Other New World Staple Crops Is there a bundle of new world crops transfer? maize, cassava, tomatoes, chili and bell peppers, cacao, sunflowers, and the sweet potato Maize unable to rival potatoes in terms of nutrients or calories. It produces significantly fewer calories per acre of land. Sweet potatoes are also nutritious and produce similar amounts of calories per acre of land as potatoes but sweet potatoes, transported by Polynesians, reached the Old World long before the European discovery of the New World. For many countries in our sample, their impact would have been felt as early as 1000 a close substitute to the sweet potato, the yam, already existed in the Old World

12 Data Crop Suitability the Food and Agriculture Organization (FAO) s Global Agro Ecological Zones (GAEZ) 2002 database. These data measure the suitability for cultivating individual crops at a very disaggregated geographic level. Sample Observations are at the country-year level. All regressions use a baseline sample of 130 Old World countries. Countries in North and South America are excluded. The periods are 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1750, 1800, 1850, and1900

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15 V. EMPIRICAL STRATEGY AND MAIN Challenge RESULTS there is an issue of reverse causality. The adoption of potatoes might have caused population growth, but alternatively, latent population pressure and the associated demand for food might have caused the adoption of potatoes. Diff-in-Diffs

16 Diff-in-Diffs i: countries t: time periods, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1750, 1800, 1850, and 1900 ln PotatoArea is the natural log of the total amount of land that is suitable for potatoes I t Post is an indicator variable that equals one for the periods after 1700 (i.e., 1750, 1800, 1850, and 1900)

17 A standard DD strategy Merits: it allows us to control for both country and timeperiod fixed effects all time-invariant differences across countries such as geography, food preferences, or institutions (to the extent that they change slowly over time) are controlled for all secular changes over time such as global improvements in health, sanitation, and technological advancements are controlled for Assumption: The strategy relies on there being no other shocks occurring around the same time that potatoes were adopted that are correlated with countries suitability for potato cultivation.

18 The DID Results

19 When we have multiple periods We can do flexible estimates, and test the pre-trend Similar practice to Duflo (2004) Flexible estimates Use interaction terms between Potato Area and each year dummy

20 Population

21 Base year=1000

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23 Population

24 Urbanization

25 Placebo tests: rolling estimate A check for our chosen cutoff date is similar in spirit to tests for structural breaks. Use hypothetical cut-offs of Post.

26 Population

27 Placebo tests: rolling estimate A check for our chosen cutoff date is similar in spirit to tests for structural breaks. Use hypothetical cut-offs of Post.

28 Population

29 Placebo tests: rolling estimate A check for our chosen cutoff date is similar in spirit to tests for structural breaks. Use hypothetical cut-offs of Post.

30 Population

31 Placebo tests: rolling estimate A check for our chosen cutoff date is similar in spirit to tests for structural breaks. Use hypothetical cut-offs of Post.

32 Population

33 Placebo tests: rolling estimate A check for our chosen cutoff date is similar in spirit to tests for structural breaks. Use hypothetical cut-offs of Post.

34 Population

35 Robustness 1: alternative definition of potato suitability

36 Robustness 2: Additional time- and country- varying factors

37 Robustness 3: Examining within Continent Variation

38 Robustness 4: Adult Soldier Heights within France

39 Summary of results 1. They exploit regional variation in suitability for cultivating potatoes together with time variation arising from their introduction to the Old World from the Americas to estimate the impact of potatoes on Old World population and urbanization 2. The results show that the introduction of the potato was responsible for a significant portion of the increase in population and urbanization observed during the eighteenth and nineteenth centuries

40 Discussion & Thoughts The results are largely driven by Europe Why: Better suitability High population growth after the Industrial Revolution (after the cutoff year) The adoption at India, Indonesia, and Japan was later (preliminary at 1700) What else: Can make use of the information of timing The potential substitutes of New World Crops

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42 Population

43 The different timing

44 Next: Maize Chen and Kung (2016) Of maize and men: the effect of a New World crop on population and economic growth in China The new crop on population: maize accounted for a nearly 19% increase in the Chinese population during

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46 Three routes

47 When the New World crops came to China Which will obtain popularity? A matter of taste? Suitability matters: 10% for potato, and 55% for maize

48 The Diffusion of Maize in China:

49 Data Within country investigation At prefecture level A panel of maize adoption: Gazetteers Both population and urbanization A panel:

50 Identification strategy Specification where i indexes a prefecture (fu), t indexes a time interval, and popden (in natural log) stands for the population density of prefecture i in 1600, 1776, 1820, 1851, 1880 and The key explanatory variable of interest is M it, a dummy variable that equals to 1 if maize was adopted, and 0 otherwise, in prefecture i.

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52 Test the pre-trend

53 Control for Positive Checks By Malthus, factors such as war and epidemics, which affect population outcomes by increasing mortality, have a significant and negative effect on population density

54 Did maize induce Positive Checks?

55 Did maize induce more urbanization?

56 Did maize induce a higher level of income?

57 Discussion: Population growth with/without economics development New crops A type of agricultural technology improvement The potatoes The maize Both have significant contribution in population growth: clear channel (an increase in food productivity better living standards, and fertility and life expectancy to increase) But only potatoes had resulted in better economic development in the long run The Malthusian and Post-Malthusian regime: technology advancement th century in Europe, but not in China

58 Further Discussion & Thoughts By the analysis of potatoes The new crop higher rate of urbanization In the specific context of China New crops had no effects on urbanization and wages Are the urbanization results driven by Europe as well?

59 Extensions: crops and development 1. The Irish Famine & Potatoes 2. The role of sweet potatoes in mitigating conflict

60 The Irish Famine & Potatoes The Irish Famine took place in Ireland from 1845 to A fungus spread infected potato harvests and caused the disease called Blight Potato. At this point the Irish diet depended on a small range of varieties of potatoes that did not resist the disease. Indigenous people in the Americas varies types of potatoes A single type of potato in Ireland This situation was one of the most devastating ecological disasters of the sixteenth century in Europe (Connell 1962; Mokyr 1981; Mokyr and Ó Gráda 1984)

61 Ireland's population from 1800 to 1920

62 Reported deaths in Ireland from 1843 to 1852

63 migrant population from Ireland to the United States from 1842 to 1855

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66 The sweet potatoes and conflicts Jia (2013) Weather Shocks, Sweet Potatoes And Peasant Revolts In Historical China To what extent did weather shocks cause civil conflict? And to what extent did the historical introduction of (drought resistant) sweet potatoes mitigate these effects? Findings Before the introduction of sweet potatoes, exceptional droughts increased the probability of peasant revolts by around 0.7 percentage points After the introduction of sweet potatoes, exceptional droughts only increased the probability of peasant revolts by around 0.2 percentage points.

67 The diffusion of sweet potato

68 Weather shocks and grain price

69 Weather shocks and revolts

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71 The mitigating effect of sweet potatoes

72 Appendix: How GAEZ calculated the suitability indexes (1) The FAO first collected information on the characteristics of 154 different crops. These data were used to determine what environmental conditions are required for the cultivation of each crop. The FAO then compiled data on the environment for grid cells, spanning the entire globe. Each cell is 0.5 degrees by 0.5 degrees. precipitation, frequency of wet days, mean temperature, diurnal (i.e., daily) temperature range, vapor pressure, cloud cover, sunshine, ground-frost frequency, and wind speed. The second set of characteristics are land characteristics and are taken from the FAO s Digital Soil Map of the World. The final characteristics the slope of soils, which is from the GTOPO30 Database, developed at the U.S. Geological Survey (USGS) EROS Data Center. then calculated an estimate of the potential yield of each crop in each grid cell, given an assumed level of crop management and input use.

73 Appendix: How GAEZ calculated the suitability indexes (2) how many days for cultivation: the FAO determined the starting and ending dates of the length of growing period(lgp) for each crop and grid cell. calculate the potential yields are determined For each crop, constraint-free crop yields were determined, and the yield in each grid-cell was measured as a percentage of this benchmark. A weighted average of the suitability is calculated from grid cells to country level In this paper The authors define land to be suitable for cultivation if it is classified in the database as being either very suitable( percent), suitable(60 80 percent), or moderately suitable. (40 60 percent)