Saturday, March 25, 2006

Mercedes Pascual

by Edward Hugh


One of my greatest personal weaknesses - and I would be the first to recognise this - is that I hardly finish thinking about one problem before I start to get interested in another. The issue of global demography and macro economic theory is, unfortunately, no exception here. I am now in a position where I think I see some interim 'closure' (basic hypotheses, simple back-of -the-envelope models) in sight (or at least attainable in a limited time horizon), but I can also now see only too clearly that this problem forms just one part of a much bigger picture of interconnections and feedback processes. In particular these processes seem to be:

1/ Global demographic changes and their economic impact
2/ Global resource depletion
3/ Global climatic changes

This weblog is an ongoing process of exploration, but the main interface is, and will continue to be a demographic one. However it is going to be impossible to maintain a hard-and-fast frontier for something which is, by its very nature fluid.

A good example of this fluidity is to be found today in a paper which is published online this week in the Proceedings of the National Academy of Sciences. The issue is malaria, and just how the process of global climatic change interacts with the mosquito population which inhabits the highlands of East Africa, and how changes in the mosquito population interact with the human population which shares the same habitat.

Which brings us to the work of Mercedes Pascual. As Scientific American informs us:

Since the 1970s, the highlands of East Africa have witnessed a surge in malaria outbreaks. Because the mosquitoes that carry the disease do not thrive in cooler climes some researchers have suggested a link between this rise and climate change. A 2002 study found no such connection, but a new analysis of the data--including five more years of records--seems to show that a modest increase in temperature could lead to a population boom in mosquitoes and, therefore, malaria....

Pascual and her co-workers found that "even a small increase in temperature in these locales can quickly tip the balance in the insects' favor, leading to more mosquitoes and, hence, more vectors for the malaria parasite." However caution is advisable since "this study does not prove that climate change is responsible for the increase in the malaria plaguing African highlands", it should however "be taken into account along with other factors such as treatment resistance and land-use changes".

Of course it should not escape our notice that the other two potential influences mentioned also form part of similar interconnected processes. Essentially I will be following more attentively the climatic and resource issues on my own blog Bonobo Land (and here, and here, and here), but no doubt they will inevitably from time to time 'erupt' here on Demography Matters.

Here is the research interest profile which Mercedes Pascual herself offers on her webpage:

I am a theoretical ecologist interested in population and community dynamics. My research areas encompass: (1) The spatio-temporal dynamics of nonlinear ecological systems for antagonistic interactions (predator-prey, host-parasite, and disturbance-recovery), particularly approaches to scale-up systems from small, individual, levels to more aggregated, population, levels, and approaches to incorporate implicitly in simple (highly aggregated) temporal models the effect of smaller scales. Similar questions are being addressed on the dynamics of infectious diseases in networks. (2) The response of nonlinear ecological systems to environmental variability and the application of nonlinear time series analysis to identify key environmental drivers and to predict responses. In particular, the nonlinear dynamics of infectious diseases in response to climate variability and climate change, including aspects of evolutionary change in pathogens. The main disease under study is cholera, but work is also underway on malaria and influenza. (3) The relationship between structure and dynamics in large networks of ecological interactions (consumer-resource and parasitic links).

In conclusion I would just like to cite one of the central points so often made by the anthropologist Hillard Kaplan: "life is an energy harvesting process". I think it is as simple and as complex as that.

You can find more background links to the latest paper by Mercedes Pacual and her co-workers here and here.

Information on the working group on Global Change and Infectious Disease at the National Center for Ecological Analysis and Synthesis can be found here, and one of their publications can be found here.

The US National Center for Ecological Analysis and Synthesis can be found here. Also the webpage of the "Seasonality and the population dynamics of infectious diseases" project which is lead by Mercedes Pascual and Andrew Dobson can be found here.

This paper (from 1992) by Jonathan Patz - A human disease indicator for the effects of recent global climate change - is also fairly relevant.

Finally, what is the relevance of all this for economic analysis? Well this obviously can't be answered in any satisfactory way here, but just as a clue, let's think about the UN sponsored Global Millenium Project lead by Jeffrey Sachs. I have a problem with the whole line of approach that Sachs is pushing at the moment, since I think it is hopelessly simplistic (which is a pity, since at the end of the 90s he was doing some pretty interesting work with Jeffrey Williamson on demography and development, and here). Now Sachs is pushing the health issue, and this is obviously important, but unless we get to grips with the whole damn complex situation, I fear his initiative will only lead to disappointment and yet more frustration. More posts on this to come, as and when.....

11 comments:

S.M. Stirling said...

Note that northern and western Europeans and their overseas descendants have historically always had a rather distinctive demographic regime.

Prior to the mid-18th century, this was characterized by relatively late age at marriage (usually mid-20's for women, a little later for men), and a high percentage of never-married individuals, sometimes as high as 25%.

This is a stark contrast to most parts of the world, where historically generally occurred soon after puberty (particularly for women) and was nearly universal.

Among northern and western Europeans (north and west of a line roughly between St. Petersburg and Trieste) age at marriage was closely sensitive to economic conditions.

There was what amounted to a strong cultural taboo on having two married couples under the same roof. Couples had to amass sufficient resources to establish their own 'hearth' before marrying; and reproduction outside marriage was quite rare.

Hence birth-rates were, by world standards, always low, and they were inversely proportional to income -- the wealthier the family, the earlier children (particularly women) married and the more children they had. The very poor generally didn't marry at all.

Edward Hugh said...

Hi, thanks for all your interest and comments, some of which I agree with, and about some of which I'm not so sure.

"This is a stark contrast to most parts of the world, where historically generally occurred soon after puberty (particularly for women) and was nearly universal."

This picture really isn't as simple as this, although it is a story many economists like to tell one another.

The Reverend Richard Jones - writing in the mid nineteenth century - was already aware that in agricultural societies delayed marriage was widespread.

He in fact said “this self-restraint is so far exercised that there is no record of the customary age of marriage having at any time, in any country, coincided with the age of puberty.”

He could find no record of this puberty driven fertility, even then. Modern anthropological research has only tended to confirm this, as has much historical research.

In fact strict 'biologically driven' reproductions is extremely rare in human populations, the hutterites maybe?

As you are indicating when people break out of the norm - as in the case of the hutterites, there may well be strong religious or other cultural explanations.

So.

"Hence birth-rates were, by world standards, always low,"

I doubt this. They were never as high as people generally are want to imagine they were. What is happening now in places like Mali, Niger etc is a distinctly modern phenomenon.

"and they were inversely proportional to income -- the wealthier the family, the earlier children"

Yes, this certainly seems to have been true. Yet in the modern era the situation has inversed, with the population groups with more 'nett worth' having progresively less children and having them later. ie the income effect seems to have inverted. This is a major behavioural shift, and the interesting (I would say billion dollar) question is just what produces this shift?

Incidentally you note in another comment that non-hispanic white republican and democrat voters have different fertility levels in the US, you wouldn't happen to have any data on the relevant female educational and occupational levels to go with this would you?

S.M. Stirling said...

"The Reverend Richard Jones - writing in the mid nineteenth century - was already aware that in agricultural societies delayed marriage was widespread."

-- yeah, but he was working mostly from data about societies in the area I was describing.

The distinction is between cultures where multigenerational households were common, and those in which they weren't.

Eg., average age at marriage for Russian or Serbian female peasants in the 19th century was something like 8-10 years lower than for their French or English counterparts, and marriage rates much higher.

They married in their teens; the westerners, in their mid twenties.

(Keep in mind that puberty typically occurred at 15-17 back then.)

Likewise, note that in China the marriage rate historically approached 100% (and still does), whereas in Europe it was often as low as 75% and rarely above 90%.

Only in the last 50 years or so have higher rates of never-married individuals and of later marriage begun to spread outside their original source areas among NW Europeans and their overseas descendants.

>I doubt this. They were never as high as people generally are want to imagine they were.

-- Crude birth rates in England were usually below 35/1000 and often as low as 25/1000, which for preindustrial populations are _extremely_ low. Typical rates in most of Africa, the Middle East and South and East Asia were in the high 30's or the 40's per 1000, corresponding with a TFR of around 7 or higher and a very low percentage of never-married women.

European birthrates were often too low to keep the population from shrinking; hence the prolonged periods of declining population you find in, eg., British demography. The 18th and 19th centuries stand out as an unusual "blip".

S.M. Stirling said...

>Yet in the modern era the situation has inversed, with the population groups with more 'nett worth' having progresively less children and having them later.

-- temporarily. What seems to have happened is a shift that started in the upper income groups and has been, in a multigenerational process, spreading to the lower ones.

>Incidentally you note in another comment that non-hispanic white republican and democrat voters have different fertility levels in the US, you wouldn't happen to have any data on the relevant female educational and occupational levels to go with this would you?

"But at higher incomes, Republicans have significantly more children. For example, white "Strong Republicans" with incomes of $50k or more average 2.16 children versus 1.62 children for white Democrats of either "Strong" or "Not Strong" fervency of the same income range.

At $90k and above, "Strong Republicans" average 2.47 children versus 2.04 kids for "Not Strong Republicans," and 1.56 for Democrats as a whole. The sample sizes are little small for slicing and dicing too narrowly, but the pattern seems apparent."

http://72.14.203.104/search?q=cache:Or5yy-6w2-oJ:www.isteve.com/babygap.htm+Republican+Democrat+TFR+fertility&hl=en&gl=us&ct=clnk&cd=1&ie=UTF-8

Edward said...

"temporarily"

I'm not sure why you imagine this is only going to be temporary. I would say that is was long term, and sustainable, and that fertility globally will trend downwards with increasing life expectancy and the steady movement forwards of the technology frontier which will mean age on partnership formation and first childbirth will continue to trend upwards with the increasing number of years of preparation required.

fertility globally will trend downwards ..... with the notable exception of strong republicans in the US, evidently. Thanks for this.

Edward said...

"Note that northern and western Europeans and their overseas descendants have historically always had a rather distinctive demographic regime."

Yes, I think historically these things are important. What I was getting at was fertility ex-Europe. Outside China, where as you note there was early and extensive marriage (but not menarche), and where there seems to have been an early version of stopping behaviour. we don't have much hard data to go on for agricultural societies, but since there was property involved, and extensive use of 'dowry related' cultures it seems unreasonable to imagine that they were marrying especially young. What evidence we have from foragers and hunter gatherers again points to the broad phenomenon of 'natural fertility' with reproductive activity way below 'biological reproduction' and little evidence of menarche driven reproduction. "They produce like mice" seems to be the sort of thing only economists believe, especially since we are much more like other higher primates then ever we are like mice.

Edward said...

"but not menarche"

Sorry, what I meant was not at menarche age.

Hoosier said...

"Prior to the mid-18th century, this was characterized by relatively late age at marriage (usually mid-20's for women, a little later for men), and a high percentage of never-married individuals, sometimes as high as 25%.

This is a stark contrast to most parts of the world, where historically generally occurred soon after puberty (particularly for women) and was nearly universal."

could you give me the source for this? I am no expert but given average life expectancy of 40-45 years in those times I tended to assume that age at marriage was late teens to early twenties for women and 3-4 up to 10 years for men.

I also find hard to believe there were significant demographic differences between traditional Western and Eastern European populations. The Western countries enjoyed more rapid population growth after 16-17th century, coinciding with expansion of trade and with it the budding of capitalism ( production for trade instead of for local consumption in the local agrarian community) as well as with the Reform.

The last time the economy in Western Europe was similar with that in Eastern Europe is in mid 17th century when after the 30 Years War - France, German states and Poland were so broke and weakened that the Ottomans could advance to Vienna and the Russians pushed the Poles west of Nieman and out of Ukraine. I'm not sure where you would include Poland as the line from St. Petersburg to Trieste puts it mostly in the Eastern part, even though culturally and socially they were closer to the other central Europeans. But as they decline I assume they go on the losers side.

Early 17th century is an age of flourishing for both Russia and the european teritories of the Ottomans. After 1650 the English get ahead the Dutch and then the French. The Prussians and the Austrians grow in mid Europe. The Swedes rule unchallenged the Baltic area. Peter the Great tries to push Russia on the same path in early 18th century but largely fails. The Ottomans state begins to decompose slowly and will take 200 years before anything resembling capitalism happens in the Balkans. But by then the British Empire rules the world, America becomes one of the top 3 world economies and France and German states follow them close. of note that also after 1650 Spain and Portugal decline despite being the most succesful early European colonial powers.

my whole point is that the demographics and reproduction behaviors likely become different with the transition from traditional/ agrarian/feudal societies to the modern/capitalist societies. "dowry and hearth" is a big part of behavior towards family and reproduction in eastern societies including the Muslim ones.

In the agrarian society the rule was also different - the more affluent who had land tended to have fewer MASCULINE children ( the girls did not count as much) as the father did not wish to split his land in too many lots. as the childhood mortality was high even for the mid and upper classes families were numerous. however once the boys reached teenage years some were pushed either towards arms or to become priests or monks. These young men did not get to reproduce, or if they did their offspring would be illegitim and remain in the lower/servant classes. Reform erased the last option for North Europeans but this has coincided with the raise and expansion of capitalism so it is hard to discerne their effects separately.

If we think only of America one can easy observe that this was the foremost capitalist state. The only exception to the rule was the slavery that was rather an exception than the rule. America had too few ( and already self selected mid class when they came here) white people. Europe had plenty of white indentured people to need any black slaves. So I tend to belive the rule of birthrates that were proportional with the wealth of a family applied to Americans but very likely not to Europeans ( including British or Germans the main ethnic stock of the white Americans).

and I reckon the interplay between demographics and economic growth goes both ways.

Edward Hugh said...

Hi Hoosier,

Just to let you know I have seen your various comments, and since they ask extensive questions I will try to find the time to answer them wit the seriousness they deserve over the weekend.

Edward Hugh said...

Hi

"could you give me the source for this? I am no expert but given average life expectancy of 40-45 years in those times I tended to assume that age at marriage was late teens to early twenties for women and 3-4 up to 10 years for men."

Sorry for the delay, but better late than never I hope. Basically the issues here are really very extensive, and I'm afraid time is pressing, but a good source on all of this is the US Economic Historian Gregory Clark. He has written extensively on the european family, fertility, the Malthusian regime and things like that. You can find a good selection of material on his web page here.

Basically I learnt a lot from reading Clark, and the references you can find in his papers, at one point. At some stage I would really like to go back to all of this, but I doubt that stage is going to be any time soon, undortunately.

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