The fertility rate of half the world is now 2.1 or less — “the replacement rate of fertility” (the number that is consistent with a stable population). If current trends continue, sometime between 2020 and 2050 the world’s fertility rate will fall below the global replacement rate.
Mothers in developing countries today can expect to have three children. Their mothers had six.
Richard Tol collected data on climate and conflict in Europe over the past thousand years (”Climate Change and Violent Conflict in Europe over the Last Millennium“).
Until the mid-18th century, the correlation between the number of conflicts and the average temperature is continuously and significantly negative — lower temperatures mean more wars. The line remains close to the 95% confidence level, suggesting there is only one chance in 20 that it is an accidental, random effect. Then, suddenly, the negative correlation vanishes. (The line goes into positive territory, but not enough to be statistically meaningful.)
The researchers suggest that in the more remote past the effects of cold weather on harvests led to supply shortages, and that these increased the likelihood of people fighting over food and the land needed to produce it. They argue that the reason the relationship between warfare and cold vanishes in the mid-18th century is that this is the moment when the industrial revolution began. The food supply increased and improvements in transportationallowed food to be more easily shipped to areas of scarcity.
Farmers could more often produce reasonable yields during colder weather — and long-distance trade provided a buffer against crop failure.
“Cool heads or heated conflicts?,” The Economist
[I]t does not make sense to talk about market efficiency without taking into account that market participants have bounded resources. In other words, instead of saying that a market is “efficient” we should say, borrowing from theoretical computer science, that a market is efficient with respect to resources S, e.g., time, memory, etc., if no strategy using resources S can generate a substantial profit. Similarly, we cannot say that investors act optimally given all the available information, but rather they act optimally within their resources. This allows for markets to be efficient for some investors, but not for others; for example, a computationally powerful hedge fund may extract profits from a market which looks very efficient from the point of view of a day-trader who has less resources at his disposal—arguably the status quo.
“A Computational View of Market Efficiency”
—
“We analyze the intertemporal stability of returns to technical trading rules in the foreign exchange market by conducting true, out-of-sample tests on previously published rules. The excess returns of the 1970s and 1980s were genuine and not just the result of data mining. But these profit opportunities had disappeared by the mid-1990s for filter and moving average (MA) rules. Returns to less-studied rules, such as channel, ARIMA, genetic programming and Markov rules, also have declined, but have probably not completely disappeared. …The most likely time for a structural break in the MA and filter rule returns is the early 1990s. These regularities are consistent with the Adaptive Markets Hypothesis (Lo, 2004), but not with the Efficient Markets Hypothesis.”
“The Adaptive Markets Hypothesis: Evidence from the Foreign Exchange Market”
—
“Have You Reviewed Papers on the Adaptive Market Hypothesis?,” CXO Blog
Research by Paola Sapienza & Luigi Zingales (”Gender differences in financial risk aversion and career choices are affected by testosterone“) suggests that testosterone levels may explain why men dominate risky financial professions.
The researchers measured the amount of testosterone in the saliva of aspiring bankers (MBA students from the University of Chicago). They also estimated the students’ exposure to the hormone before they were born by measuring the ratios of their index fingers to their ring fingers (a long ring finger indicates high testosterone exposure) and by measuring how accurately they could determine human emotions by observing only people’s eyes, which also correlates with prenatal exposure to testosterone.
The students had to decide between a 50:50 chance of getting $200 or a gradually increasing sure payout, which ranged from $50 up to $120. The point at which a participant decided to switch from the gamble to the sure thing was reckoned a reasonable approximation of his appetite for risk.
Women and men with the same levels of testosterone generally switched at the same time, demonstrating similar risk preferences. Women who had more testosterone were more risk-loving than women with less, while the data for men at the lower end of the spectrum displayed a similar relationship. Curiously, the relationship between testosterone and risk taking was not as strong for men with moderate to high levels.
The correlation was strongest when the salivary measure of testosterone was used.
The researchers then followed the subjects’ progress after they graduated, to see what sort of careers they entered. Men were more likely than women to choose a risky job in finance but the difference was accounted for entirely by their levels of salivary testosterone.
Africa is the fastest-growing and fastest-urbanising continent. Its population has grown from 110m in 1850 to 1 billion today. The average African woman born today is expected to have about 5 children, compared with just 1.7 in East Asia. In 1950 there were two Europeans for every African; by 2050, on present trends, there will be two Africans for every European.
The past 15 years have seen Africa’s fastest-ever period of economic growth, & it appears to be following the rest of the world through a demographic transition (falling birth rates as people get richer), which should increase the size (relative, as well as absolute) of their working-age population.
According to a study by the Harvard Initiative for Global Health (”Realizing the Demographic dividend: is Africa any different?” By David E. Bloom), the share of the working-age population will rise in 27 of 32 African countries between 2005 and 2015. On other continents this phenomenon has led to increased productivity.
Africa today produces less food per head than at any time since independence. Only 4% of Africa’s farmland is irrigated.
According to the UN Population Division, Africa’s overall population is 8% lower today than it would have been if its fertility rate had stayed at its 1970s level.
The use of modern contraceptives in sub-Saharan Africa is only 12% (though it has doubled since 1994). The rate in Asia and Latin America is over 40%, so contraceptive use is likely to rise sharply.
J Curve
Unless trends change, by the middle of the century, populations in the most developed countries will have shrunk and the number of retired individuals supported by each person of working age will increase significantly.
A study by Mikko Myrskyla, Hans-Peter Kohler, & Francesco Billari (”Advances in development reverse fertility declines“) suggests that the trend may change: as development continues, the demographic transition goes into reverse.
The researchers looked at two years 1975 and 2005, and analyzed countries using two factors, total fertility rate (the number of children that would be born to a woman in a particular country over the course of her life if she experienced the age-specific fertility rates observed in that country during the calendar year in question) and human development index or “HDI” (a measure used by the UN that includes life expectancy, average income per person, and level of education), which has a maximum possible value of one.
In 1975, of the 107 countries analyzed, the best was Canada, with an HDI of 0.89. By 2005, two dozen countries (of 240 analzyed) had HDIs above nine. In 1975, a graph plotting fertility rate against the HDI fell as the HDI rose. By 2005, though, once the HDI rose above 0.9 or so, it turned up, producing a “J-shaped” curve (the mirror image of a letter J).
In many countries with very high levels of development (around 0.95) fertility rates are now approaching two children per woman.
The nadir of fertility appears to be 1.3 children per woman but this new data suggests the ultimate outcome of development may be zero population growth.
Toxoplasma gondii is a parasite that lives in the guts of cats, where it sheds eggs in cat feces that are often eaten by rats. The parasites increase their odds of getting back to cats by changing the infected rats’ brains, making them less scared of cats (and so more likely to be eaten).
A new study by Jaroslav Flegr, Jan Havlíček, et. al, (”Increased incidence of traffic accidents in Toxoplasma-infected military drivers and protective effect RhD molecule revealed by a large-scale prospective cohort study“) found that subjects with high titers of anti-Toxoplasma antibodies had a probability of a traffic accident (17%) more than 6 times higher than Toxoplasma-free subjects.
Angus Maddison has estimated that life expectancy during the first millennium AD averaged about 25 years (lots of children died very young and many of the rest survived to middle age). Many more children survived into adulthood after the Industrial Revolution and by the beginning of the 20th century average life expectancy in America and the better-off parts of Europe was close to 50. By mid-century the gains from lower child mortality had mainly run their course & the extra years were coming from higher survival rates among older people. The UN thinks that life expectancy at birth worldwide will go up from 68 years at present to 76 by 2050 and in rich countries from 77 to 83 (women generally live 5-6 years longer than men).
Jim Oeppen and James Vaupel have charted life expectancy since 1840 (”Enhanced: Broken Limits to Life Expectancy“), joining up the figures for whatever country was holding the longevity record at the time, and found that the resulting trend line has been moving upward by about 3 months a year.
In the US, centenarians are the fastest-growing section of the population, with an increase from 3,700 in 1940 to over 100,000 now.
According to Robert Fogel, Western people’s average body size has increased by 50% over the past 250 years. And larger body size is correlated with better health and longer life.
According to the UN’s latest biennial population forecast, the median age for all countries is due to rise from 29 now to 38 by 2050. At present just under 11% of the world’s 6.9 billion people are over 60. By 2050 that share will have risen to 22% (of a population of over 9 billion), and in the developed countries to 33%.
In 1900 average life expectancy at birth for the world as a whole was only around 30 years, and in rich countries under 50. The figures now are 67 and 78 respectively.
In the early 1970s women across the world were, on average, having 4.3 children each. The current global average is 2.6, and in rich countries only 1.6. By 2050 the global figure will have dropped to just two, and the world’s population will begin to level out.
“A slow-burning fuse,” by Barbara Beck
Non-kin altruism among non-human animals is rare, & altruism fares poorly in computer simulations — when altruistic individuals emerge in a community characterized by self-interested behavior, selfishness triumphs.
Group selection could explain the prevalence of human altruism but probably only if the ancestral environment included high levels of violence and inbreeding.
Sam Bowles showed in 2006 that genetic analyses of tribes still living a Stone Age life suggests there was enough inbreeding to make group competition a driver of genetic change.
In ancient graves excavated previously, Bowles found that up to 46% of the skeletons from 15 different locations around the world showed signs of a violent death. More recently, war inflicted 30% of deaths among the Ache, 17% among the Hiwi, & just 4% among the Anbara. Combat between groups accounted for about 14% of all deaths in these hunter-gatherer societies.
After estimating the rate that altruism would reduce an individual’s chances of reproducing, Bowles plugged the numbers into a model of intergroup competition where an individual’s altruism would also improve a group’s chances of combat triumph. In the absence of war, a gene imposing a self-sacrificial cost of as little as 3% in forgone reproduction would drop from 90% to 10% of the population in 150 generations. Bowles predicts that much higher levels of self-sacrifice — up to 13% in one case — could be sustained if warfare were brought into the equation.
“Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?” By Samuel Bowles
“Altruism’s Bloody Roots,” by Brandon Keim
“Ancient warfare: Fighting for the greater good,” by Ewen Callaway
“Blood and treasure,” The Economist