I don’t know if I’m cherry picking information, but it does seem that getting to/being at $5000 or so per capita income results in major changes to a society.
- The total fertility rate (the number of children born per woman) starts at roughly 6-7 in the lowest income countries. However by the time per capita income increases to $5000 per capita the rate has dropped to about 2.6. It goes slightly lower than that as per capita income goes up, but not by much (it usually stabilizes at 1-2). The biggest drop in TFR occurs from per capita income increases up to about $5000
- Democracy takes hold better in nations with per capita incomes close to $5000. While studying the transition from authoritarian to democracy Adam Przeworski found that nations with per capita incomes below $3000 almost always failed in the transition, but nations with per capita incomes of $6000 or higher almost always succeeded.
More recently Adam Przeworski of New York University confirmed this truism by studying every attempted transition to democracy around the globe. He and his colleagues found that once a country passes $6,000 in per capita income it is virtually guaranteed to succeed in its transition to democracy. States between $3,000 and $6,000 have less than a 50-50 chance of staying democracies. And countries below $3,000 are almost bound to fail.
- Happiness (subjective well being, the ability to enjoy life) grows as income grows. But then it plateaus around $5000 per capita national income. A nation with a per capita income of $5000 is happier than one with a $1000 income, but not much less happy than a nation with a $40000 per capita income.
- The Kuznet curve varies with type of pollution, but it shows that pollution increases as per capita income increases, then starts to decrease with further increases in per capita income. Generally the transition occurs in the $3000-$10000 per capita income range.
- Life expectancy grows dramatically, then levels off around $5000 per capita income.
So is it that as a nation reaches $5000 in wealth they can obtain enough medicine, agriculture and shelter that they can focus on quality of life instead? Is it Maslow’s hierarchy of needs on a societal level? Life expectancy, fertility rate and subjective well being all tend to plateau at around $5000 while advances start to be made on pollution and democratic reform.
Many of the biggest problems facing humanity (pollution, overpopulation, authoritarian governments) seem to undergo major changes at roughly $5000 per capita income. Should this be a goal of developing countries, to reach about $14/day in income? There are attempts to rise above $1/day and $2/day levels of income, but reaching middle income status ($3000-10,000 per person) seems to be where the biggest changes occur.