The Industrial Revolution kicked off the fertility transition

Wednesday, September 21st, 2022

It is ironic that our species, which is defined by our big brains, is evolving to become stupid, George Francis says:

Countless articles of scientific research have found the less intelligent to be having more surviving offspring and breeding faster than the intelligent. The problem was noticed by Darwin and his contemporaries, yet it has mostly been ignored throughout the 20th century. Recently it has had a small yet significant revival with the cult classic book At our Wits’ End, and large genetic databases showing intelligence decline. It has even been featured in the Telegraph.


The famous studies of dysgenics in the UK biobank show there is selection against intelligence but don’t attempt to quantify its size. The famous Icelandic study shows dysgenics but only attempts to measure its effect on years in education, not intelligence itself.


The Industrial Revolution kicked off the fertility transition. Countries that became rich were able to prevent starvation and improve health so the number of surviving children skyrocketed. Then with the advent of contraception, abortion and enjoyable alternatives to raising children, fertility plummeted. Many of the poorer, less intelligent countries started this process later meaning that as the natives of smart countries shrink in their population, the low IQ countries are still rapidly expanding.


My favourite estimate of the rate of dysgenics comes from Woodley’s calculation in At Our Wits’ End. He takes the Icelandic estimate for the rate of dysgenics on the educational attainment (years in education) polygenic score, adjusts it for the higher heritability of intelligence (about 80% heritable) and estimates a 0.8 IQ point decline per decade. That’s a lot. My guess is that this is an overestimate. Education attainment correlates negatively with fertility because it captures both the effect of intelligence and the effect of education, creating an overestimate. On the other hand, years in education is less heritable than IQ, causing the unaltered Icelandic estimate of about 0.3 IQ points to be an underestimate.

This is tricky, so let’s be cautious, split the difference and round up. IQ is falling by 0.6 points a decade.

In 1950 the average genotypic IQ was around 93.6. If you are not a high school graduate you need an IQ of 93 to join the US military. In 1950 something like half of the world’s population was too dumb to be in a professional army. Currently, the global average IQ is around 85 and by the end of the century, it will be 74. Then only an elite fraction would be capable of even being part of a professional army.

Average global IQ of 74 — dysgenics is a big problem! Let’s try and narrow it down a bit more. In Francis and Kirkegaard (forthcoming) we estimate that each national IQ point is associated with a 7.8% increase in GDP per capita. We also estimate the economic effects of dysgenics in that paper slightly differently, but with similar results. Let’s imagine the world is one country with an average IQ of 74 in 2100 and an average IQ of 85 as of 2020. The maths works out as a difference of logs at [exp((74–85)*7.8%) –1] = –58%. The effect of this dysgenic decline will be to cut GDP in half! And of course, that doesn’t even begin to consider the intangible factors GDP doesn’t necessarily include: low crime, social trust, science, culture and the arts.

Climate change is currently predicted to cost us a whopping 4% of world GDP by 2050. My numbers imply dysgenics will cost us 30% of GDP by 2050.

(Hat tip to Arnold Kling, who says, “Have a nice day.”)


  1. Jim says:

    “Why wouldn’t you let me solve this for you, anon? We could have conquered the stars themselves!”

  2. Shadeburst says:

    The secular effect aka the Flynn effect is the effect of better nutrition on IQ, during pregnancy as well as on the growing child. In developed societies, the lower IQs are outbreeding the smarties. Globally the secular effect has raised IQ.

    The outcome of the IQ drop in developed nations is that increasing numbers of jobs become beyond the capability of lower IQs. Regrettably among certain political groupings there is no such thing as low IQ. All those people are being left to wither on the vine. Welfare recipient is their only career option.

  3. TRX says:

    Didn’t someone make a movie about that? Why, yes, they did: “Idiocracy.”

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