Infertility rates are rising and nobody seems to quite know why. Below is what feels like a possible (trivial) explanation that I haven’t seen mentioned anywhere.
a family is either fertile or infertile, and fertility is hereditary
the modal fertile family can have up to 10 kids, the modal infertile family can only have 2 kids
in the olden days families aimed to have as many kids as they could
now families aim to have 2 kids each
Under this model, in the olden days we would find a high proportion of fertile people in the gene pool, but in the modern world we wouldn’t. Put differently, the old convention lead to a strong positive correlation between fertility and participation in the gene pool, and the new convention leads to 0 correlation. This removes the selective pressure on fertility, hence we should expect fertility to drop / infertility to rise.
Empirical evidence for this would be something like an analysis of the time series of family size variance and infertility—is lower variance followed by increased infertility?
Regarding female fertility, this report from Norway outlines the trend that I vaguely thought was representative of most of the developed world over the last 100 years.
Female fertility is trickier to measure, since female fertility and age are strongly correlated, and women have been having kids later, so it’s important (and likely tricky) to disentangle this confounder from the data.
Infertility rates are rising and nobody seems to quite know why. Below is what feels like a possible (trivial) explanation that I haven’t seen mentioned anywhere.
I’m not in this field personally so it’s possible this theory is out there, but asking GPT about it doesn’t yield the proposed explanation: https://chat.openai.com/share/ab4138f6-978c-445a-9228-674ffa5584ea
Toy model:
a family is either fertile or infertile, and fertility is hereditary
the modal fertile family can have up to 10 kids, the modal infertile family can only have 2 kids
in the olden days families aimed to have as many kids as they could
now families aim to have 2 kids each
Under this model, in the olden days we would find a high proportion of fertile people in the gene pool, but in the modern world we wouldn’t. Put differently, the old convention lead to a strong positive correlation between fertility and participation in the gene pool, and the new convention leads to 0 correlation. This removes the selective pressure on fertility, hence we should expect fertility to drop / infertility to rise.
Empirical evidence for this would be something like an analysis of the time series of family size variance and infertility—is lower variance followed by increased infertility?
How robust is the information that infertility rates are rising?
To be sure, I’m not an expert on the topic.
Declines in male fertility I think are regarded as real, though I haven’t examined the primary sources.
Regarding female fertility, this report from Norway outlines the trend that I vaguely thought was representative of most of the developed world over the last 100 years.
Female fertility is trickier to measure, since female fertility and age are strongly correlated, and women have been having kids later, so it’s important (and likely tricky) to disentangle this confounder from the data.