Will Fertility Rebound? New Study Says Yes

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The conventional wisdom is this:  just as birthrates have plunged in places like Europe, so, too, will they drop to replacement level in Africa, and, in any country in which fertility rates have dropped, it’ll be necessary to offer financial inducements like parental leave benefits and child benefits to bring birthrates up, as well as increase immigration levels as needed.

A new study suggests that this conventional wisdom is wrong, and that birthrates will rise again, for a surprising (or perhaps not-so-surprising) reason: evolution.  The article’s title is self-explanatory:  “The heritability of fertility makes world population stabilization unlikely in the foreseeable future.”  It was published in the journal Evolution & Human Behavior, but a summary of the argument is available at the Institute for Family Studies blog, and one of the two authors, Jason Collins, also provides some data in his own blogpost (he co-wrote with Lionel Page).

The core idea is this:

As long as a society has no practical means of controlling its fertility, fertility itself is not particularly heritable.  Yes, at the margins, couples who are marginally fertile will have fewer kids than those who do not have any such issues, but this isn’t going to make a significant difference in fertility rates over time.

However, as soon as individuals exercise choice over how many children they wish to have, then fertility does become heritable; that is, some constellation of traits that affect how many children one chooses to have are genetic as opposed to simply the product of the environment.  This might be as simple as a genetic predisposition to “liking children” or a disposition towards being religious, or might be a personality that is better able to cope with the chaos of a large family or regimented enough to reduce the chaos, or less anxious about financial strain or less keen on world travel.  It might be a genetic predisposition towards finding Mr./Ms. Right early rather than waiting until age 30 or later.

The paper is actually agnostic on what the specific mechanism for the heritability of fertility might be, just that the math checks out, based on the types of calculations that researchers use to identify the degree to which some characteristic or another is heritable.  And based on these mathematical models, they determine that once, in any particular region, fertility is low enough that individual choices begin to make a significant difference in family size, fertility rates will begin to rebound, because the parents who are predisposed to having above-average numbers of kids will pass on those traits.  They calculate that the world fertility rate, which now stands at 2.52 (as of the period 2010 – 2015) and is forecast to drop to 1.83 in 2095 – 2100 in the baseline UN forecast, will, in fact, continue to drop, but eventually, as this evolutionary impact comes into play, birth rates will rebound to slightly above replacement level, at 2.21.  At a regional level, European fertility rate is forecast to reach 2.46 instead of 1.83, and North American fertility, 2.67 rather than 1.85.

To be sure, inherent desires for a given number of children and ability, or lack thereof, to control one’s fertility, are not the only factors influencing a country’s fertility rate.  Just as important in determining a country’s fertility rate are economic conditions and norms within the broader culture — whether a baby boom in which women without deeply maternal desires feel pressure to have children or, in current conditions, when women are outsiders, and possibly even shamed, for having an above average number of children.  But Collins’ and Page’s premise is that, even within a given set of economic and cultural circumstances that produces generally low fertility, genetically-influenced differences in personality will, to at least some extent, produce long-term fertility increases.

Ultimately, neither laypeople nor scholars can know the future with any certainty.  It’s easy to find predictions of a Star Trek-like utopia in which no one needs to work but merely does so for reasons of personal fulfillment, or predictions of a dystopia in which the rich oppress the poor, who live in squalor.   While this analysis doesn’t prove anything one way or the other, it’s a very interesting piece of the puzzle.

What do you think?  Visit JaneTheActuary.com to leave a comment!

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