Natural Fertility: How many kids will a woman have in her lifetime?

If humans are ever put in a zoo by an alien race, and we are left to our own devices with plenty of food, medicine, exercise and safety, and with an ideology that neither shuns children or demands loads of them, how many children would women have?

Well it turns out researchers have been asking this question for a long time.
The Amish

I just read an interesting research paper called Population growth and fertility paterns in an Old Order Amish Settlement. by L. P. Greksa.

It looks at 1,337 Amish wives in the Geauga settlement in Ohio from 1908 - 1993. The Amish are considered an ultra high fertility group (in today's standards) straight out of the 19th century in their breeding habits, yet they use modern medicine. This makes them perfect for studying and looking at what the rest of society would look like if we still had traditional 'pro-fertility' attitudes. The conclusion of the paper says that the women do not attempt to control their fertility either up or down in any major way. To the researchers, this means the group in question is a "natural fertility population", which they desire to define so as to have a benchmark to measure from.

So how many babies do you think these perfect specimen, natural fertility, married Amish women have? Are they all like Michelle Duggar with 19 kids per woman?

Is it more than 19? Does it round down lower to around 10? (that was my guess). Let's see:

The mean number of pregnancies per married woman was 7.7 (SD 3.6). Fifty-two pregnancies terminated  in a stillbirth and 41 women gave birth to one set of twins, four gave birth to two sets of twins, and one woman gave birth to four sets of twins, for a twinning rate of 13.9 per 1000 pregnancies [1.4% -DM] resulting in a live birth. Mean completed marital fertility was 7.7 (SD 3.6) births, ranging from 0 to 17 births. About 3% of these women were childless while 28% had 10 or more births.

The men get married at 22.2 years, women at 21.1 years. The birth of the first child is consistently a year later when the woman is 22.1 years. The second child is consistently born 1.5 years after the first, with subsequent births spaced just under 2 years apart. For the period studied ('08-'93), the age of the last birth has dropped from age 40 to 35, marriage age and first birth age both dropped by one year, and spacing also dropped slightly. The fertility rate also dropped by 1 child during this time.

In this study, the 7.7 children per woman is per married woman, and I am unclear if this study ever actually says what the Total Fertility Rate for the community is. It does give data on sterile couples (3%), stillbirths and twins though. After all that is factored in, the number is still 7.7 per married woman, and of those with children the average is 7.94.

Normal Fertility Rate

So what does this all mean? Almost all of these numbers were different than I expected. I expected them to be marrying younger, having more kids for a longer time, and I expected the natural infertility to be higher. Instead the study shows that

 normal human women have a very reasonable 7.7 kids within a 14 year timespan.

The biggest family of all 1,337 of these women had 17 kids (so even Michelle Duggar would have a big family in this Amish community). And only 28% of families had 10 or more kids, with ony 3% of couples being infertile (way lower than I thought). Another fun fact is that the 7.7 "completed marital fertility rate" is not comparable to the "Total Fertility Rate" we are used to seeing. Total Fertility Rate includes all women of childbearing age, which will include singles who will never have kids such as nuns, the severely disabled, or those who otherwise have a vocation other than marriage.

If 30% of our study population remained unmarried and childless, the Total Fertility Rate would be still be 5.4 children per woman! That is three times the U.S. Total fertility rate!

My take away from this is just how incredibly... normal... and natural all these numbers seem. As a father of 5 myself, who can easily imagine more kids in my home, but find it harder to imagine having 10+ kids, I took comfort that 7 or 8 kids is naturally where fertility will end up (on average) for people in a healthy marriage. It is so easy to believe our culture that says having 3 or 4 kids is "a lot". Well it just isn't. In fact those 3 or 4 kids are 

below the average for where a couple will naturally be.


Our American TFR of 1.9 children per woman is now "well below" the replacement level of 2.1 needed to just keep a population steady. And much of that number is from new immigrants, who quickly adjust their fertility habits in the first and second generation, and anyway the countries who have been sending immigrants are no longer doing so and will soon stop. The American middle class is down to a TFR of 1.6 and falling.


I am not saying couples with zero or 1 or 2 kids should feel second class. Unless they have that few because they have an unhealthy view of children and their place in marriage. Obviously couples can be infertile (even 3% of Amish are), can have vocations or health issues which make it prudent to limit the number of kids, even to zero potentially. But these exceptions prove the rule that families should naturally be much larger than they are in our culture.

The exceptions that prove the rule.
Infertility.
3% infertile couples is... 3%. Get over it! That is a very small amount of couples! Yet if I had a nickel for every time I hear this as a reason why every family I see has only 1 or 2 kids, I could buy my own tropical island. Even factoring in infertility, the normal fertility rate for married women is still 7.7 kids

Insanity.
All parents have mental issues to some degree that having more kids may make worse. But are Amish women with 8 kids going insane by the truckload? I don't think so. Will having child number 4 really push most women over the edge? Or is it more likely that only a small percentage of parents have true psychiatric problems that make it unwise to have more kids? Even if I were generous and assumed that 30% (!!!) of women went clinically insane the day their third child was born, and never had another child, the Normal Married Fertility Rate would only drop by 1.41 kids per woman to 6.29.

Going to college extends time of marriage and first birth.
This is another very valid reason that a woman's fertility might be reduced. And using our Normal Married Fertility Rate of 7.7, with women becoming mothers at age 22.1, we could account for a generous 2 years of post college time to get married and conceive, and then she gives birth at age 24. That is a full six years after high school graduation, plenty of time for a college degree or two. So to account for this lost 2 years from her reproductive clock, lets deduct a full child from every woman in our study. That's right folks, we will assume universal college education from our women! They all lose one child and our average drops to 5.29.

Working outside the home. Some people say that families are so small because women have to work, and no longer have the time to give birth and to properly take care of lots of kids. To this I say... yep that is true. This is on the one hand a valid reason to reduce the number of kids you have, but at the same time is a bad excuse because it should not be happening nearly on the scale it is. Ask any woman to list the most fulfilling aspects of her life. If she has kids, she will have them higher on the list than a career. Yet the same woman will often say that her career is the reason she did not have more children. This makes no sense. If raising good human beings from childhood to adulthood is the most important job on earth, which we all agree that it is, then why do so many women choose something less fulfilling to fill their time? This one is hard to estimate, but my guess that in a healthy society no more than 30% of married women would want to work outside of the home in such a way as to reduce normal fertility. If these 30% each limited themselves to an average of 2 kids each, our average drops to 3.88 kids per married woman.

So assuming all the modern things we blame for our low fertility, we are still left with 3.88 kids per married woman in a healthy society.

Now let's take this society and assume that 20% of the women do not get married and become nuns or run businesses or whatever (20% seems like a lot by the way). After we factor that 20% in, we are still left with 3.1 as our total fertility rate. 3.1 is considered by demographers to be a high growth rate and significantly higher than the replacement rate of 2.1.
You might ask: Where the heck are you going with this you long winded weirdo?
Here is my point:
If we believe what our culture tells us, that it is perfectly fine that families come in all shapes, colors and sizes, and arrangements, with same sex parents or divorced parents, with any number of kids, with either mom or dad (or both) working and sending junior to the public school... if that is really true... and all that is just so *great* for families and we live in such a wonderful new springtime of humanity... then why do all the families I see buying into these modern notions look so much the same, with the same abnormally low number of kids (0-2), with most of the moms working outside the home and still doing the housework**, with 50% divorce rates?

Instead of being progressive and bold, our new culture is homogeneous and boring.

On a basic level using the simplest of math, think about it like this: Not every woman is called to marriage. And of those that do marry, I would argue that most married women will have various trials (described above) that prevent them from having lots of kids.
So if both of these things are true, and the replacement fertility rate is 2.1 children per woman in general, then how can we think that having 2 kids per married woman is healthy? Married people need to be having far more than 2.1 kids for a society to simply replace itself because they need to be having the kids to replace those who will not or cannot have them. As I have shown above, when we see a family with 3.88 kids we should be thinking "that is an average, healthy family size". And considering how conservative I was with my math (20% of women not marrying would be very high), we should consider the 3.88 to be on the low side.

So the next time you see a family with 4 or 5 kids, remember that that is a very average number. And a family with 8 kids should look no stranger to us than a family with only 1. We cannot let our suicidal culture dictate to us what a normal family size is. The simple, scientific fact is that a normal, healthy family size, even in the modern world with all its challenges, will be far larger than is culturally acceptable.


*If we were to translate the 7.7 married fertility rate into a Total Fertiltiy Rate, it can only go down because we are adding in non-breeding women. Let's pretend 10% of all Amish women never marry. If the married fertility is 7.7, then the total fertility would drop to 6.9. Married women would still have their 7.7 kids, but overall, the Total Fertility Rate would drop due to the 1 in 10 of all women that will never reproduce. If the number of unmarrieds rises to 30% of women in this population, the TFR drops to 5.4. If fully half of women in our naturally fertile society never marry and reproduce, then the total fertility rate drops to 3.85. 10-30% of women never marrying and procreating does not seem all that unreasonable. Particularly if marriage is seen as the important vocation it is, to not be entered into lightly. I think one thing that is perhaps not natural with our Amish case study is the high marriage rate, which I suspect is well over 95%. So although their family fertility is "natural", perhaps the number of families is unaturally high due to their anabaptist religion and a lack of vocational choice.


**The studies I read on European demographics last week had hard evidence of this. Unfortunately I cant recall where the data is located. But it was astounding how even in northern Europe, where women are supposedly so advanced in equality, they still do most of the housework.