Total Fertility Rate (TFR) = number of children a woman gives birth to over her lifetime. Historically TFR's have hovered around 5-7 children per women. Almost everywhere in the world, as economic and technological development takes place, the TFR falls dramatically In some places it's higher, in some places significantly lower than that. The reasons for the variance are complicated and not well understood. This is called the "fertility transition." The United States went through its fertility transition early, and other than during the baby boom the TFR has hovered around 2 or below since the Great Depression: https://www.statista.com/statistics/1033027/fertility-rate-us-1800-2020/
This fertility transition is now in an advanced stage almost all around the world. In fact, some analysts are predicting that this year will be the first time (ever?) that the world as a whole has reached below-replacement fertility. The causes of fertility rates are complicated, multivariate, and above all poorly understood.
The future belongs to those who show up. So who IS having kids in America? Ethnically, Hispanic women have the most children, but their birthrates are crashing extremely rapidly as part of a greater phenomenon where the White and Hispanic populations are converging on several important factors. Black women have more children than White women and have for some time, which has allowed them to hold onto their historical 11-13% share of the population even as the non-hispanic white proportion of the country has dropped. But this fertility advantage is dwindling. Other than Asian women (who have rock bottom fertility rates of 1.1-1.3) all groups in the US are converging to around 1.7 children per women, or perhaps even lower than that.
Politically the question is more interesting. For women born in the 1970s, self identified conservative women had around 0.25 children than self identified liberal women. This is a meaningful, but relatively small difference. However, this is a lagging indicator. For women in their 30's, the gap is a lot larger but it's possible that liberal women will in their 30s will have more later births than conservative women. But take a look at fertility rates by state (yes, I know this is from Twitter but this account is a pretty reliable source): https://twitter.com/BirthGauge/status/1460983673491279883
Top 10 states: Red, Red, Red, Red, Red, Red, Red, Red, Red, Red.
Bottom 10 states (and DC): Blue, Blue, Blue, Blue, Blue, Blue, Bluish-purple, purple, Blue, purple.
Not everyone having children in red states are white conservatives (in the south especially many are minorities) and not all children from conservative households stay that way so I don't think this portends a long term and inevitable conservative dominance. But I think it is still a socially/politically relevant fact that white liberals seem to be going the way of the dodo bird, genetically speaking. If this groups wants to continue to hold onto its share it must do so through conversion.
What can't be denied is that clearly conservative areas are having more success at getting the youth to breed than liberal areas are. While this may provide conservatives a sense of smug satisfaction, this most likely has more to do with cost of living and urbanization rather than policy, as the "family values" party doesn't do all that much for families. But still, the numbers are what they are and liberals ignore this at their own peril. Anecdotally, I expect this trend to grow far stronger with the millennial's and gen-z. I am in my mid to late-20s right now, about the age that many of our parents had their firstborns, and the only people I know who have kids are conservative religious types. The people I know who are in a position to have kids in the next few years (stable relationship/married/engaged, economically secure, non-hedonistic) don't skew as conservative/religious but are far from leftist zealots. The most liberal people I knew from my youth are still status chasing in expensive big cities.
While it's true that kids from conservative families don't always stay that way I expect that 1) The people of my generation who have remained religious and conservative despite being run through the public school and social media ringer are far more likely to raise children who stay that way than their hapless boomer parents, and 2) Personality is extremely heritable, especially when the parents get an 18 year crack at the child's environment, so if conservatives are having far more children the countries culture and temperament will still change even if a large percentage of these children change ideologies.
I also wonder what is going to happen when the number of childless adults rises. Given the already fragile mental state of people in my generation, I'm not bullish on their personal happiness thirty years from now when their parents are dead and their families aren't growing. It really makes me sad.
Wildcards: The US is peppered with small religious groups with ultra high fertility rates. Most famously the Amish, but also Hasidic Jews, Hutterites, conservative Mennonites, and to a lesser extent Latin Mass Catholics, fundamentalist Mormons, and Quiverfull Evangelicals. It's the same principle as compound interest--given enough time, something that starts out small can grow extremely large, which is why the Amish, who numbered about 5,000 a century ago, aren't really that small an ethnic group anymore, now boasting 360,000 adherents. There's basically zero conversion, that's purely internal growth. Continuing that growth rate would yield 26 million Amish people in 2121. The Amish as a whole have a TFR of 5-6, but certain conservative sects have even more kids, 7-10 per woman and so are growing even faster. Hasidic Jews are going to be around 35-40% of children in Brooklyn in the next decade, and will reach majority status very quickly if trends don't change.
The past doesn't predict the future and the birthrates of these groups will eventually hit a wall....but when is anyone's guess, and what will happen afterward is unknown. Millions of ex-Amish and ex-Hasidic Jews filtering into mainstream society fifty to seventy five years from now is a political and social phenomenon no one is expecting but one that I believe is pretty much inevitable unless their TFR crashes to something resembling secular society very quickly.
Anyway I don't really have a point of this post. I was actually just jotting stuff down for my own purposes and thought maybe someone on this forum would find it interesting. I don't know what the future holds, but it's certainly interesting! If you're currently on the fence, you should have a kid.
