For a site where the average user is familiarized with Big O notation, the HN hive sure has issues accepting that overconsumption and overpopulation are a fact.

Are they, though? Let's consider some facts.

Per World Bank data, the percentage of the global population living in extreme poverty (less than $1.90/day) has dropped from 44% to just 9% since 1980. In that time, the population has grown from 4.4B to 7.6B.

Speaking of population growth, it's down to 1.09%, the lowest since the numbers I'm looking at started being kept, in 1951. That's down about 50% from a high of 2.09% in 1968.

So two facts here. First, the population is leveling off. Second, even with the population growth over the past almost 40 years, billions of people have been lifted out of poverty. So the idea that overpopulation is making things worse is demonstrably, factually untrue.

The next stage of this argument would be one of overconsumption - that we are "destroying the planet", and this cannot be sustained. But what does that mean? Well, what if we run out of fossil fuels? (This is the one that worries me the most.) Currently, we are shifting rapidly to renewable sources. Even if they don't dominate, the curve is heading that way at logarithmic speed. Already, solar/wind are cheaper per kwh than coal or currently-cheap natural gas. As storage mechanisms become widespread, it seems like the grid will likely adapt from the current baseload + peak model to a wind/solar + storage model. That's clean decentralized, and (for now) limitless power.

Well, what about global warming? Yeah, it sucks, but. We can and will adjust. Even as oceans rise, they rise slowly enough to abandon unworkable structures and replace them with new ones on higher ground. Farming will adjust crops and techniques to changing climate. It's not impossible, just difficult.

What about habitat distruction and loss of biodiversity? Yeah, so? Again, this sucks... but it's mostly just unaesthetic. It doesn't truly harm the human population. It's not going to kill billions.

And remember what's driving this population growth - a massive increase in our odds of surviving as individuals, due to vaccination, sanitation, and education. Birth rates drop within a generation when a region develops modern sanitation and education. What we're seeing isn't an increase in birthrate, but rather an increase in survival rate. Birth rates are under control in most of the world today, but it will take half a century or more for the baby boom from the transition periods to die of old age.

So no, I'm not convinced that overconsumption and overpopulation are a fact.

I agree with everything you said, except the conclusion. Here's how I think an alien biologist would think about human demographics:

1. Below replacement fertility rates indicate that humans are facing some novel selective pressure to which we are poorly adapted. "Modern Life" is probably a useful label for this negative selective pressure.

2. The fact that there is high variance in reproductive outcomes in the developed world—and, specifically, that some women still have many children—indicates that some humans are already adapted to this novel selective pressure.

3. Because the variance in fertility rates between women is so high (some women have 0 children, while others have 4+), the adaptations which result in high fertility should spread throughout the entire population relatively quickly.

So, yeah, we don't have an overpopulation problem now. And we probably won't have one while you and I are alive. But the future of this planet is for it to be terraformed to support as much human life as possible. If we're smart we'll start thinking about how to make that future one where a high quality of life is possible.

Why is replacement fertility rate necessary? I do agree we are adapting to new evolutionary pressures (one of which is that children become an expensive burden rather than a source of family income), but I don't see a problem with the global population leveling off in a few generations, then shrinking by a billion or two.

I was thinking earlier about this birth rate in terms of generations. I'm 53. My paternal grandparents, living in rural poverty in Kentucky, had 13 children, of which 8 survived. None of those 8 had more than 4 children of their own. My grandfather, born in the 19th century, was illiterate and worked someone else's tobacco fields. My father went to high school and owned a blue-collar business. I went to college and work in software. My spouse is 47. Her maternal grandfather grew up in the Kansas Dust Bowl during the Depression, hunting squirrels after a day's work so his family could eat, and he went to bed hungry sometimes. He parlayed his WWII service into a Harvard MBA, and became a VP at Ernst and Young, retired a millionaire. He and his wife had 8 children, all of whom survived, because they were living much better than my father's family did. None of those 8 children had more than 3 children of their own, and some are childless. I have three siblings. None of us had more than two children. Of my two adult children, one will almost certainly be childless, the other I give a maybe 75% chance of children.

This is what happens to birth rates.

Iran, for example. In the early 1980s, the birth rate in Iran was over 5. Now, it's 1.6, lower than the USA or Europe. Iran isn't unusual. This happens everywhere that gets out of extreme poverty. And extreme poverty? That was my grandparents, in the US, in the 20th century. For the most part, such poverty no longer exists in the tobacco fields of southern Kentucky.

I don't think it's productive to speculate about a sudden sharp increase in birth rates over a century from now, based on conditions that are necessarily different from the conditions that are driving a drastic drop in the birth rate today. It's not really our problem, and we have no useful facts.

What we do know is that today, birth rates are plummeting worldwide, to below replacement level. As the last generations of population boom fade away over the course of the 21st century, it's unlikely to grow again. Barring unforeseeable changes, global population will likely shrink some over the 22nd century and then stabilize at whatever level of "terraform" is necessary.

By then, the era of fossil fuel will be over, and hopefully the atmosphere will start to stabilize. Humanity will be mostly on solar power, with sustainable agriculture feeding everyone. I believe that centuries from now, Earth will be a garden of Eden again, as the surplus resources get turned to making it beautiful, rather than just fending off starvation.

> I believe that centuries from now, Earth will be a garden of Eden again, as the surplus resources get turned to making it beautiful, rather than just fending off starvation.

All of human history up until the middle 1800s was spent at the malthusian limit: barely enough food to feed all the people. We are living through an aberration at the moment caused by a drastic increase in food production combined with a decline in birth rates. What I am saying is that birth rates will bounce back.

My family tree looks a lot like yours: lots of dead ends. My father has 6 siblings and my mother has 3, for a total of 11 siblings (including my parents). Collectively, all of those siblings would have to produce 20 offspring to maintain 0 population growth. But there are only 7 offspring in my generation. That represents a huge pruning of my lineage.

But.

All of the children in my generation are the offspring of parents who decided to have children in the age of birth control, women in the workforce, etc. And all of the children in the next generation will have gone through another round of intense selection. If you just play that out for a few generations, you're left with a population that has a really strong pedigree for fertility in the face of Modern Life.

You might think this is no big deal, but I can tell you that there are people out there who have a really strong innate drive to have children. I am one of them. So is my wife. We'll start working on our 4th child next year. All of the other people we know with 3+ children have markedly different personalities from the people we know with 2 or less.

Once resistance to modern life starts to gain prevalence in the population, it will spread incredibly rapidly. Take a look at the Haredi Jews in Israel. In 1990, they represented 5% of the Jewish population in Israel. Now, 30 years later, they account for roughly 30% of the Jewish population under 20. What happens when you play that process out for another 30 years? I'll tell you: what happens is that the Haredi are the Jews in Israel.

The same thing will happen with high fertility people in the rest of the developed world. You're just not seeing it because your vantage point is from a part of the tree of life that is being pruned. But there are parts of the population that you're not exposed to. They're religious and conservative and hard to notice because they're too busy raising children to be visible on social media and in high culture. But they're there.

> They're religious and conservative and hard to notice because they're too busy raising children to be visible on social media and in high culture. But

The thing is that they are quite visible, and quite a fair share of the people that are now in the group choosing to reproduce at or below replacement rates, either strategically or just by deprioritized reproduction cookies to career, etc, so that it is delayed come from those backgrounds. Biological decent doesn't dictate personal choice.

Or to put this another way... I think it's far more likely that modernism will doom high birth rate, impoverished religious cults, than it is that high birth rate impoverished religious cults will doom modernity.

I see what you're saying, but that only works if the process is continuous - if the religious culture that values high birth rates continues for several generations. For a counterexample, look at Saudi Arabia, another religion-driven state. In 1960, the birth rate was 7.22. Today, it is 2.58. So religious parents have 8 children, and all 8 survive, because it's the 21st century and they're getting vaccinated and not drinking their neighbors' poo anymore. Will all 8 of those children go on to have big families of their own, in keeping with their religious sect's values? Or will they move to town, get better jobs, and start using family planning to have a family they can afford, knowing their children aren't going to die of cholera or smallpox or simple starvation?

Interestingly, I did some googling on the Haredim. As of 2010, the poverty rate for the Haredim in Israel was 60%, far higher than the rest of Israel's Jewish population (probably more in line with the occupied Palestinians, who also have a very high birth rate). Population size or not, this is extremely limiting for their political power. Money counts for a great deal. If they can't afford to expand their communities, and refuse to participate in the broader economy, they'll necessarily be limited in their growth.

So no, I'm not concerned about this problem. Religious groups that refuse to participate in mainstream society may have high birth rates, but will also have high poverty rates. And I see no evidence at all of this behavior in American society, outside of tiny cults. Even the Mormons, probably the best and largest analogy, have seen their birth rate drop drastically, falling 18% from 2007 to 2014 alone. I'm not expecting the LDS church to overrun the nation anytime soon.