It is folk wisdom in certain circles that having children is just about the worst damage a person can inflict on the environment. There is an appealing logic to this idea: people consume a huge amount of natural resources, so a world with less people will result in less pressure on already strained ecosystems. Therefore, the thinking goes, having less children than you would otherwise—or abstaining from having children at all—is one of the most important choices a person can make about their impact on the environment.

At a basic level, this analysis makes sense. People—especially people in the developed world—consume a tremendous amount of resources. Having less people in the world would ease pressure on natural ecosystems. And, at a personal level, having less children would contribute to easing this pressure. There is no logical flaw in this analysis; it is all sound reasoning.

But it is incomplete.

It examines only the choices of a single couple. The problem, though, is that other people exist. And, as a result of not considering the bigger picture, this analysis comes to precisely the wrong conclusion. Which is a shame, because this line of thinking appears to hold a lot of sway with certain people. So much so that I have encountered people who have taken it to heart and are having fewer or no children as a result. The truth, though, is that if you are concerned about the environment, you should have children. Lots of them.

Let me explain myself.

At the most fundamental level, the reason that any organism exists is to reproduce. Reproduction is the defining feature of life. About 4 billion years ago, some complicated molecules started making copies of themselves. Then variations arose which were better at making copies of themselves. Further variations arose which improved their reproductive rate even more. And so on until we got the world we live in today, teaming with life, all of it oriented toward one singular purpose: reproduction.

Humans are no exception. We often lose sight of this fact because our lives are filled with such a richness of experience. But when you dig into all of that richness, it turns out that it’s actually all related to reproduction. It’s hard to see that, though, because we live pretty long lives and only have a few children, so most of our experiences are pretty far removed from the basic mechanics of sex and childbirth. But it’s ultimately all about reproduction.

The result of all this copying is that any given species will multiply until it saturates its ecological niche. An ecological niche is the way that a species makes it’s way in the world. So, the ecological niche of trees is to grow really tall and harvest sunlight. Birds, on the other hand, have a very different ecological niche: they fly around and find food sources in their environment. And bees have a very specialized ecological niche: flowers give them pollen as payment for enabling flowers to fertilize each other.

Each of these ecological niches, or ways of making it in the world, will only support a population of a certain size. There is a lot of land in the world that can support trees, but it’s not infinite. And that finite area of land determines the number of trees that can exist. Things are the same with the birds and the bees: there are only so many worms and so many flowers for each, respectively, to dine on. Now, some years may be better than others and the population of a species will expand or contract in response. But whenever an ecological niche has additional carrying capacity, it quickly gets used up.

And I do mean quickly.

Many species of animals produce hundreds or thousands of offspring for each mating pair of adults. Even among mammals, it is common to produce a handful of offspring each year. Since each mating pair of animals only needs to produce two offspring in their entire lifespan to maintain a stable population, this means there are essentially always extra offspring desperately trying to eke out a place in that ecological niche. So when there’s excess capacity, it gets filled.

It takes a pretty long time for humans to produce offspring, so you might think that humans are exempt from this dynamic, but we’re not. It does take us a little longer to grow our population in response to additional carrying capacity in our ecological niche, so we don’t swarm like locusts or rodents, but human populations can grow shockingly fast.

Here’s a thought experiment that you can easily replicate on a calculator: start with one breeding pair of humans and assume that each couple has four children (so the population doubles each generation). Then figure out how many generations it takes to get from one pair of humans to the roughly 7 billion who currently inhabit the earth. You’ll find that it only takes 33 generations. If you assume that each generation averages 30 years (so, 2 children born before the mother turns 30 and 2 children born after), that means you get from Adam and Eve to 7 billion people in less than 1000 years.

So, you can voluntarily decide to abstain from having children, but that doesn’t mean that other people will follow suit. In fact, to the contrary, evolution will rapidly weed out any tendency to abstain from having children. As a result, choosing to have few or no children will have a relatively small initial effect, but then as time goes on, the only people left will be the descendants of people who have no inclination to voluntarily forego reproduction. And they will do what life has always done: reproduce.

And then we’re back at square one.

The key to arriving at a useful course of action on this issue is accepting that you, as an individual, are powerless to control the total quantity of humans that exist, because the world will just get filled up with the descendants of other people. But you can influence the proportion of humans who think like you and share your values. And the way to do this is by having children, because your children share whatever genetic inclination you have toward environmentalism, plus they will possess whatever values you instill in them.

I anticipate that the logic of this may be a bitter pill to swallow. Strain on natural resources is an important issue—possibly the most important long term issue that we face as a species—and the thought that there is nothing that can be done to influence the total quantity of humans might be demoralizing. But the thing is that the total quantity of humans alive can be influenced. Just not by you as an individual.

Instead, it is an issue which will require collective action. At some point we—humanity as a whole—will need to act collectively to prevent over-consumption of the natural resources provided to us by this, our only home in the vastness that is the universe. It will be one hell of an undertaking; so far we haven’t demonstrated any particular talent at species-wise governance.

Ultimately, to make progress on environmental issues, people are required. People to make phone calls, people to write letters, people to post and share on social media, and, most importantly, people to vote. And because people are required, progress on environmentalism will be proportional to the number of people who care about it as an issue. So the winning strategy cannot be to choose to have no children. Because to do so is to actively contribute to a future where there are less people who care about humanity’s impact on the environment.

So have some kids.

Shoot for two. And if you take a liking to it, have a whole bunch.

A note before I continue: what follows is not an argument against abortion, which is a complicated topic. It is merely an argument against one specific idea that often comes up in the context of abortion.

I have sometimes come across the sentiment that it is better that a child not be born than that they experience a life of misery and hardship. Usually I have encountered this line of thinking in support of a woman’s right to terminate her pregnancy. But I have also encountered it in other places. For instance, it is sometimes expressed by people who have decided not to have children because they are concerned about climate change or some other catastrophe. I think it’s actually pretty easy to show that this line of reasoning is flawed.

Perhaps you will agree with me.

The first flaw in this line of reasoning is that the person doing the evaluation is looking at a quality of life which is significantly worse than the standards which they hold for themselves and then deciding that it is unacceptable to let children experience such a degraded quality of life. But that is the wrong comparison to make. Unborn children do not have a choice between a sub-optimal quality of life and what you and I deem to be an acceptable quality of life. Instead, their options are between a sub-optimal quality of life and no life at all.

So, to determine whether it’s good for them to be brought into a difficult and challenging life, we need to determine whether people who have difficult and challenging lives think that their lives are worth living. This might seem like an impossible thing to determine, but it’s actually quite simple, because remaining alive is optional. Almost every single person has the ability to take their own life if they decide that it is not worth living.

When you look at life that way—as optional—it is kind of amazing that, despite the tragedy and hardship which pervades many people’s lives, very few people commit suicide. The annual suicide rate is about 13 people out of every 100,000, which, according to my back of the envelope calculations, works out to a lifetime suicide rate of about 1% at most. Of course, that number is tragically high, but I think the fact that 99 out of 100 people choose life, despite all its difficulties, speaks to how fundamentally worthwhile being alive is.

Now, I could probably rest my case there. After all, it’s hard to argue that a difficult life isn’t worth living when basically everybody who has a difficult life demonstrates that it is worth living by opting to continue living it. But we can take this analysis even further.

As difficult as life can be, most people—even people who are born into circumstances which we all agree are terrible—have lives that are immensely better than those experienced by certain groups of people in the past. I think you will agree that being an American slave or a prisoner in a Nazi concentration camp is about as bad as life can get. Prisoners in concentration camps were stripped of their possessions, starved, forced to perform grueling labor, and had to go through each day with the knowledge that their eventual fate was probably death. American slaves didn’t have it much better. They were beaten, raped, and tortured; families were routinely torn apart; and they lived every day with the knowledge that they and their children would probably die as slaves.

Life doesn’t get much worse than that.

And yet, while it is hard to determine what the suicide rate was among these groups, it is safe to say that many of these people decided that their lives were worth living. After all, most the roughly 40 million black Americans alive today are descended from people who chose to persevere through the living nightmare of slavery. And, if you look at pictures of the Nazi concentration camps being liberated, every single emaciated prisoner that you see looking at the camera is someone who chose to persist through the hell that had been their daily life up until that moment.

I think it is useful to keep these extreme examples in mind when deciding just how worthwhile being alive is. Because if a slave or a prisoner in a concentration camp opts to continue being alive, then, in almost every situation people in the developed world face today, the scales are tipped so far in favor of life being worth living. As tragic as it is to grow up without a father, or in an abusive home, it is so much better than the worst that life can be. And life at its worst is still worth living.

So, if you think a child not being born is a better alternative than that child growing up in unfortunate circumstances, or if you think it would be better to spare your children the possibility of living in a dangerous and uncertain future, hopefully these arguments will make you reconsider. And, anyway, who are we to decide if another person’s life is worth living? If you consider that question seriously, I think you will have no choice but to agree that we should defer to others when it comes to measuring the worth of their lives. After all, they can always opt out if they find it lacking.

But I bet they’ll choose life.

If you're reading this, then chances are that your way of life is default dead. Now, that's a hell of a thing for me to say to you, given that I probably don't know much about you, so let me elaborate a bit and I think you'll come to see that the logic of what I'm saying is inescapable.

We'll start with default dead.

Default dead is a term coined by Paul Graham, a venture capitalist, to describe the state of some of the startups in which he has invested. The nature of startups is that they begin with a rudimentary product, very little money, and, at most, a handful of customers. Then they borrow money from venture capitalists like Mr. Graham in the hopes that they can hire employees, get their product to market and, eventually, acquire customers.

It's the 'eventually' in that last sentence where the concept of default dead arises. Because venture capitalists will only lend a startup so much money. And if a startup has hired a bunch of employees, then the money they've borrowed will eventually run out. This is the point Mr. Graham makes in his essay: if things continue as they are—if a startup keeps spending money and adding customers at its current rate—will it run out of money before it's able to bring on enough customers to become profitable? Or, in other words, does continuing on its current trajectory mean that the startup is default alive or default dead?

This question is important, because, if you're default dead, nothing else matters. There is a ticking clock which is counting down the time until you go out of business. The only thing you should be focused on is getting yourself to a position where you are default alive. And Mr. Graham points out that borrowing more money is not a viable fallback strategy, because, paradoxically, the more desperately you need the money, the less willing people will be to lend it to you.

But enough of venture capital and the world of startups, because this concept is applicable on a much larger scale. Essentially, if you're from the developed world, and you're not super religious, then your way of life—your culture—is probably default dead. That is, if things continue on their current trajectory, your way of life will eventually cease to exist.

The reason that this is the case comes down to demographics. Specifically, it comes down to the replacement fertility rate, which is the number of children each woman must have in order to prevent the population from decreasing. In the developed world, the replacement fertility rate is 2.1 children per woman (the .1 is to account for people who die before the end of their fertile life). And keep in mind that this number is an average, so if some women are having 0 or 1 children, then there need to be enough other women who are having 3+ children to get the average to work out to 2.1 children per woman.

If the fertility rate of a culture drops below this number, then it will start shrinking. If it rises above this number, then it will grow. Or, restated in terms of our earlier discussion: if the fertility rate in a given culture is 2.1 children per woman or higher, then that culture is default alive. But if it's below 2.1 children per women—and it stays below that level—then that culture will eventually cease to exist: it is default dead.

Now, fertility rates are usually discussed in the context of nations. And, conveniently, nations are also a way you can define cultural boundaries. That is, we can speak of Japanese or French culture. So, we can look at the fertility rates of various countries to see if the cultures they embody are default alive or default dead:

A world map showing countries by fertility rate, according to The CIA World FactBook, 2015 estimates. Image by Supaman89 via Wikipedia, CC BY-SA 3.0.

Everything in blue has below replacement fertility rates. That covers basically all of North America and Europe, plus a sizable share of the developing world, including China, Russia, and Brazil. Essentially, the different cultures embodied by all of these countries are default dead. Now, China has over a billion people, so Chinese culture is not in danger of disappearing anytime soon. But there are lots of European countries with less than 10 million people, some of which already have shrinking populations.

National boundaries are not the only criteria by which a culture can be defined. Neighborhoods, cities, regions, political affiliations, religions, ethnic groups, and socio-economic classes all have their own unique cultures. And if you go digging, you can probably pull up fertility rates for many of these. I'll leave that to you, though, because what I really want to do here is get you to use this lens to look at your own culture.

So, think about the culture you identify with—whatever group you consider your people. This could be the culture of your country or religion, or it could be more specific than that: perhaps your people are well educated, secular and left-leaning, Or maybe they're working class religious fundamentalists. It doesn't matter; just whoever you think of as your people. Now take a look around. If the norm amongst your people is for most couples to have 2 or 3 children, with only a few having less than that, then your culture is probably default alive. But, if that's not the case, if, instead, most families in your culture have 1 or 2 children—or none at all—then your culture is default dead.

Now, the solution to the fertility issue which is usually put forward is immigration. At the national level, this means importing people from other countries. For cultures defined by criteria other than national boundaries—religions, socio-economic classes, political affiliations, etc.—this means recruiting people from outside of the culture. Immigration is a fine strategy, in general. And I am always happy to have more people think or believe like me. But immigration should never be the only strategy.

To return to our earlier talk of startups: a culture relying on immigration to make up for its fertility problem is like a startup borrowing money to make up for the fact that it isn't profitable. The problem is twofold: 1) neither strategy actually solves the underlying issue, and 2) both strategies are completely dependent on external circumstances to remain viable. In the same way that venture capitalists may decide to stop lending money to a startup, one day the rest of the world might not have any extra people for your culture to import.

And then what?

Now, I can't know what's going on in your head right now. But I can imagine there's a pretty good chance that you think I've been wagging a finger at you this whole time, condescending to you about how your culture is dying. But the truth is: I am pointing out that your culture is default dead because it is a convenient way for me to make a point. You see, if you are reading this, there's a pretty good chance that your culture is my culture. And my culture is default dead.

I look around at the kids I grew up and went to school with and very few of them have children. The same is true of the peers I am currently surrounded with. And yet they—we—are all getting to a point where having children is becoming a now-or-never kind of a thing. The story is the same in my family. Between my parents, there are 9 siblings. Those 9 siblings would need to have 17 children for their way of life to be default alive. But there are only 7 children in my generation.

Now, you might not think this whole default dead thing is a big deal. But I do. And, if you're at all concerned about how the future will play out—whether you care about climate change, civil rights, universal healthcare, space exploration, animal welfare, religious freedom, or gun rights—if you think that your worldview is correct and that more people should share it, then you should care about whether or not your people are having kids. Because the path taken on these issues will be largely determined by which culture has the most people. And if your culture isn't producing children, then how can it expect to have a say in the future?

I have come across quite a few people lately who are convinced that eating meat or dairy is bad for the environment. The logic behind this idea is that meat has an outsized environmental impact relative to the calories and nutrition that it provides. And the implicit conclusion is that a more plant based diet is good for the environment.

But thinking about the environmental impact of food in this way—meat is bad, plants are good—is useless. Many of the foods which these people probably think are great for the environment—basically all fruits and vegetables and especially kale, that icon of conscientious eating—are worse for the environment than meat. Usually much worse. Understanding the environmental impact of the food you eat is actually pretty straightforward. It mostly comes down to a simple rule of thumb:

The more a food costs per calorie, the worse it is for the environment.

To understand the logic behind this, first let's talk about some of the things that go into making the food we eat. We’ll start with plant based food. Broadly speaking, the ingredients are:

• Land to grow the plants on
• Water and fertilizer to feed the plants
• Pesticides to increase yields
• Labor and equipment to plant, harvest, process, and transport the crops
• Fuel to run the equipment

Then, for meat, all of these same ingredients are required as a baseline, since animals eat plants to grow, plus we need some additional in each category to raise, slaughter, pack, and transport the animal. There are probably a few things that I'm leaving out, but that's okay, because this covers most of it and we're aiming for a rule of thumb here, not a dissertation on agricultural inputs.

Now, let's think about what happens if, for some reason, we need to use more of one of these ingredients to make the same amount of food. Obviously, the cost to produce that food goes up, too. Right?

Maybe that's not so obvious, so let's go through a hypothetical scenario. Imagine that we have a kale farm and it takes the following to produce 1,000 bunches of kale:

• 1 acre of land
• 10,000 gallons of water
• 500 lbs of fertilizer
• 50 lbs of pesticides
• 200 hours of labor
• 100 gallons of fuel
• 20 hours of tractor time

Now let's see what happens as the amount of each ingredient that we need increases. Remember, this is a hypothetical situation; I have no idea how much of each of these inputs is actually required to grow 1,000 bunches of kale. But that's okay, because we don't care about the actual amount of raw ingredients required. We only care about the relationship between the cost of food and the amount of raw ingredients required to produce it.

For water, fertilizer, pesticides, labor, and fuel, it's rather obvious what happens if you need more of these to grow the same amount of kale: the cost to produce the kale goes up. If you need twice as much fertilizer, you'll have to spend twice as much on fertilizer. There's no getting around this, since you have to buy all of these items.

Land is a little bit more complicated. Let's imagine that, for some reason, it now takes 2 acres of land to grow 1,000 bunches of kale, instead of 1 acre. What happens to the cost to grow kale? Well, even if you already own the extra acre, it could have been used to grow a different crop, so the income that gets left aside as a result of not growing an acre of that other crop gets factored into the cost to grow the 1,000 bunches of kale. And if you didn't already own the land, you would have to buy or lease it. So, if land use goes up, cost goes up.

Tractor time is also a little bit more complicated. You could make the argument that a little more tractor time doesn't matter, since you already own the tractor. But it does matter. The useful life of heavy equipment is typically measured in hours of operation. So if you need more tractor time to grow those 1,000 heads of kale, you're using more of the tractor’s useful life. You may not pay the price now, but it's a real cost nonetheless.

Hopefully I've made a good case for the idea that, as the amount of raw ingredients required to produce a given food increase, so does the cost. Now I am going to make the case that the most important driver behind how much it costs to buy a food at the grocery store is the amount of raw ingredients required to produce that food. To do that, we will consider another hypothetical scenario.

Imagine you're a farmer and you've found a sweet niche selling an heirloom variety of eggplant. No other farmers are growing it, but it's a hit with consumers. As a result, you're able to sell these eggplants at a relatively high price. But a competing farmer notices that these eggplants are popular, does some calculations on expected yields, and figures out that you've got a pretty good thing going. The next season, your competitor also plants some of this heirloom eggplant variety. Now, grocery stores have two sources for these eggplants, so they're able to negotiate better prices from you. As a result, this heirloom eggplant variety goes from being abnormally profitable for you to just normally profitable.

This sucks for you, but welcome to the basic process of supply and demand under a free market economy; if there are markets or products which are unusually profitable, soon there will be competitors chasing after those profits and driving prices down in the process. Eventually prices reach an equilibrium that consists of the cost of production plus a reasonable amount of profit for engaging in the risk of running a business.

There are definitely exceptions to this, but farming and groceries are not them. It's just too easy for a grocery store to replace an expensive grower with a cheaper one. And it's just as easy for most consumers to shop at at whichever grocery store has the lowest prices. If you don't believe me, read the financial statements of huge grocery companies like Kroger or Safeway. Their margins are shockingly low.

So, the price you pay for kale at the grocery store is primarily a reflection of how much it cost to produce that kale. And how much it cost to produce is really just shorthand for how much land, water, fertilizer, pesticides, labor, fuel, and equipment went into making it. And the amount of land, water, fertilizer, pesticides, labor, fuel, and equipment that went into making it sounds an awful lot like its environmental impact.

But, in case you think I just pulled a fast one on you, let's consider each of these in turn:

• Land used for agriculture is unavailable for wildlife.
• Water used in agriculture is unavailable to support wildlife.
• Fertilizer is either extracted from the environment or requires an energy intensive process to produce.
• Pesticides inevitably end up contaminating the environment surrounding agricultural areas (just ask your local anti-GMO type for an earful on the topic).
• Labor is people and all the food, fuel, and stuff that people consume definitely has an environmental impact.
• Fuel extraction has a large environmental impact, as does the pollution that results from burning fuel.
• Equipment manufacturing uses lots of energy and raw materials.

So the price of food is a rough indicator of its environmental impact. $2 of ground beef has twice the environmental impact as $1 of ground beef. $1 of chicken and $1 of kale have roughly the same impact. And $2 of ground beef has roughly twice the impact as $1 of kale. I say roughly because kale might require more land and fertilizer, whereas ground beef might require more labor and equipment, and those things are not exactly equivalent, but, again, we're going for a rule of thumb here.

Now, here's the important part:

One dollar’s worth of kale, ground beef, and chicken might have roughly the same environmental impact, but they do not provide the same amount of calories.

In fact, it's not even close. Here is a graph showing the number of calories that $1 buys when spent on kale, ground beef, and chicken (darker). It also includes a few common staples for some perspective (lighter).

Prices were gathered from my local Fred Meyer in August, 2016. You can also check out an expanded chart which includes most common food items or the spreadsheet which the charts in this essay are based on.

This table really gets to the title of this article: kale is terrible for the environment. You can see it way down at the bottom of the chart, providing a mere 70 calories per $1. That’s 5x less calories per dollar than ground beef and 18x less than a whole chicken. Or, put differently, the environmental impact of a calorie of kale is roughly 5x greater than a calorie of ground beef and 18x greater than a calorie of chicken.

So, if your goal is to signal your virtue to your peer group—especially if your peer group is well educated, upper middle class white people—then kale probably can’t be beat. But if your goal is to minimize the environmental impact of the food you eat, then kale is a terrible choice. Just like pretty much every other fruit and vegetable.

Here’s a chart which shows the range of calories per $1 that each major food group provides:

Prices were gathered from my local Fred Meyer in August, 2016. You can also check out an expanded chart which includes most common food items or the spreadsheet which the charts in this essay are based on.

It’s plainly obvious that, of all the major food groups, fruits and vegetables have among the highest environmental impact per calorie. So, when I hear people saying that they are eating less meat because they want to reduce their environmental impact, all I hear is somebody who doesn't really know what they're talking about. Because when it comes to the environmental impact of your diet, what matters is the size of your monthly grocery bill, not whether your food came from plants or animals.

So if you give up eating meat, but your grocery bill is the same because you’re eating lots of salads and kale smoothies, then you haven’t really done the environment any good. Instead, you should be focused on shifting your diet away from high cost per calorie foods. So, more chicken, eggs & dairy (400–1200 cal/$), less seafood and steak (50–150 cal/$). More apples and bananas (200–600 cal/$), less blueberries and raspberries (35–65 cal/$). Include a grain or starch (1400–3000 cal/$) as a significant portion of most meals, cook with lots of butter and oil (900–5300 cal/$), and treat fruits and vegetables not as staples, but as what they really are: delicacies.

Now, since you’ve made it this far, I encourage you to take this rule of thumb and use it as a lens to look at the world around you. For instance, what does it imply about the environmental impact of:

• Organic vs. non-organic food
• Artisanal, locally grown vs. factory farmed food
• Eating at restaurants vs. preparing your own meals

And this rule of thumb is not limited to food; it can be applied to all of your buying decisions.

I'll leave that discussion for another time and stop here, though.

Caveats and Limitations

Being a rule of thumb and not a rigorous scientific methodology, this way of quantifying the environmental impact of the food you eat has some limitations:

1. It doesn't take into account externalities that occur while producing food. An externality is a cost which is external to the person or company that produces something. So, when runoff from a farm pollutes a river, that is an externality, because the cost of that pollution is borne by people in the community instead of by the farm. The big externality that probably comes to mind if you’re of the anti-meat mindset is methane emissions from cattle.

2. It doesn't account for preferences you might have about different kinds of environmental impacts. You might care a lot about land use, but very little about labor or capital costs. Or vice versa. But this method boils all of those very different environmental impacts down into one opaque number. If you want to get specific, you'll have to do some research.

3. It is probably not very useful across different time periods. The price of an input is a reflection of its relative scarcity at a given point in time and my intuition tells me that this can shift in strange ways over time. So, it's useful to compare the cost per calorie of apples to rice, but not useful to compare the cost per calorie of apples today to apples two years ago. In practice, I don’t think this limitation comes into play very often.

4. It probably doesn't work very well across national boundaries. If you were comparing the cost per calorie of kale produced in Brazil vs. kale produced in the United States, it probably wouldn’t be a very useful comparison. Kale produced in Brazil would probably have a similar environmental impact to kale produced in the U.S., but it would probably cost much less because Brazil is less developed. Again, though, the purpose of this rule of thumb is to help you make decisions about what you eat, and this limitation doesn't affect that.

5. The cost of fuel is not necessarily related to its environmental impact. As an example, imagine that the fuel cost in a head of kale comes to $0.10. If the price of oil gets cut in half (as it has in the last several years), then the cost of head of kale goes down by $0.05, even though the environmental impact of producing that head of kale stays exactly the same.

6. Finally, some people give up eating meat because they have a moral objection to eating animals. I will readily admit that the calories found in $1 worth of beef is not really a good way to measure the welfare of the cow that it came from.

Thanks to Monika Radon-Jones and Guru Khalsa for reading drafts of this essay.

In our day and age, it is easy to lose faith in humanity. It is easy to learn of the latest atrocity or injustice and decide that humanity's moral worth doesn't amount to much. And it is easy, once you find yourself in a mindset like this, to become alienated from your fellow humans.

But that would be folly.

Humanity is fundamentally good. That this is true comes down to a simple observation: despite all of the evil which we have perpetrated against one another, the human condition keeps getting better.

For millennia, our instinct to build things up has overcome our instinct to tear them down. There have been missteps along the way, and there is much work left to be done, but the overall trend is unmistakeable: throughout the world, life is getting better. Every single kind of violence is in retreat. People live longer. They have more economic opportunities and a greater say in how they are governed. And more people than ever before are now free to pursue that ultimate luxury: a life of purpose and contentment.

The good in us is so powerful that it has done more than just balance out our destructive tendencies. It has advanced our species from hunter-gatherers to a global civilization which has largely put down its swords and picked up the mantle of human rights. A civilization whose technological progress has made the necessities of life—food, water, shelter, and safety—abundantly available for vast swathes of humanity. And the good within us has accomplished this in the midst of all of our evil.

I cannot think of a higher testament to our worth.

Additional Reading:

1. A History of Violence, by Steven Pinker. Based on his book, The Better Angels of Our Nature, this lecture outlines the incredible decline in violence since the beginning of recorded history. Includes video + text transcript.

2. The Universal Declaration of Human Rights, adopted by the United Nations. I think it says a lot about us that almost every country on Earth — collectively representing most of humanity — acknowledges and agrees with the fundamental human rights laid out in this document.

Thanks to Guru Khalsa for reading early drafts and providing feedback.

Most secular people I know would probably be alarmed by the idea of a future in which the human race is highly religious. And they would also probably find it highly unlikely. Indeed, I have occasionally heard a sentiment expressed by secular people that goes something like this: the beliefs of most religions are so preposterous that humanity will obviously become less religious as our knowledge and understanding expands.

When I encounter this sentiment, my response to the person expressing it is always the same: How many secular people do you know with big families? Inevitably, the answer is always the same:

None.

I ask this question because the logic of the matter is inescapable: the human race of the future will be composed of the descendants of whoever breeds the most.

That religious people have more children than non-religious people cannot be argued. Worldwide, the difference is staggering. According to a report by the Pew Research Center, people who are unaffiliated with any religion have 1.7 children per woman, well below the replacement fertility rate of 2.1 children per woman. In comparison, Christians and Muslims—the two largest religions, at a combined 54% of the world population—have 2.7 and 3.1 children per woman, respectively.

What can be argued, though, is whether religious people have more children because they are religious, or if there is some other factor which causes people to both be more religious and have more children.

Some other factor like, say, poverty.

Intuitively, poverty as a driver of both fertility and religiosity makes a lot of sense. Worldwide, there is a clear link between how developed a country is and it's fertility rate. And there is also a clear link between how developed a country is and how religious it's people are. Indeed, the largest driver of currently high Christian and Muslim fertility levels is the fact that they are the predominant religions in sub-Saharan Africa, which is one of the least developed regions in the world.

A common assumption, then, is that the rest of the world will also become less religious and enter a similar demographic transition—to much reduced fertility—as it becomes more developed. And this seems like a reasonable assumption; ultimately we're all just human. It is interesting, though, to consider what happens to a population once the process of demographic transition has kicked in.

Because it turns out that the link between religiosity and fertility doesn't go away completely once a society goes through this demographic transition. Religion may be much less important to people's daily lives. And fertility may be much lower—well below replacement levels—but religious people still have more children (p. 16-17). Even when you control for things like wealth and education (p. 119-120).

But that's not all.

It also turns out that religiosity is a heritable trait (p. 49-55). It's only moderately heritable, but the implication is profound nonetheless (it'll just take longer to be realized than if religiosity were strongly heritable). And the implication is this: if religious people have more children, and religiosity is heritable, then, over time, the genes for religiosity should come to dominate the gene pool.

It doesn't matter that an increasing percentage of people in the developed world are unaffiliated with any religion, because they aren't having enough children to replace themselves. Secular genes will live on—since religious and secular people will continue to intermarry and have children together—but they will become increasingly less common as below-replacement fertility continues to siphon them out of the gene pool.

There's something else interesting going on at the same time. The same demographic study which demonstrated that religious women in Europe and North America have more children than their secular counterparts also found something else: the degree of religiosity correlates with the number of offspring a religious woman has (p.16-17). That is, the more religious a woman is, the more children she will have.

Things get especially interesting out at the very end of the religiosity spectrum, among the most intensely religious groups, some of whom have fertility rates greater than 6 children per woman. So far there are only a few religious groups in the developed world with fertility rates this high—the Amish, Mennonites, Hutterites, and Haredi Jews—and they represent a minuscule share of the population, but that can change incredibly fast with a fertility rate more than 3.5x higher than secular people.

For instance, the Amish population in the U.S. and Canada has grown from only about 5,000 individuals in 1920 to over 240,000 in 2010. That's almost 50 times larger in just 90 years. As a point of comparison, in the same time period the U.S. population only grew about 3 times larger and the Canadian population only grew about 4 times larger. Or, to put it another way, the Amish have been growing 12 times faster than the population around them for almost 100 years. And those were 100 years during which the surrounding society saw the advent of automobiles, plane flight, radio, television, computers, the Internet, and mobile phones—essentially everything that makes up modern life.

In Israel, Haredi Jews, who separate themselves from secular society, much like the Amish, are quickly becoming a major portion of the population. As recently as 1990, they comprised only 5% of the Jewish population. Now, they comprise almost 10%. And that number should continue to rise, since they currently make up 29% of the Jewish population under 20 years of age.

So on one hand, we have the below-replacement fertility of secular people siphoning secular genes out of the gene pool. And on the other hand, we have the super-high fertility of ultra-religious sects pumping religious genes into the gene pool. If it continues to be the case that religiosity and fertility are linked—however it is that they are linked—the long term consequences are inescapable: the human race will eventually become more religious (even though it may become less religious for a time while the developing world undergoes demographic transition).

While secular people have been all up in arms about religious fundamentalists not believing in evolution, the religious fundamentalists have been busy, well, winning at evolution.

Further Reading:

1. Religion, fertility and genes: a dual inheritance model, by Robert Rowthorn, is a paper which models what happens to a population's gene pool if there is a high-fertility religious minority (such as the Amish) outbreeding a low-fertility secular majority.

2. The inevitable rise of Amish machines, by Razib Khan, is an article which examines ways in which the fertility differential between religious and secular people may not hold over the long term.

3. Genetic and Environmental Influences on the Traditional Moral Values Triad, by Laura B. Koenig & Thomas J. Bouchard Jr., is a chapter from a larger book on the science of religion that examines the heritability of religiosity (as well as other conservative values).

4. Religion, Religiousness and Fertility in the U.S. and in Europe by Tomas Frejka & Charles Westhoff, is a paper which establishes the fertility differential between religious and secular people in Europe and the United States.

Thanks to Monika Radon-Jones and Guru Khalsa for reading drafts of this essay and providing essential feedback.