**The human population of the earth is now about 7 billion. Scientists who study these things think that the “sustainable” population is between 1.5 and 2.5 billion. Although the rate of increase has lessened in recent years, the population will continue to increase for some time unless mankind takes aggressive action to stabilize it. The Chinese government has attempted to rein in their population by limiting some families to one child. It occurred to me that society would change in some rather unexpected ways if that were implemented worldwide. Limiting birthrate causes a shift in the average age of the population. What would be the result of such a draconian policy if it were left in place for an extended period?**

**Now as a computer programmer, I suppose I could write a simulation program that would show the results over time of such a regimen. But that would be a lot of work, and would involve a lot of estimates and guesses, so I doubt if it would be very accurate.**

**But if I am mainly interested in gaining insight into the general consequences of draconian population control, all that effort is not required. I can build an imaginary “model” that anyone can understand and as you will see, it will demonstrate some unanticipated consequences.**

**So…here we go.**

**Imagine a ladder with exactly 87 steps. Each step represents a year of life. Now in my absurdly simple model, we will start with 64 people on each step…and 64 newly born babies, less than one year old sitting on the ground below the first step…step zero, you could call it. Each year, the babies move up to the first step…and new babies occupy the ground below them. And the one-year-olds move to step 2, etc. When the people on the 87th step try to go up to the next…there isn’t one. Everybody lives exactly 88 years.**

**When the people on the 21st step advance to the 22nd, they pair up (married or not) and have one baby…who immediately crawls down to the ground below the first step.**

**So let’s set this thing in motion. Click…and everybody moves up a step…babies pop out at step 22…exactly one per couple. So if we have 64 people…32 couples…then every year, 32 babies appear and crawl (they can’t walk yet) down to step zero…and 64 people will disappear off the 87th step.**

**After 22 clicks, that first group of 32 babies makes it to step 22. But since there are only 32 of them…16 couples, the new group of babies is only 16.**

**Fast forward another 22 years and the new group numbers only 8.**

**Go forward 21 more years, just before the first group of 8 hits the 22nd step. Now, consider the occupancy on the ladder at this point. The bottom 22 steps (0-21) have 8 young people between 0 and 21 years old. The next 22 steps have 8 young couples between 22 and 43 years old, working and raising their child. The next 22 are middle age folks between 44 and 65, working and doting over their grandchild. The topmost 22 steps have 64 people between 66 and 87 years old enjoying retirement and their status as parents, grandparents and great-grandparents.**

**It’s convenient to think of the ladder in quartiles of 22 years each. The first quartile is childhood and education period. Second and third are family and working life, the last is retirement. We are interested in the proportion of people in each quartile, so we can just think of the number of people on each step: 8, 16, 32, 64. Notice that the steps in the top quartile have more people than the other three combined. More retirees than workers and kids! How does that affect the economy? And pension funding?**

**Those things are obvious. Here are some that are not. The first 22 years, the population goes down 32 people per year. (64 people die, 32 new babies) At the end of 22 years, the population has declined by 704…12.5% from the original 5632. Too slow, you say? Hang on to your hat. The second 22 years, the population goes down 48 people per year, (64 – 16) but the base for calculating the percentage is 4928, so the actual percentage decline over the next 22 years is 21.4%…almost double.**

**The acceleration continues. The next 22 years, the population goes down 56 people per year resulting in a 22 year decline of 30.5%. After that, every 22 years, the population declines by 50% as long as the 1 child per couple regimen is maintained. Furthermore, the percentage of couples in childbearing years declines steadily until it stabilizes after 66 years at about 10% of the population. Clearly, such a regimen could not be maintained for many 22 year cycles without risking extinction if, for instance, an epidemic occurred that killed the small number of females of childbearing age. There is also the threat of a diminishing gene pool, decreasing genetic diversity that makes populations resistant to diseases.**

**Looking back at where we started, with 64 people on each step…5632 total…after 66 years the population is 2640, and it goes down 50% every 22 years after that.**

**As I said, after 66 years, over 50% of the population is 66 or older. Just to put that in perspective, as of 2010, 15% of the US population was 65 or older. Many third-world nations with high birth rates have much smaller over-65 populations.**

**What kind of society would we have if the elderly were in the majority? Probably less warlike and less dynamic and entrepreneurial. Old people buy less, consume less, and are less willing or able to work 16-hour days to realize their dream of a starting a successful business. Economic activity would be lower per-capita. The economy of the US would undergo a radical transformation. Capitalism needs growth, growth, growth and ever increasing profits. Ain’t gonna happen when the population is going down more than 2% per year (after 66 years) and most people are old. I cannot even imagine what the world economy would look like under this scenario. Massive depression, scarcity of jobs? Maybe not, only 40% of the people are working.**

**Of course, this exact scenario would never occur in the real world, but it contains some hints of problems that humankind needs to think about as we head into a future that will inevitably require population and consumption limits.**