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From More Than Human

Ramez Naam examines the future of population in the light of advancing healthy life extension technologies, a discussion reprinted with permission from his book More Than Human.

Copyright © Ramez Naam.

How will longer lives affect world population? Certainly anything that keeps people alive longer will increase the number alive at any given point. However, the details of population growth can be rather counterintuitive. Consider that today the countries with the longest life expectancies at birth have populations that are remaining steady or even shrinking. For example, the UN Population Division expects the populations of Japan, Italy, Germany, and Spain to all decrease over the next 50 years, despite the fact that Japan has the highest life expectancy of any large country, and the Western European nations are not far behind. At the other extreme, the countries with the fastest growing populations are those with relatively low life expectancies - countries like India, China, Pakistan, and Nigeria.

Throughout most of human history, birth rates and death rates were both extremely high. In the year 1000 AD, birth rates were around 70 births per 1000 people per year, and death rates were about 69.5 deaths per 1000 people per year. So each year a town of 1000 people would on average increase its population by half a person. That's a 0.05 percent rate of growth.

As societies advance, nutrition, sanitation, and medicine all serve to lower the death rate. When births outstrip deaths, population soars, as happened through the twentieth century. But in the last few decades the birth rate has also dropped sharply, particularly in the rich developed nations of the world. As countries gain in wealth and education, and especially as women in those countries gain greater rights, resources are increasingly devoted to education and career, rather than raising a family. This demographic trend is spreading from Europe, Japan, and North America to the rest of the world. Worldwide the birth rate is now 21 births per year per 1,000 people. The death rate is around 10 deaths per year per 1,000 people. So overall the world population is growing at roughly 1 percent, slower than at any time in the last few centuries.

Because the birth rate is double the death rate, phenomena that affect fertility can have a far larger impact than similar size effects on the death rate. For example, between 2000 and 2050, the UN expects around 3.7 billion people on earth to die, while another 6.6 billion are born. Cutting the death rate in half would increase population by around 1.9 billion people. Doubling the birth rate would increase population by a further 6.6 billion. Thus the birth rate is a more significant lever on the size of the population.

Projecting population growth into the future is a tricky thing. It depends on just how quickly economic growth improves healthcare, sanitation, and nutrition. It also depends on how quickly those important birth rates come down. The United Nations Population Division produces high, medium, and low estimates for future population. Birth rates and death rates differ by just a few percent between the scenarios, but over decades it adds up. In 2000, world population stood at 6 billion people. Looking forward, the UN predicts that in 2050, world population will be somewhere between 8 billion and 11 billion, with a "medium" prediction of 8.9 billion.

8.9 billion people is half again as many as are alive today. Yet in real terms it represents a growth rate about half as fast as the last 25 years. World population grew by 50 percent between 1975 and 2000. The next 50 percent increase is predicted to take until sometime after 2050, around twice as long. Ultimately the UN's "medium" model projects world population hitting a plateau of 10 billion people in 2100. Of course, projections 100 years in the future are perilous. They rely on a generally smooth progression of current trends. They don't take into account the possibility of global plagues, world wars, or technologies that radically alter mankind.

Life extension is just one of those technologies, yet its impact on population is surprisingly small. Demographer Jay Olshansky, despite being a pessimist about the prospects for slowing human aging, has shown that extending human life would have an incremental, rather than exponential, effect on population. "The bottom line is that if we achieved immortality today, the growth rate of the population would be less than what we observed during the post World War II baby boom", he says. If everyone were made completely immortal today, he calculates, and taking into account declining birth rates, global population would hit about 13 billion in 2100, rather than the 10 billion currently projected.

The immortality Olshansky is talking about isn't achievable. If we halted all aging, accidents, homicide, suicide, and infectious diseases would still kill people. Nor is complete halting of the aging process in our sights today. More likely, we'll achieve the technology to slow but not halt the rate of aging in the next 10 to 20 years. Then it will take additional years for people around the world to gain access to the technology. Even then, the impact on population won't be instant. Those who are already old won't benefit much from techniques that slow their aging rate. Instead, it will be the middle aged and young who reap most of the benefits. The combination of those factors suggests a gradual impact on worldwide population.

Here's a simple mathematical way to look at this. We can't predict exactly when life extension techniques will first be available or how quickly they'll spread, so we'll need to make some guesses. Imagine that life extension techniques first appear on the market in 2015. In the year after that (2016), let's say the overall death rate around the world drops by 1 percent as a result. And let's say that it decreases by another 1 percent each year thereafter, so that in 2017 age-slowing techniques have reduced the global death rate by 3 percent, and that by 2050 they've reduced it by 35 percent. That's quite an optimistic scenario. It implies that by 2050 we've managed to increase life expectancy in the developed world to around 120, and in the developing world to around 113 - an unprecedented rise in life expectancy, even compared to what's happened in the last two centuries.

If this extremely optimistic rise in life expectancy occurred, how large would the impact on global population be? If we simply reduce the number of deaths the UN forecasts each year by the percentages above (1 percent in 2016 climbing up to 35 percent in 2050), we get a total population in 2050 of 9.4 billion people, instead of the 8.9 billion the UN projects.

Five hundred million additional people are nothing to sneeze at, but as a proportion of the projected world population for 2050, it's less than 6 percent. To put this in context, that's less than the percentage change in world population between 1970 and 1973 - a noticeable change, to be sure, but not a catastrophic one.

It's also worth noting that some demographers believe that birth rates in the developing world will drop faster than the UN's middle scenario. Just a 5 percent lower birth rate yields a scenario where global population tops out at around 8 billion in 2050, and may come back down to below the year 2000 level of 6 billion in 2100. Achieving this is entirely plausible if the right resources are applied. A plateau and eventual reduction in global population depends on the spread of wealth, education, and freedom in the developing world. For example, the UN expects the population of Europe (not counting immigration) to shrink by about 0.4 percent per year between now and 2050. The overall population of the developed world (again not counting immigration) is expected to remain fairly constant. If the developing world can attain the present level of affluence of the developed world by 2050, we'll see overall world population level out and begin to drop.

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