Demographic Transition Theory, Life-extension Research, And New Questions

Demographic Transition Theory

Population and Life-extension New Questions

Demographic Transition Theory Part One: What is it? Demographic transition theory is a supposition (that sometimes really occurs and sometimes does not) that a population undergoing a population explosion may somehow automatically and gradually correct its excessive growth by slowing down its growth more and more until it returns to stability and equilibrium with its environment. If a graph is drawn of such a population explosion as it gradually slows and returns to stability, the resulting graph is an s-curve (logistic curve) as shown in this article’s cover image. (Notice, however, that this article’s cover also exhibits a second image which importantly shows an s-curve supposition that is crumbling and falling apart.) That is because demographic transition outcomes, despite the hopes, wishes, and suppositions (and/or deliberate deceptions) offered up by some authors, sectors of academe, etc., are not an automatic outcome, are not universal, do not reflect some universal or inviolate rule or law of nature, do not always occur, and do not have to occur at all. So for the sake of humankind, rising generations of under-20s, and the ONLY planetary biospheric life-support machinery so far known to exist anywhere in the universe, let us clarify the picture and broaden our understanding as follows: There are three population patterns that are commonly seen in natural systems. In the easiest of these, a population of organisms may live for decades or even centuries at a time in relative equilibrium with their environment and with other organisms in their surroundings. In such equilibrial conditions, the population’s numbers remain relatively constant, (sometimes with small or recurring seasonal oscillations, etc.) so that a graph of such a population exhibits ongoing stability over time. Occasionally, however, some populations may escape such stability and undergo a sudden POPULATION EXPLOSION in which their numbers begin to skyrocket upward along the y-axis of their population graph. Such population explosions commonly exhibit one of two general outcomes: Sometimes the growth of an exploding population, for varying reasons, begins to gradually slow down more and more, resulting in a gradual return to equilibrial stability as reflected in a classical s-shaped or logistic curve (this first outcome, of course, would be the preferred and hoped-for result envisioned by some who wishfully-contemplate a peaceful demographic transition for humankind). There is, however, a second and exceedingly-dangerous classical outcome of real-world population explosions. And in this second outcome, an exploding population does not slow-down at all, or does not slow-down enough, or does not slow-down in time, and instead continues to rocket upwards in its surroundings until it overshoots the carrying capacity limits of its environment – and results in massive, calamitous, and catastrophic mass die-offs (e.g. 99%-plus die-offs) that result in population-explosion graphs known as “CLIMB-AND-COLLAPSE.” Therefore, what mechanisms and natural principles normally operate to keep populations stable? Populations do not normally explode because whatever their fertility rates are, their numbers are held in check by outside factors such as pathogens or disease, predation, competition with each other or with other species for available food and habitat, and/or by limited supplies of habitat, food, and resources. Thus, population explosions result from a phenomenon known to science as “ECOLOGICAL RELEASE.” Such events occur when one or more of the factors that originally held their numbers in check is suddenly diminished or removed. As a quick example, wild coyotes eat jackrabbits, so when ranchers or dust storms killed large numbers of coyotes, jackrabbit populations suddenly exploded in numbers. Similarly, sea otters along the California coast commonly feed on sea urchins, so when hunters began killing large numbers of sea otters for their pelts, sea urchin numbers suddenly exploded

and their grazing began to threaten the region’s offshore kelp beds. Thus, sudden escape from disease, competition, or predation can serve as an “ECOLOGICAL RELEASE” that results in a sudden population explosion. Possible implications for us? Among the foremost factors that have triggered humankind’s dangerous J-curve population explosion (ecological release) have been our advances in medicine – which have suppressed the pathogens and disease that once held our numbers in check. So we are all grateful, of course, because scientific research and medical advances save lives. A population aspect develops, however, if such medical advances reduce average death rates while worldwide average fertility rates do not diminish accordingly. In another respect, humankind’s population explosion also exhibits an unprecedented sequence never before seen in the history of life on Earth, for we have undergone not just ONE ecological release, but a pattern of one ecological release followed by another and another repeatedly (e.g., multiple ecological releases in medicine, for example, such as antibiotics and transplants, etc., together with other multiple ecological releases in agriculture). And shortly we will address recent research that has already achieved six-fold life-extensions in laboratory organisms. In natural systems, one ecological release and its subsequent population explosion is dangerous enough to invite 99%plus die-offs and/or climb-and-collapse outcomes. But multiple ecological releases, one after another and another and another and followed over and over again on a global and worldwide scale is unheard of – until now

Multiple Ecological Releases: One after Another? Below is a graph of human births and deaths on the island of Sri Lanka in the mid-twentieth century.

Births/1000

Deaths/1000

Sri Lanka: Falling birth rates and falling death rates Upper line: Births/1000 Lower line: Deaths/1000

What on Earth does the above graph of the births and deaths on the island of Sri Lanka in the mid-twentieth century have to do with demographic transition theory and the future of our planet? As the section below will demonstrate, many of today's population projections may be .underestimating. the worldwide population numbers that may emerge in this century. (And where research into life-extension may be about to send us….)

If explosive population growth, for example, poses potentially-dangerous biospheric, humanitarian, and civilizational challenges, then falling birth rates might seem to indicate some easing of the crisis. During the past three decades, for instance,

birth rates have fallen in many parts of the world, so that, if taken on its own, such data might initially be interpreted as a critically-important step in the right direction – (and, in an environmental sense, as potentially good news for our planet).

Births/1000

Deaths/1000

Sri Lanka: Falling birth rates and falling death rates Upper line: Births/1000 Lower line: Deaths/1000

There is just one catch, however, to the above interpretation – and it can be seen in the graph above: Quite often when birth rates are falling (top line), death rates are falling even faster (lower line). Clearly, given our impacts upon our planet, falling birth rates can be considered good news. And falling death rates also constitute good news because we are saving more lives and people are living longer. Ironically, however, when taken together, they add up to biospheric bad news.

Sri Lanka In the decades following World War II the nation of Sri Lanka generated a set of data (as depicted in the…….. above graph) that illustrates the interactive role of birth rates and death rates in a human population. Year 1939 1940 1945 1947 1950 1955 1960 1965 1970 1975 1980 1984

Births per 1000 35 34 38 36 39 35 0 32 33 30 28 25 27

0

Deaths per 1000

Extra per 1000

21 20 20 19 11 . 9 08 09 08 06 06 6

.14 . 14 18 17 28 26 24 24 22 22 19 .21.

This chart outlines the Sri Lanka data set for the years 1939-1984 which was used to generate the graph.

Examine the numbers for 1939, and notice that for every thousand residents of Sri Lanka that year, there were 35 births and 21 deaths. Thus, by the end of 1939, every person who had died had been physically replaced, and then fourteen additional babies were born per 1000.

Next, examine the numbers for 1984. Notice that birth rates fell substantially from 35/1000 in 1939 to just 27/1000 forty-five years later. Initially, this seems like a step toward reducing Sri Lanka's rapid rate of population growth, for with a fairly substantial decline in its birth rate, we might expect Sri Lanka’s population to grow less rapidly. Notice that in the previous page chart, however, that in 1939 there were 14 extra babies per thousand residents, while in 1984 there were now 21 extra babies born per thousand residents. How could this be? What had happened? Even WITH generally FALLING birth rates (35/1000 down to 27/1000 is about 25% reduction) Sri Lanka’s population after more than four decades of falling birth rates found its RATE of population growth had INCREASED by fifty percent. (It was NOW growing larger by 21 extra per thousand instead of the earlier 14 extra per thousand.)

Births/1000

Deaths/1000

In the graph, the top line depicts birth rates over the study period. The bottom line tracks death rates recorded during the same years. If we consider the gap that separates the two lines, we note that in 1939 the gap between births and deaths is fairly narrow. But when we check for its value forty-five years later (1984), the gap had appreciably widened. What had happened? Even though there was a 25% reduction in birth rates, death rates had fallen EVEN MORE (50%). In other words, improvements in health and medicine had completely cancelled out the effects of forty years of fertility reduction …and after 45 years, Sri Lanka’s rate of population growth was EVEN FASTER than it was at the outset. What we see in Sri Lanka's data above mirrors events around the world over the past two centuries (and may foreshadow worldwide events in the decades just ahead). For example, in the 100 years between 1850 and 1950 the world’s most developed countries doubled their populations, "largely due to a decline in the death rate" (Mader, 1996).

Poverty traps We see, therefore, that something very, very important has happened. When today’s less developed countries imported modern medicines following World War II, mortality declines followed quickly, while birth rates remained high and changed little. In contrast to the experience of the developed world, however, today’s Least-Developed Countries do not have the luxury of one hundred years to build infrastructure and adjust to their exploding numbers, because many of today’s poorest and least-developed nations currently exhibit population doubling times as short as 25 to 30 years, and many of them are doubling and doubling repeatedly.

The population of sub-Saharan Africa, for example, has quadrupled since 1950 (e.g., Sachs, 2008). As a result, many such populations are growing so fast that it is impossible for their infrastructure, jobs, educational, and service sectors to keep up. As Mader points out (ibid), “the population of the LDCs began to increase dramatically… and many people in these countries are underfed, ill-housed, unschooled, and living in abject poverty.” Jeffrey Sachs at Columbia University characterizes similar suites of conditions as “poverty traps” (2008). As author Sachs notes, “the decline of fertility lagged behind the decline of mortality, and a massive bulge of population ensued,” and now, “as the world’s population has continued to increase, the threats to human well-being from rising populations have also multiplied” (Sachs, 2008). In effect, humanity today has painted itself into a demographic and environmental corner with few, if any, painless exit options.

Good News and Bad News The good news in Sri Lanka was that: (a) Its birth rates fell, and (b) Its death rates also dropped, saving many lives and allowing its citizens to live longer and healthier lives. Thus, on two fronts, there were significant advances in bettering human lives. Of course, something else was also happening, that, in retrospect, might have been expected: Major advances in medicine, agriculture, and technology lowered Sri Lanka's death rate even more than its birth rate had fallen, partly due to significant progress in the war against malaria. This last fact is the lesson that Sri Lanka holds for the world today: Even if we succeed in lowering birth rates around the world, progress in medical research and biotechnologies may well end up lowering our death rates even more. Thus, while both trends each constitute one sort of good news, at the end of the day, when taken together, our populations could end up growing even faster instead of more slowly. Sri Lanka illustrates the need to look again at our demographic projections for the decades ahead. In those cases where dramatically lower death rates have not been factored in, current projections, which are often presented with an unduly optimistic cast, may turn out to be vastly incorrect. Just as Sri Lanka grew FASTER after three decades of falling birth rates, something similar may be about to happen on a worldwide scale. If a similar set of events takes place worldwide and affects generations now living, world population by 2100 could end up closer to 16 billion than to the 11 billion imagined by recent U.N. projections. And, if we are already close to or beyond Earth's long-term limits, each of these extra and unexpected billions increases the possibility of overshoot and collapse.

Life-extension In this section we will see how medicine, life-extension, and molecular genetics may dramatically affect the demographics of humanity's near future -- beginning with a tiny little roundworm known as Caenorhabditis elegans. Recent studies of C. elegans (and other species) are generating provocative insights into the biology and genetics of longevity and aging (e.g., see Kenyon, 2005; Asencio, et al., 2003, and Friedman and Johnson, 1988). Some experiments, for example, have shown that dietary change in C. elegans can extend lifespan up to 60% (Larsen and Clarke, 2002). Other recent laboratory studies have succeeded in multiplying lifespan six-fold (for example, see Kenyon, 2005).

In a significant review article, Kenyon reports on six-fold extensions of lifespans in Caenorhabditis that have already occurred, noting that in human terms, an equivalent extension would result in healthy, active 500-yearolds (ibid). Although the thought of human approaches certainly comes to mind, pending further research, of course, those possibilities remain, at least for the time being, hypothetical.

It is interesting to envision, however, a human being born in the year 1600 who, at age 33, was alive to witness the trial of Galileo in the Court of the Inquisition. If what has already been accomplished in Caenorhabditis had occurred back then in humans, a person alive to witness such events in 1633 could still be alive today - and with many, many decades of active and healthy life expectancy still remaining. In addition, if anything like such a degree of life-extension in humans were to actually occur in humans, then our populations might be expected to explode at obliterating rates - (unless of course, humankind were to reduce its worldwide fertility rates to replacement-levels of just four-tenths of a child per woman.... per century). Research like that mentioned by Kenyon in her review paper is also being conducted by major universities and the National Institutes of Health (for instance, papers by Sinclair and Guarente, 2006; Larsen and Clarke, 2002; Jazwinski, 2000; and H.Y. Cohen, 2004). Other research labs are targeting a gene (sir2) and its protein (Sir2) that suggests that, “the higher the level of this protein, the longer the life-span for the organisms under study" (e.g., Guarente, et al., 2006, 2004, 2000). "We believe that these studies could lead to... a drug that... provides the benefits of calorie restriction without the extreme difficulty of the regimen itself" (ibid).

Other Recent Advances with Far-reaching Implications What might be the longevity, demographic, and mortality implications of today’s genomics, genetically-modified organisms (GMOs), and similar medical and molecular advances? Recently, scientists have begun testing sets of DNA-based “BioBricks” that, upon insertion into a living cell, may direct cells to carry out various activeties that are spelled-out by the scientists themselves. Though in its infancy, this capability already exists and is under study at labs like those at Caltech, Lawrence Berkeley National Laboratory, Scripps Research Institute, M.I.T., and Columbia (Gibbs, 2004). What if other technologies also lower mortality rates in ways that are not currently incorporated in most population projections? Researchers, for instance, have already generated genes that alternate between two stable states, producing a modified bacterium that exhibits “a rudimentary digital memory.” As just one example, in early 2003, sixteen top students at M.I.T. were “able in one month to specify four genetic programs to make groups of E. coli cells flash in unison” as a demonstration of the new technology’s potential (ibid). Other insights arise from important research at the synthetic biology department at Lawrence Berkeley National Laboratory where Jay Keasling and his team have engineered “a large network of wormwood and yeast genes into E. coli,” enabling the bacterium to synthesize a chemical precursor to artemisinin – an “anti-malarial drug that is currently too expensive for… parts of the developing world that need it most” (ibid). In just three years, Keasling’s lab “increased yields by a factor of one million.” And by amplifying the yields another 25-to-50 times, Keasling anticipates that artemisinin-based medicines might be supplied to the Third World “for about one-tenth the current price.” In a similar way, bioengineered bacteria may be used to produce the cancer drug taxol and other medicines (ibid).

Thus, as our Sri Lanka discussion has shown, falling mortality has repeatedly undermined population projecttions in the past, and current research suggests that the same thing may be about to happen once again – this time on a worldwide basis.

Aeronautics, DNA, and Caenorhabditis Over the past one hundred years, humankind has followed a repeated pattern following new discoveries and technical advances. First there is an initial achievement or discovery that is quickly followed by rapid advances, proliferation, and wide and novel applications. A good example of this is illustrated by the development of aeronauttics: At Kitty Hawk, North Carolina (1903), Orville and Wilbur Wright flew a heavier-than-air vehicle for twelve seconds and a distance of 120 feet. Less than seven decades later, U.S. astronauts traveled to the moon, landed on its surface, and returned safely to Earth again in just over one week.

Similar patterns have also characterized the development of computers, DNA technologies, communications, and molecular biology – each beginning with technical advances, followed by quick proliferation and progression to today's capabilities with breathtaking speed. All of this suggests that today's advances in medicine, molecular genetics, and biotechnologies (including early work like that seen with Caenorhabditis) may have far-reaching impacts on death rates and demographics in the half-century just ahead. Some writers note that genetic engineers will “certainly aim for greater longevity" and, if such engineering proves even "...partly successful, it will create vast social and economic dislocations” (E.O. Wilson, 1998). And, as this article has argued, such advances may well cause humanity to further overshoot calamitous demographic and ecological thresholds.

For now, however, think of the Wright brothers, who in 1903 flew, for the first time, a heavier-than-air vehicle for twelve seconds and 120 feet. Consider next that just sixty-six years later the astronauts of Apollo 11 traveled to the moon and back in a little over one week. Which brings us back to 1993 and the initial doubling of lifespan in individual members of C. elegans. If we envision, beginning in 1993, a life-extension progression similar to that seen in aeronautics then extending 1993 sixty-six years into the future would bring us to 2059. Even if a real possibility of a six-fold / 500 year life-extension for humans were to (or might actually) exist, the exact details and the exact amount of lengthening are of less importance than the fact that: (1) such research is occurring, and (2) that some portion of dramatic success may not just be possible, but may well be probable. Thus, if even a fraction of that 500-year human equivalent were to emerge in the decades ahead (imagine, perhaps, a twenty or a thirty year extension), then today's optimistic U.N. population projections that envision a stabilization of world population or that envision a total medium-fertility world population of 11 or 12 billion around 2100 would go right out the window.

Historically, demographic projections often adopt an assumption of business as usual when modeling alternative demographic futures. Today, such sweeping assumptions are no longer justified. Over and over again, we underestimate the impacts of dramatic and unexpected medical and technical advances and rapid implementation that characterize modern science, research, and genomics. The benefits of each such advance tend to be realized relatively quickly by immediately saving lives and reducing mortality (imagine anti-malarial applications, for example).

At the same time, however, lengthy delays or lag-times occur when traditions, social customs, and fertility adjustments do not occur for decades, if at all. If our early steps in understanding longevity, lifespan, and aging develop and proliferate in a way analogous to the advances we have already seen in biotechnology, aeronautics, DNA, computers, and communications, then precipitous declines in mortality could be on the horizon. If so, then today's demographic projecttions may constitute serious underestimates of Earth's future populations and may lull us into an exceedingly dangerous state of complacency and inaction. Past projections have generated underestimates that have occurred again and again exactly as seen in our data from Sri Lanka. We should appreciate, therefore, that dramatic or unexpected declines in mortality are capable of offsetting or cancelling-out anticipated gains that we otherwise expect based on declining fertility.

Problematic Aspects of Transition Theory Suppose that unexpected medical advances bring about a sudden reduction in mortality. In this circumstance, demographic theory envisions a period of “demographic transition” during which there is a time-delay before reductions in fertility occur to reflect the reduced mortality – and during this lag-time, populations skyrocket as births greatly exceed the lowered death rates. Finally, however (perhaps after one or more generations), transition theory postulates (imagines, hopes-for, wishes-for) a gradual (and sufficient) decline in fertility rates that slowly reduces them to levels commensurate with mortality rates, and a population stabilizes. Thus, too-many demographers commonly envision our time of soaring populations as a transition period during which fertility rates have not yet caught up to our falling mortality rates. And they hope, imagine, and suppose that the transition will complete itself any decade now. One worrisome problem is, however, that such hopes and expectations may well be subverted by a nuanced and unexpected limitation within the theory. How? Why? Because science, medicine, and technology repeatedly lower mortality rates not just once, but over and over and over again – so that we live in a perpetual state of transition. In other words, we repeatedly extend and postpone the period of transition (with its skyrocketing populations) so that its completion never occurs or is repeatedly postponed. In effect, each of our breakthroughs in medicine and longevity re-initiate the transition period, delaying its completion and extending its duration more and more- so that our falling fertility rates are never allowed to catch up.

As fertility rates slowly and gradually adjust to an initial mortality reduction, today’s genetics, technologies, and medical advances institute a second, third, fourth, and fifth mortality reduction in increasingly quick succession. As a result, falling fertility never catches up to the multiple new reductions in mortality and the interim stage of the transition (with its period of soaring population) is never completed. (It may be completed eventually, of course, but with each delay in the transition, the completion is increasingly likely to occur as a collapse.)

What current theory does not fully articulate, therefore, is the role of science, technology, and medicine that are currently making reductions in death rates so quickly and so repeatedly that offsetting fertility reductions do not (or cannot) occur in the short times available. In effect, falling fertility is never able to completely catch-up and conclude the transition, because science and medicine keep perpetually extending the transition over and over again. In the meantime, of course, our already exploding populations continue to rocket to heights and totals that invite collapse. And finally, the coup de grace of all this is that the emerging advances in longevity that we have already seen in Caenorhabditis and other research seem set to perhaps amplify and worsen our current overshoot and carry us past

multiple thresholds and tipping points that should not be transgressed. Most strikingly, our ingenious advances in genetics, molecular biology, and medicine are repeatedly and systematically reducing mortality rates (which we should pursue, of course, and for which their discoverers should be greatly honored and rewarded). The hoped-for transition, however, becomes perpetual and never ends because constant advances keep extending it before it can proceed to completion. Each such advance, therefore, acts to cancel out or neutralize a key expectation of the demographic transition theory and repeatedly postpones completion of the expected transition so that it never occurs or it never ends until our degree of overshoot is so great that complete collapse can no longer be avoided.

More problematic than we currently imagine Realistic population projections need to incorporate at least one variant that contemplates the possibility that widespread and nearly-instantaneous mortality declines may cancel out gains otherwise expected from falling fertility. And these models should also incorporate assorted lag-times and delayed feedbacks that arise from decades of cultural fertility traditions and social customs. If advances in medicine, molecular genetics, and longevity (e.g., Kenyon, 2005) develop and proliferate in ways approximating those we have seen in computers, DNA technologies, communications, and the progress of aeronautics from zero to moon landings in a span of less than seven decades, we could be in more severe trouble than we currently imagine. In short, with maturation of advances that are currently underway, we may see falling death rates in the decades ahead that were unimaginable just a few years ago. Continuation of today’s demographic tidal wave increasingly constitutes the greatest single risk that our species has ever undertaken. Excerpted from What Every Citizen Should Know About Our Planet Used with permission

Footnotes:

1.

This graph, which is known as an S-curve, depicts stabilizing outcomes imagined by Demographic Transition Theory – but such outcomes are not automatic and do not constitute some inviolate law of nature. As one example, ecological release in a population can occur, resulting in a population explosion, overshoot, and climb-and-collapse outcomes that result in massive die-offs, and/or 99% and/or even-worse mass mortalities. Examples: (a) Population explosions of jackrabbits when too many coyotes are killed; (b) Population explosions of sea urchins when too many sea otters are removed (and then the offshore kelp beds begin to collapse in the face exploding pressures of feeding urchins); (c) Similarly, advances in health, medicine, and antibiotics removed diseases that once held humankind’s populations in check (and that was good, of course), but traditional fertility rates did not adjust, birth rates remained unchanged or high, and humankind’s worldwide population explosion today has unfolded as a classical example of ecological release.

Note: In recent years, formal demographic presentations and journal articles often include graphs that depict worldwide population growth as an s-curve. We note here that authors of such s-curve graphs typically do not begin their graphs until the 1960s or so, then (having omitted data from 8000 BC to the present), they bring their graphs up to the present, and project several decades into the future based upon their own hopes, wishes, guesstimates, and suppositions. Readers should consider, however, that in SCIENCE it is not generally permissible to OMIT 9,900 years of population data in order to force-fit one’s graph into a more wishful theoretical configuration. (When, however, all 10,000 years of world population numbers are included in such a graph, the resulting graph is an extreme J-curve as shown in footnote 3 below.)

2. Note that sigmoid curves are not universal in realworld conditions. Instead, multiple real-world populations like this study of a reindeer population in Alaska (after Scheffer, 1951) continue their exponential trajectories and OVERSHOOT the Carrying Capacity of their envir-onment, resulting in another classical population outcome known as “Climb-and-collapse.” In the Scheffer study summarized in this graph, more than 99% of the herd died in the herd’s collapse. In addition, the peak reindeer population in the collapse depicted above occurred when the combined bodies of ALL the reindeer on the island physically-occupied less than 2/1000ths of 1% of the island on which they lived. – in other words, in surroundings that visually appeared to be ALMOST COMPLETELY EMPTY.

3. Lastly, note that the J-curve exhibited by our own graph (shown left) is far more pronounced and far more extreme than the J-curve that preceded reindeer herd collapse and die-off depicted above. Previously, the two most famous J-curves in all of human history were the two atomic detonations that destroyed Hiroshima and Nagasaki at the close of World War II. Now, humankind, civilization, and Earth’s razor-thin surface films of atmosphere, oceans, and seas are living in an obliterating and global-scale J-curve that is unfolding in the middle of the only planetary life-support machinery so far known to exist anywhere in the universe.

References, etc. Bongaarts, 1994. Campbell, Reece, and Mitchell, 1999. Chapin, et al., 1997. Cohen, 2002, 1995. Farrell, et al., 1994. Gallagher, et al., 1995. Hudson, 1989. Myer, 1995. Revelle, 1976, 1974. UNDESA, 2004. Vitousek, et al., 1997. Waggoner, 1994. Wilson, 20