by Larry D. Barnett
The presence of too many people on planet Earth is a problem that generally receives just lip service. The lack of interest in the problem should not, however, be surprising. Hominids have been on Earth for millions of years, and modern Homo sapiens has been around for millennia – by one estimate, for around 141,000 years. Overpopulation as a global problem is an exceedingly recent development, therefore, and given social inertia, human societies today do not acknowledge the role of population size in harmful phenomena that can be manifestations of overpopulation, e.g., crime and inter-group conflict, epidemics of high-fatality disease, elevated levels of migration, and long-lasting food insecurity. Similarly, even though ecosystem degradation is probably the most serious current manifestation of human overpopulation, individuals who are personally concerned with the environment may not be concerned about population growth. Certainly, the two concerns are not strongly related among residents of the United States, despite the disproportionately large ecological impact of Americans.
What should we consider in responding to the problem of overpopulation? My suggestions follow. They arise from my work in social science and in law.
Ecology and Sociology
The biology-based discipline of ecology concentrates on the connections that exist among living organisms and between these organisms and their physical surroundings. Being a branch of biological science, ecology is rarely interested in human societies. In ecology textbooks, for example, human demography may be the subject of a short section, but the study of human societies – how they are structured and how they work – is assumed to be the responsibility of social science, particularly the discipline of sociology. Simply put, ecologists and sociologists have followed very different paths, with each group failing to comprehend key ideas of the other. Even the field known as human ecology, which has had footholds in ecology and sociology and possesses the ability to bring these disciplines together, has been unable to meld the two disciplines since its founding in the first half of the twentieth century.
Of course, the placement of ecology and sociology in distinct realms of scientific endeavor is largely arbitrary. The phenomena that a scientific discipline investigates are not prepackaged and neatly presorted. Rather, the disciplines of science and their boundaries are human constructs; the phenomena on which each discipline focuses have been assigned by scientists. Unfortunately, however, the allocation of ecology and sociology to different, indeed distant, spheres is not just unnecessary. In terms of population–biosphere connections, the allocation is restraining scientific progress because it dissuades ecologists and sociologists from collaborating with one another in efforts to understand the effects of human societies on Earth’s ecosystem and the effects of the planet’s ecosystem on human societies.
A reconciliation of ecology and sociology as scientific disciplines is needed, in short, and the reconciliation may be aided by the concept of “social-ecological system.” In terms of human overpopulation, this concept underscores a pair of principles: (1) since the members of Homo sapiens engage with their environment, the number of human beings drives the scale of human activities; and (2) the scale of human activities drives the state of the natural world. The conclusion – that growth in the number of people increases the scale of human activities and decreases ecosystem health – is backed by a wealth of credible evidence. Moreover, the number of people may damage ecosystems by acting in concert with other environmental factors and hence by creating synergies. If and where synergies happen, the effects that societies of Homo sapiens have on the biosphere can be multiplicative, not merely additive.
The Concept of System
The wall that has been erected between ecology and sociology is not indestructible; it can be at least partly levelled. A first step toward ecology-sociology cooperation may be to recognize that the two disciplines share a concept that is important to both, namely, the concept of system. As a prominent American educator once observed, “an intellectual community” requires “a common language, a common stock of ideas,” but its development is inhibited by specialization. Since the language of science involves concepts, ecologists and sociologists have a basis for understanding one another because they share the concept of a system.
Simply defined, a system is a phenomenon whose parts are interrelated and influence one another. Given these attributes, a system is a whole that is more than the sum of its parts. The idea of a system is inherent in ecology because ecology often focuses on ecosystems. The idea of a system is inherent in sociology, too, because sociology (or at least macrosociology) focuses on human societies, and each society is a system rather than an assemblage of unconnected individuals. If increases in the population of Homo sapiens that are being produced by human societies are to be brought to an end by non-Malthusian means, we must not overlook the system character of society as well as the system character of the biosphere.
Let me turn now to the question of why the system aspect of human society is critical when seeking interventions that will halt or reduce growth in the number of people. The answer is that a society, being a system, has a tendency toward social integration as well as system integration, and it therefore resists alterations to its present course. The resistance is manifested in actions by a society that neutralize interventions and/or by actions that redirect interventions away from their intended targets. As a system, a human society may thus behave in unanticipated, even counterproductive, ways when subject to an intervention such as the adoption or removal of a particular proscription or prescription of law. Unfortunately, sociology knows very little at the moment about the social side effects of law, but these effects may be frequent and significant. Consequently, solutions to overpopulation must be accompanied by the conscious realization that every proposed solution carries the risk that it will not work at all, or may even work to worsen matters. Simply said, the law of unintended consequences is an ever-present possibility and may lay waste to an otherwise attractive solution.
Social Side Effects of Law
To illustrate social side effects that have resulted from the introduction of new law, I offer two case studies. Because the case studies involve law topics that are different in objective and come from societies that are sociologically dissimilar, they suggest that law-generated social side effects are not uncommon. Ecologically, as biologist Garrett Hardin observed, “we can never do merely one thing.” Sociologically, the same principle applies.
The first case study is the policy adopted by China in 1979 that was designed to curtail domestic population growth by imposing a one-birth maximum on each Chinese woman who belonged to the majority (Han) ethnic group. The policy, which lasted more than thirty years and may have been “the largest social experiment in human history,” surprisingly made an uncertain contribution to lowering the level of childbearing in China. However, while the policy may not have dampened childbearing, it did have social side effects – the policy substantially raised the sex ratio (the number of males per 100 females) and materially increased the crime rate. In addition, the policy affected Chinese society by (1) altering the marriage rate and the choice of marriage partners, (2) increasing the incidence of crimes committed by females, and (3) causing the abandonment, surrender, and abduction of children. The policy, in short, did not escape the law of unintended consequences.
The second case study comes from the United States and involves the federal Voting Rights Act of 1965. The aim of the Act was to prevent government from discriminating on the basis of race in determining which U.S. citizens are qualified to cast a ballot in elections. As an illustration of the social side effects of law, the Act is important because it has been ranked at the pinnacle of U.S. civil rights statutes and acclaimed for its role in combatting discrimination in suffrage against racial and ethnic groups in jurisdictions where such discrimination was at its worst. But although the Act has been described as “a momentous achievement,” did it have a major, long-term impact on race-based disparities in American political affairs? Given the widespread assumption that law alters social patterns and ameliorates social problems, a positive answer to the question would be anticipated. However, as I explain in detail elsewhere, credible evidence exists to conclude that the Act, through the social stress that it produced, was probably responsible for a reduction in the ability of the black population living in southern U.S. states (the main target of the Act) to sway election outcomes. The likely reduction occurred because, in response to the Act, many more whites than blacks registered to vote.
These two case studies supply a lesson in macrosociology to advocates of law and government policy, including those who want to end the numerical growth of species Homo sapiens. Briefly stated, human societies can generate outcomes that are at variance with what advocates of particular law and policy measures hope to accomplish. Such unanticipated outcomes happen because a society is a complex system. Regrettably, sociologists today are largely in the dark regarding social side effects that sabotage law and policy. As a result, proponents of measures to dampen population growth should remember the adage to “look before you leap.”
How can sociological traps that produce severe, counterproductive side effects be avoided? One possible way to sidestep the traps may be to formulate law and policy measures in a setting that is multidisciplinary and interdisciplinary. The intellectual tent under which measures concerned with population growth and size are constructed will have to be very broad, because the measures must build on expertise from an array of disciplines. Among these disciplines are (in alphabetical order) demography, ecology, economics, ethics, political science, psychology, religion, and sociology. The effort will necessarily involve numerous disciplines because the overpopulation of Homo sapiens is not a simple, unitary problem. Its solution will unavoidably possess an antinatalist goal, and it will also need to address migration within and between countries because of geographic differences in the intensity of population pressures on the biosphere.
Moreover, a persuasive case can be made that globally the size of the human population is already too large and should be reduced: Since the early 1970s, as seen in the graph below, levels and types of resource consumption and disposal are estimated to have required more than one Earth to sustain indefinitely the then-current population of the world with then-existing technologies and modes of resource management. This “ecological footprint,” which encompasses “all the mutually exclusive, biologically productive spaces that human activity demands,” is an indication that Earth’s ecosystem is unable over the long run to maintain Homo sapiens globally in its present country-specific lifestyles and at its present numerical size. Yet at least in democracies, attempts to alter levels of childbearing and migration have not been particularly successful to date, according to available social science research. Future attempts may have a higher probability of success if they are based on a wide range of expertise.
Larry Barnett is Professor Emeritus, Widener University Delaware Law School, Wilmington, Delaware USA. His recent publications include the two-volume work Societal Agents in Law (Palgrave Macmillan, 2019) and Demography and the Anthropocene (Springer, 2021). He is currently finalizing a book-length manuscript titled Societal Stress and Law.
 Fiorenzo Facchini, Man, Origin and Nature, in Interdisciplinary Encyclopedia of Religion and Science (G. Tanzella-Nitti et al. eds., 2002), http://inters.org/origin-nature-of-man (last visited May 2, 2021).
 Nelson J. R. Fagundes et al., Statistical Evaluation of Alternative Models of Human Evolution, 104 Proc. Nat’l Acad. Sci. 17614, 17615 tbl. 1 (2007).
 The evidence that these and other problems are generated by overpopulation is cited in Larry D. Barnett, Demography and the Anthropocene 19–31 (2021) [hereinafter Demography and the Anthropocene]. In addition, see Monica H. Green, The Four Black Deaths, 125 Am. Hist. Rev. 1601 (2020) for a recently published historiographic study of the Black Death pandemic and its impact on human societies. The Black Death, which was caused by a bacterium, may be the single worst pandemic ever experienced by Homo sapiens and was magnified by areas of human-population concentration. Green, supra, at 1601, 1603, 1607, 1627. Professor Green advances the thesis that the Black Death pandemic “was even larger than previously imagined,” having begun a century earlier and been far more geographically widespread than commonly assumed. Green, supra, at 1602, 1607, 1615, 1625, 1627.
 For the design and findings of the study on which this conclusion is based, see Demography and the Anthropocene, supra note 3, at 35–50.
 Id. at 10, 11–13 & fig. 1.3.
 Ecology has been defined as “that branch of biology which deals with the relations of living organisms to their surroundings, their habits and modes of life, etc.” Oxford English Dictionary (def. #1 of “ecology”) (2nd ed. 1989; CD-ROM ed. 2009).
 Peter J. Richerson, Ecology and Human Ecology: A Comparison of Theories in the Biological and Social Sciences, 4 Am. Ethnologist 1, 2 (1977).
 William R. Burnside et al., Human Macroecology: Linking Pattern and Process in Big-Picture Human Ecology, 87 Biological Rev. 194 (2012). Professor Burnside and his coauthors propose a field of study that they name “human macroecology” and believe that it can bridge the current divide between the natural sciences and social sciences. The field of human macroecology, as they define it, would focus on interactions between humans and their environment “across spatial and temporal scales, linking small-scale interactions with large-scale, emergent patterns and their underlying processes.” Id. at 206.
 Paul Shepard, Whatever Happened to Human Ecology?, 17 BioScience 891 (1967).
Within sociology, the subdiscipline of environmental sociology emerged during the early 1970s. Jean-Guy Vaillancourt, Sociology of the Environment: From Human Ecology to Ecosociology, in Environmental Sociology: Theory and Practice 3, 5 (Michael D. Mehta & Eric Quellet eds., 1995). However, environmental sociology largely accepted established sociological thinking rather than develop novel ideas, and attracted few sociologists. Donna E. Hughes, Environmental Sociology: A Distinct Field of Inquiry?, in Environmental Sociology: Theory and Practice, supra at 61, 76-77.
 See Richerson, supra note 7, at 1 (citing a book published in 1938 and authored by an ecologist; describing the ecologist as being “interested in human ecology”); Amos Hawley, Ecology and Human Ecology, 22 Soc. Forces 398 (1944) (contending that human ecology arose as a field of specialization in sociology “in the early 1920s”).
 Marion Glaser et al., New Approaches to the Analysis of Human–Nature Relations, in Human–Nature Interactions in the Anthropocene: Potentials of Social-Ecological Analysis 3, 4 (Marion Glaser et al. eds., 2012) (proposing the concept of “social-ecological system” and defining such a system as “a complex, adaptive system consisting of a bio-geophysical unit and its associated social actors and institutions”).
 Demography and the Anthropocene, supra note 3, at 19–31.
 Id. at 23, 30–31.
 Sophie Peter, Integrating Key Insights of Sociological Risk Theory into the Ecosystem Services Framework, 12(16) Sustainability art. 6437, at 1, 12–15 (2020).
 Alexander Backlund, The Definition of System, 29 Kybernetes 444 (2000).
 John Urry, Sociology and Climate Change, 57(supp. 2) Sociol. Rev. 84, 84–85 (2009).
 David Lockwood, Social Integration and System Integration, in Explorations in Social Change 244 (George K. Zollschan & Walter Hirsch eds., 1964). The posited predisposition of a human society toward social integration and system integration is a proposition of structural-functionalism theory. Id. Structural-functionalism theory as it applies to marriage and childbearing is discussed in Demography and the Anthropocene, supra note 3, at 53–57.
 Larry D. Barnett, Societal Stress and Law ch. 1 (unpublished manuscript, 2021).
 Quoted in Carl Jay Bajema, Garrett James Hardin: Ecologist, Ethicist and Environmentalist, 12 Population & Env’t 193, 204 (1991). See also Garrett Hardin, An Ecolate View of the Human Predicament, 7 Alternatives 242, 246 (1981) (proposing education in “ecolacy” to foster the realization that, because human beings live in an environment of interconnected parts, human interventions in the environment usually do not have a high probability of yielding the outcomes desired).
 Wei Huang, How Does the One Child Policy Impact Social and Economic Outcomes?, IZA World of Labor, Sept. 2017, at 1, 2–3.
 Francisco Zamora López & Cristina Rodríguez Veiga, From One Child to Two: Demographic Policies in China and their Impact on Population, 172 Revista Española de Investigaciones Sociológicas 141, 142, 154 (2020).
 Huang, supra note 21, at 9.
 López & Veiga, supra note 22, at 144–46.
 Hongbin Li et al., Estimating the Effect of the One-Child Policy on the Sex Ratio Imbalance in China: Identification Based on the Difference-in-Differences, 48 Demography 1535, 1554–55 (2011). See generally Emily A. Stone, Does Mate Scarcity Affect Marital Choice and Family Formation? The Evidence for New and Classic Formulations of Sex Ratio Theory, 55 Marriage & Fam. Rev. 403, 417–18 (2019) (concluding from a review of research that, ceteris paribus, a high ratio of men to women raises the rate of marriage and also increases the marriage of women to men who are higher in socio-economic status).
 Lena Edlund et al., Sex Ratios and Crime: Evidence from China, 95 Rev. Econ. & Stat. 1520, 1533 (2013) (using data combining violent and property crime). The higher crime rate may not have been due to the larger number of males. Indeed, an increase in the sex ratio may lower the rate of violent crime. Ryan Schacht et al., Marriage Markets and Male Mating Effort: Violence and Crime Are Elevated Where Men are Rare, 27 Hum. Nature 489, 490, 497 (2016) (using data on the United States).
 Wei Huang & Yi Zhou, One-Child Policy, Marriage Distortion, and Welfare Loss 4–5, 16 & n.22, 18–19, 21, 26–28 (Inst. for the Study of Labor (IZA), Discussion Paper No. 9532, 2015).
 Tina Wang, Fewer Women Doing More Crime: How Has the One-Child Policy Affected Female Crime in China?, 61 Sociol. Q. 87, 94, 98–99, 101 (2020).
 Xiaojia Bao et al., Where Have All The Children Gone? An Empirical Study of Child Abandonment and Abduction in China 13–14, 24, 26–27, 31–32, 35 (Nat’l Bureau of Econ. Res., Working Paper No. 26492, 2020).
 Instances of human-rights abuses in China under the one-birth policy have been documented. Ying Chen, China’s One-Child Policy and Its Violations of Women’s and Children’s Rights N.Y. Int’l L. Rev. 1, 57–65 (2009). Such abuses, by increasing social alienation, would have reduced social integration in Chinese society. See supra note 18 and its accompanying text. See also Blogs of The Overpopulation Project on the topic of human-rights abuses pertaining to reproduction; the blogs are at https://overpopulation-project.com/?s=coercion.
 Pub. L. No. 89-110, 79 Stat. 437 (1965) (codified as amended at 52 U.S.C. § 10301 et seq. (2021)). The current version of the United States Code, including title 52, is accessible at https://uscode.house.gov/download/download.shtml.
 “No voting qualification or prerequisite to voting, or standard, practice, or procedure shall be imposed or applied by any State or political subdivision to deny or abridge the right of any citizen of the United States to vote on account of race or color.” Id. at § 2 (codified as amended at 52 U.S.C. § 10301(a)).
 Justin Levitt, Section 5 as Simulacrum, 123 Yale L.J. Online 151, 151 (2013).
 Nat’l Archives Found., Voting Rights Act of 1965, https://www.archivesfoundation.org/documents/voting-rights-act-1965.
 Societal Stress and Law, supra note 19, at ch. 1 pt. 1.6 & app. B. My analysis in the foregoing source is based on the findings of Adriane Fresh, The Effect of the Voting Rights Act on Enfranchisement: Evidence from North Carolina, 80 J. Pol. 713 (2018).
 The Oxford English Dictionary does not define either the word “antinatalist” or the word “antinatalism.” Oxford English Dictionary (2nd ed. 1989; CD-ROM ed. 2009). The concept of antinatalism is variously defined, but generally means “opposition to procreation.” Antinatalism Int’l, What is Antinatalism?, https://antinatalisminternational.com/what-is-antinatalism.
 Demography and the Anthropocene, supra note 3, at 11–13 & fig. 1.3.
 The Global Footprint Network estimates that, since 2010, the human population of the world would have needed approximately 1.7 Earths to have enough “biologically productive land and water . . . to produce all the resources it consumes and to absorb the waste it generates, using prevailing technology and resource management practices.” Global Footprint Network, https://data.footprintnetwork.org/#/abouttheData (definition of “ecological footprint”). The estimates are available for each year from 1961 through 2017. Global Footprint Network, Country Trends, https://data.footprintnetwork.org/# (under “Explore Data”, select “Reserve/Deficit Trends”; on the “Country Trends” page, select “Ecological Footprint (Number of Earths)” and then “Download Data”) (last visited May 23, 2021).
 Global Footprint Network, Ecological Footprint Accounting 10 (2020), https://www.footprintnetwork.org/our-work/ecological-footprint/limitations-and-criticisms. “Mutually exclusive” spaces prevent the same space from being counted more than once. Id. at 10 n.10. See id. for a general discussion of the limitations of the ecological footprint measure.
 Citations to this research are in Demography and the Anthropocene, supra note 3, at 62–64. For example, as to childbearing, a review of multivariate research concluded that the effect on fertility of fertility-supportive government policies “tends to be small” and that the effect of these policies may be on when women bear children (i.e., birth timing), not on how many children they bear. Anne H. Gauthier, The Impact of Family Policies on Fertility in Industrialized Countries: A Review of the Literature, 26 Population Res. & Pol’y Rev. 323, 331, 334, 339 (2007). Accord, Jochen René Thyrian et al., Changing Maternity Leave Policy: Short-term Effects on Fertility Rates and Demographic Variables in Germany, 71 Soc. Sci. & Med. 672, 673, 674 (2010) (studying a region of Germany; using data on births in the region over twenty-three months after the adoption of new government regulations promoting maternity leave and financial support for childbearing; finding that the regulations, which took effect in January 2007, had no impact on the rate of childbearing). In addition, see Larry D. Barnett, The Place of Law: The Role and Limits of Law in Society 440–41 n.67 (2011) (citing, and summarizing the findings of, social science studies of the impact that changes in law specifying the permissible grounds for abortion had on the incidence of abortion; concluding from these studies that law on abortion has not had a substantial effect on the frequency of abortion).
As to immigration, see Demography and the Anthropocene, supra note 3, at 63–64 n.52 for studies of the impact of U.S. government policy on the scale of immigration into the United States. Another study, which is not cited in Demography and the Anthropocene, found that city governments in the United States that had adopted policies unfavorable to immigrants did not have smaller foreign-born or Hispanic foreign-born populations than city governments that had adopted policies favorable to immigrants. Daniel Hummel, Immigrant-Friendly and Unfriendly Cities: Impacts on the Presence of a Foreign-Born Population and City Crime, 17 Int’l Migration & Integration 1211, 1218–19, 1224 tbls. 7 & 8, 1226–27 (2016). Anti-immigration policies of cities thus did not reduce, and pro-immigration policies of cities did not increase, the presence of persons who were born outside the United States, including persons of Hispanic ethnicity.
Research on the immigration policies of nations worldwide suggests that (1) the effectiveness of such policies is circumscribed by “powerful structural migration determinants,” i.e., social, economic, and demographic conditions; and (2) because of unintended policy effects, such policies, while decreasing the number of immigrants who arrive in a country, can also decrease the number of immigrants who after arrival leave the country. Immigration policies, accordingly, do not necessarily alter the net rate of migration experienced by a nation or the number of immigrants who reside in the nation. Hein de Haas et al., International Migration: Trends, Determinants, and Policy Effects, 45 Population & Dev. Rev. 885, 887–88, 914 (2019). Thus, a review of research concluded that the immigration policies of nations have had a larger impact on “the [place of] origin and internal composition of migration . . . than [on] the overall volume and long-term trends of migration.” Mathias Czaika & Hein de Haas, The Effectiveness of Immigration Policies: A Conceptual Review of Empirical Evidence 5, 23 (Univ. of Oxford Int’l Migration Inst., Working Paper No. 33, 2011).