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Downloaded by guest on September 24, 2021 a Lehman Clarence planetary the for managing hope consciously signals the of ino pc,rsucs rohrlmtn atr.Vrus (7) Verhulst PNAS factors. limiting other or resources, space, deple- of inevitable an tion face animals—ultimately other and that —, , biological Given ever-expanding all capacities. finite, carrying is ecological to limits is, face growth—that will populations their that presumed have growth growth human difficulties. successive modeling presented but has Anthropocene, the in Populations. basic Modeling the of solutions mirrored popula- of steadfastly human equations. complexity have Between overall the numbers development, equations. of tion technological the all and in amidst social parameters discontinuities, ecological paired pop- the among have human 1 sign equations in (Fig. in those discontinuities growth by ecological ulation modeled growth. sharp processes are population that of precipitated the interactions equations in ecological multispecies to Changes and leading basic cultural changes in by era, evident driven nuclear the were or it agriculture incipient mechanisms. by such to human clues hominins—the —provides of of tree ecology the The on (3). branch discussion cen- the is to therefore responsible tral are mechanisms what Determining R transition demographic prudent guide help can this . to the into us paths delivered trajecto- have have in the that ushered processes Understanding ries three Anthropocene. three all the All and of growthdevelopments instead. cultural population fertility with interlinked uncontrolled controlled been of of regime one a and to them, from upon predators changing as mutualists acting 3) becoming than 2) rather prey, their food than with competitors rather dominant disconti- predators becoming ecological large 1) key of turn: three in occurred past, complexity have prehuman enormous nuities and amidst fit- human that, to reveal our addition they in In well models. data current the to complicated ting correspond more the that of predictions human some provide global and prehistoric Our numbers and known. historic population be pro- of can microscale estimates that parameters match many a of models of provide set minimal effects to a ecology net using cesses, of the model of expert unified by summary a estimated macroscale apply are parame- but we have narratives known Here models precisely opinion. of influential be form cannot most that the the ters of in Some growth, and models. past population and the human explain the of to recognize geolo- seek future to approaches prompting Anthropocene Many planet, term moment. the the present applying on begin force to dominant gists 2020) 29, species a November our review that become for extent (received an has such 2021 to 8, grown April have approved populations and Human CA, Stanford, University, Stanford Daily, C. Gretchen by Edited and 56267; MN Morris, Minnesota, 55108; MN Paul, Saint olg fBooia cecs nvriyo inst,SitPu,M 55108; MN Paul, Saint Minnesota, of University Sciences, Biological of College olwn atu 6,atmt opeithmnpopulation human predict to attempts (6), Malthus Following marked is Anthropocene the of beginning official the Whether cnweg rfudhmnsgaueo h planet. to the 2) on (1, signature Anthropocene human the profound called a been acknowledge have times ecent 01Vl 1 o 8e2024150118 28 No. 118 Vol. 2021 | a,b,c,1 c nttt nteEvrnet nvriyo inst,SitPu,M 55108; MN Paul, Saint Minnesota, of University Environment, the on Institute | oitcadotooitcgrowth orthologistic and logistic ua ouaingot sakyfactor key a is growth population Human hlyLoberg Shelby , | ,wihcrepn ochanges to correspond which A–C), osbls agenda possibilist e eateto nhoooy nvriyo inst,Mnepls N55455 MN Minneapolis, Minnesota, of University Anthropology, of Department d ihe Wilson Michael , | b,c,e n vleGorham Eville and , b doi:10.1073/pnas.2024150118/-/DCSupplemental ulse uy9 2021. 9, July Published at online information supporting contains article This 1 under distributed BY).y is (CC article access open This Submission. y Direct PNAS a is article C.L., This and interest.y paper; competing the no declare wrote authors E.G. paper.The the and edited S.L. jointly analyzed ”orthologistic”; E.G. jointly and term E.G. S.L., M.W., the and S.L., C.L., M.W., coined S.L., ; S.L. C.L., the data; research; designed the the jointly performed jointly E.G. E.G. and and M.W., M.W., S.L., C.L., contributions: Author but populations, projecting for model general a formulate to that ways in data. populations actual human the increased. runaway fit mimic population also the capac- could than carrying That the faster let model increase that a systematically but exhibited ity capacity, disbelief (9) carrying and a Cohen assumed criticism retained that, with long that after met so was dynamics (10). and Twenty-five others the future (11). and the to (8) in opposition Pearl time exact by finite in some was at at This doubling bounds population all kept the that exceed that predict to would equation them found led hyperbolic This and rates. of increasing capacity ever kind carrying a a fitted without of millennia they two assumptions past constraining the the for estimates population human largely have they reasonable, wrong. seemed been largely human Thus, on have capacity (9). carrying populations pause succes- predictable a a without imposing populations models predicted prediction global while others successive but and humanity, each then for (8) surpassed available capacities Pearl carrying data form. of the that sion followed though fit (8) always even not Pearl populations pattern, did century, growth human 20th logistic that he a the assumed that In others form equation”. and now-celebrated “logistic a the with named expectation this modeled eateto clg,Eouin n eair nvriyo Minnesota, of University Behavior, and Evolution, Ecology, of Department owo orsodnemyb drse.Eal [email protected] Email: addressed. be may correspondence whom To u clgcldvlpettu a a epgieu into us guide help can Understanding far future. fertility. thus our of development control ecological related and our successively agriculture, are tools, pre- that to our discontinuities of three ecological those producing great have mechanisms, in evolution ecological and cultural fundamental altered involving societies, changes our ancestors, methods. in human current that complicated more reveal the that They of predictions some provide and with and historic concur unified summarize populations a and apply human understand we prehistoric to multi- Here ecology explain. which of to growth, model sought of our have ecology models understanding ple the requires understanding time Therefore, “the our planet Anthropocene, humans.” the the of as of this time ecology describing are the geologists dominate that so populations Human Significance oegop okn ihdtie essdt ontattempt not do data census detailed with working groups Some fitted (10) al. et Foerster von (8), Pearl after y 30 than More d iiino cec n ahmtc,Uiest of University Mathematics, and of Division b https://doi.org/10.1073/pnas.2024150118 y raieCmosAtiuinLcne4.0 License Attribution Commons Creative . y https://www.pnas.org/lookup/suppl/ | f6 of 1

SUSTAINABILITY ECOLOGY SCIENCE A for populations up to the time of his observations, but was ad hoc in its formulation—simply an ever-accelerating curve that fitted the data. Moreover, that model had no way for the popula- tion to break away from its ever-accelerating path, as eventually it must do on a finite planet. The method explained by Cohen (9) also can fit that range of data, but can break away from its ever-accelerating path only by imposing an external that eventually limits the population. Finally, the use of B expert opinion with ex postfacto analysis does little to explain or predict novel possibilities. Have we overshot our ecological carrying capacity, are we approaching it, or are we well under it as new technological developments might allow? To under- stand the ecology of the Anthropocene, the present analysis applies something different—a single unified model of ecology (4) that accommodates what we and our prehuman ancestors have experienced from our beginning until today (Figs. 1 and C 2), to make sense of our past and to examine our possible future.

Dynamics Shaping the Anthropocene. To expand beyond basic models, human can be cast in relation to such features as land cover and technological advancement (15), but interactions with other species in the food web— through ecological cooperation, , and exploitation— provide an even more complete picture. These interactions Fig. 1. Dynamics of the three major stages in , enabled by cultural change. Representative predator abundance is shown in red, prey can be represented as a three-dimensional unified system of abundance in green, and hominin abundance in blue. All solid curves are ecological equations (equation 1 in Fig. 2), a general form numerical solutions to the ecological equation 1 in Fig. 2, using parame- explored by Volterra (16) and used here to illustrate motifs of ters of SI Appendix, section S1.(A) The hunter-gatherer phase, beginning in basic ecological interactions (4). In certain cases these equa- the remote past when parameter s1,2 in equation 1 in Fig. 2 became neg- tions reduce to one-dimensional form (equations 2 and 3 in ative. Top predators in red were engaged by weapons-wielding hominins Fig. 2). When parameter s is negative, the one-dimensional (left of dashed line), top predators declined to low levels, and hominins form is equivalent to the textbook logistic growth equation, rose to dominate the food web, illustrated here with predator–prey cycling and when s is precisely zero, it represents exponential growth. (right of dashed line). Such cycling is one of multiple possible outcomes from When s is positive, the equation represents orthologistic growth predator–prey interactions, which can also include equilibrium, , and chaotic dynamics. (B) Agricultural phase, beginning when parameter (4), a form that characterizes populations in rapid growth phases. s3,2 became positive, creating a form of mutualism with agricultural animals and crops. The dashed vertical line marks a singularity—a time before which In three-dimensional form, N1 symbolizes the abundance of is guaranteed to be arrested by some ecological, social, top predators, N2 symbolizes hominin abundance, and N3 sym- or physical limitation. Advances in health contribute to the latter parts bolizes prey abundance, which can include animals hunted and of this curve, although the runaway of the curve appears to have plants gathered by hominins. Individual parameters of the form been invariant for millennia. (C) Contemporary phase, when moderation si,j measure how increased abundance of one species affects of human fertility arose in recent centuries as parameter s declined. The 2,2 population growth of the other. For example, parameter s1,2 rep- dashed horizontal lines mark hypothetical carrying capacities—approximate resents the effect that the abundance of species 2 has on the populations where growth rates approach zero, according to equation 1 in s Fig. 2, even with mutualistic interactions intact. The dotted lines represent growth rate of species 1, and 2,2 represents the effect of species possible planned or unplanned reductions in global population to unknown 2 on itself. In general, matched pairs of parameters, si,j and sj ,i , levels, as suggested by Fig. 4, indicating fertilities falling below replacement. categorize the ecological interactions.

Interactions with Predators. The first great ecological discontinu- instead calculate a new population value for each geographic ity in population dynamics involved our early hominin ancestors region by taking the present population of a region, adding and their predators. Rapidly in evolutionary time, as weapons expected births and immigration while subtracting expected and social organizations advanced (17), predators that may have deaths and emigration during an upcoming time interval, in long benefited from hominins as prey instead were harmed by what is described as a “straightforward bookkeeping procedure” their presence. That is, the s1,2, s2,1 pair changed from plus– (12). Projections are developed with expert opinion, which is minus, which is predation, to minus–minus, which represents said to benefit from a lower data requirement than curve fit- competition. With tools and fire, our ancestors outcompeted ting (13), and augmented with “ex postfacto analysis” (13, 14), their predators and eventually dominated the food web (18). But wherein observed errors in previous estimates become adjust- the relationship between our early ancestors and their prey or ment factors to help correct unknown errors in present esti- other food—the s2,3, s3,2 pair of parameters—remained plus– mates. This approach is useful in forecasting populations over minus. A prolonged hunter-gatherer phase persisted over 2 some timescales, but involves increasing uncertainty over long million y. Our early ancestors experienced periodic population timescales. growth and decline (19), complex as in Fig. 1A or more complex All of the methods above are fragmentary in that none can than that. Even during early development of agriculture, long- explain the full range of human population dynamics. Pearl (8) term population growth appears to have been slow, with periods assumed that the world’s population at his time must be decel- of rapid growth punctuated by episodic reductions (20). erating toward a carrying capacity, even though it was increasing at an accelerating rate in terms of percentage of growth, which Interactions with Prey. The second great ecological discontinu- would become evident if his data were plotted in a different form ity began with a seemingly innocuous transformation when our (see Fig. 3B). The method used by von Foerster et al. (10) worked now-human ancestors unconsciously changed the sign of the

2 of 6 | PNAS Lehman et al. https://doi.org/10.1073/pnas.2024150118 Ecology of the Anthropocene signals hope for consciously managing the planetary ecosystem Downloaded by guest on September 24, 2021 Downloaded by guest on September 24, 2021 clg fteAtrpcn inl oefrcncosymngn h lntr ecosystem planetary the managing consciously for hope signals Anthropocene the of Ecology al. et Lehman n nml htw iladeta uulss hyme the interac- meet both they with mutualists, as mutualism eat of mutualism. and requirements kill a plants we domesticated is mathematical consider that agriculture to animals dubious (22), and seem turn noted may in have it Although which feedback others positive species, As a cultivated forming loop. capacity, the carrying of human of increased rights capacity cultivation increased property carrying agriculture and prey, fixed the formerly protection were as that animals intentional and such plants through of fundamental practices resources Then, to involved dispersed (21). economy have the forager from would evolution, a sign cultural in in changes change mere This prey, other and hominins while species. levels, within population and between low at dominate the that rates growth independent 2. Fig. aaee pair parameter hominins where areas become in would levels effect low to overall resided. reduced the were but predators present, as when negligible hominins to risks pose as term such of self-limiting the Summary of (4) sign data. The s discontinuities. population the fit causing to sign in used changes 2, (3) equation dynamics. first- to human a long-term solution Hutchinson for is Explicit suffices of which This expansion (5), (4). growth power-series population equation general for single the of this approximation to order collapse growth their describing terms s for enhancement equations that mutual the shown be to the can according It interacting discontinuity. mutualists second for the after conditions of in appears dynamics 1 Fig. of dynamics the exhibit 1C Fig. to leading +, ( predation (c from and (b) (+, 1A; Fig. mutualism to to leading discontinuity, +, ( first to predation the changed from that causing and ( a) ancestors discontinuities, relationships hominin our the three or cause the us by are control blue under equations in were Coupled that Boxed (1) levels. hominins. trophic by three eaten representing species of abundance the bolizes 2,2 i ,i h pce oetwr xdrto n hntemlil equations multiple the then and ratios fixed toward move species the , sucerdrn h rmrilpae in fprmtr o shown, not parameters of Signs phase. primordial the during unclear is s aaeesaelreyeooia n oil ersniginteractions representing social, and ecological largely are parameters ,cuigtetiddiscontinuity, third the causing (−), logistic to (+) orthologistic from ) s clgcldnmc.Hr the Here dynamics. 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S2 section Appendix, SI r aaeesrpeetdensity- represent parameters ocmeiin(−, competition to −) N 2 and N 3 N when , 3 sym- −), −) indb erpi ihdvlpet fteftr,sc as such future, extinc- the an of such developments Can with 28). repaid (27, be and debt debt species extinction wild tion large displaced our- has a for which food induced growing mutualists, to large our dedicated a and is Still, selves surface carrying limiting. land be the the need of even mutualists portion non- not living partially our where a of synthetic to developing, capacities us with still brought diminished world, these All clothing biological furs. for synthetic and plants cloth and need animals The process. for Haber–Bosch artificial the substituting in crops, created fertilize fertilizer to nitrogen out- animals also for need We the instead. long-established grew fuels for fossil wheels, consuming water also engines and ships substituting and sailing as locomotion such systems and renewable- plows power large to abundant domesti- most other the humans, and (26). Earth with chickens, on dominate now, cattle, are mutualisms corn, species The cated Earth. wheat, the Rice, dominate (25). species human now human the the not just Indeed, represent does mutualism. human 3 multispecies a Fig. Therefore, of in (4). portion as equation dif- curves by single growth represented a be population can in jointly proportions mutualists 2 the ferent equation where of that 2, and form Fig. proportions single-dimensional in fixed the multidimensional approach to 2 the collapses Fig. equation in in 1 equation abundances of form species the orthologistic interactions, in increase overall and the a lags stop serious of not growth. caused did disease, continuation populations, but and local a reversals, of is by collapse disturbances even upturn and Frequent present looking trend. still the longer it much Thus, of growth. not much is with ing 3 stick. it upward, hockey (Fig. rapid that swings a a reveals also flat by portion all—it of flat followed at shape the flat the of of examination as most However, characterized described for explosion, portion commonly recent flat upturn, a long like a seem by may centuries few with detect times. to ancient definitively from difficult available of data be limited could evolution but rate Coupled expected, growth be populations. intrinsic can smaller the in reduced it distress if the even increase tions could agriculture term Early social term. rate each growth affecting intrinsic term lution interaction the social of the in combination maintained and the is mor- by growth and Ecological equations stages. mortality the early local in least increased at by bidity, accompanied been have 3A). postulated (Fig. run- through limits her- broke of repeatedly signature exclude populations as a to growth produced away them pure preda- to mutualisms fenced killed them Keeping and bivores. weeded and competitors, crops, hunted fertilized They eliminate animals, growth. domesticated natural of check with tors that preda- contrast suppress- forces pure, as In mutualisms ing such their depletion. kept (24), ancestors our force mutualisms, they or natural until other disease, only some tion, increase by in mutualisms checked embedded Natural are are webs. remove mutualisms to food all 2, larger Fig. However, ecological in (23). shown than singularity known order the higher from of terms need results pop- tions to it human related of here growth is but rapid This 10), the interactions. singularity. fitting (9, bounds, finite-time in all ulations a earlier so exceed called arose expand soon what is can would populations what they Both in unchecked, 2). that, (Fig. rapidly positive terms tion eetyorseisotrwtene o nmlmutualists animal for need the outgrew species our Recently mutualistic sustained to due increase rapidly species When past the in population human total in increase dramatic The could growth runaway The details. in uncertainties are There equa- the that seem it make may singularity a of presence The s A, n ec ol nuegot nlre popula- larger in growth induce could hence and .Ta stentr frpdyincreas- rapidly of nature the is That Inset). s https://doi.org/10.1073/pnas.2024150118 ihogncadclua evo- cultural and organic with , r PNAS n caused and r | and f6 of 3 r s

SUSTAINABILITY ECOLOGY SCIENCE A thereby increasing population growth, and after a time lag of decades or more, birth rates subsequently dropped, tending to restore a former growth rate (30). Fig. 3B illustrates increasing per capita growth along the red upward-sloping trend line, averaged across the globe. The indi- vidual points and the gray lines connecting them in sequence show deviations from the trend. The global plague marked with the 1350 shows a massive decline in the worldwide rate of growth, indeed to negative values with dimin- ishing. That is also perceptible in Fig. 3A. However, much detail that is obscured in Fig. 3A is revealed clearly in Fig. 3B. Devia- tions below the red trend line are visible when deaths increased, as during the plagues of the past but also during the two 20th- century world , marked with 1915 and 1940. A globally averaged surge above the red 12,000-y trend line appears halfway through the 20th century, as global wars ameliorated (31) and advances spanning , medicine, science, and sanitation B accumulated (32, 33). Mortality markedly fell while birth rates remained relatively unchanged, inflating per capita growth on the global scale, as marked in years 1955 and 1962. This was inter- rupted by tragic regional mortality related to the Great Chinese Famine surrounding 1960. Then, in the mid1960s, the third great ecological discontinu- ity arose, completing the second phase of the modern demo- graphic transition and unexpectedly ending 12 millennia of rapid acceleration. However, unlike standard views of demographic transitions (30), which presume populations will return to their previous rates of growth, birth rates did not fall until they compen- sated for reduced death rates, but began a long-term continuing decline that has now spanned over half a century—marked by the green downward-sloping long-term trend line in Fig. 3B. And that long-term trend suggests viable paths into the future. Demographers have proposed multiple causes of transitions to low fertility (30). Here we emphasize recent changes that reflect the timing of the ecological discontinuity in Fig. 3B, related Fig. 3. World population data. (A) Blue dots show estimated world pop- to the changing status of women in society. This recent effect ulation over time (SI Appendix, section S3). The red curve is equation 3 in corresponds in time to 1) advances in medicine and sanitation Fig. 2 fitted to the data from 10,000 BCE to the 1960s AD, characterized becoming widespread, reducing childhood deaths and making by accelerating growth. The green curve is equation 3 in Fig. 2 fitted to frequent births unnecessary; 2) invention of new synthetic meth- the data since the discontinuity in the mid1960s, characterized by deceler- ods of at the disposition of women, making less ating growth. The × marks the discontinuity. Arrows labeled p and q in the frequent births possible (34); 3) women moving into all aspects main graph are stretched vertically to matching arrows marked p and q in of the workforce (35), making frequent births demanding; and Inset. Points labeled 1 to 8 in the main graph are the same as points 1 to 4) increasing importance of education for gaining employment, 8 in Inset. (B) Per capita growth of the population as a percentage plotted against the population itself. The vertical axis is calculated as 1/N ∆N /∆t , making delayed desirable. Ecologically, the numer- i i i ous factors contributing to the deceleration manifested them- between successive population points, as depicted for ∆N6 and ∆t6 in A, Inset. The light gray lines form a timeline connecting successive data points. selves as a mere change of sign in the self-limiting parameter The upward-sloping red line fits equation 3 in Fig. 2 to the data before s2,2—from positive to negative or becoming more negative (Fig. the discontinuity marked by × in A, representing a 12,000-y-long period of 2, part 4). rapid orthologistic growth. The downward-sloping green line fits the data In the , after only about 50 y of decelerating following the discontinuity marked by the × and projects the data forward growth, the global population continues to increase but births in to a hypothetical equilibrium. The ecological parameter s2,2 shown for both many societies have dropped below replacement levels (Fig. 4), the red-line acceleration phase and the green-line deceleration phase rep- with declines in resident populations compensated in some coun- resents human population growth interacting with mutualistic plants and animals and with continuing cultural development, reaching equilibration tries by immigration. The relative rapidity of this change—just as the percentage growth approaches zero. Note how abruptly the global half a century—may spill over into social disjunction (36). average slope indicated by parameter s2,2 changed from positive to negative Other factors contributed to the deceleration. Increasing at the time of the third discontinuity. attention to consequences of (37, 38) and grow- ing consciousness of Earth’s fragility, visually reinforced by -culture food (29) grown on nutrients extracted from images of the whole Earth from space (39), plus myriad other diverse natural plant materials in restored ? causes (40–44), may also have contributed. Thus, moderation of population growth may have been driven appreciably by local Interactions within. In human populations benefiting from coop- and family-level decisions, where improved and eration and specialization, s2,2 was positive. The more people in decreased childhood mortality enabled families to invest more a society, the more specialists, inventors, and researchers there resources in fewer offspring. could be (9), leading to feedbacks for ever-higher per capita Whether reduced fertility is adaptive—or maladaptive in growth rates. But starting in the 18th century and spreading the sense of decreasing long-term lineage survival—remains in with the , the modern demographic transi- debate (43, 45). What may become important is not genetic fit- tion had its early beginnings. In specific regions, occurring at ness measured by the number of offspring in the next generation, different times in different places, death rates slowly dropped, but rather the number of offspring surviving to create the nth

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Fig. e ihnalo h irpin,w aescesul healed successfully have we disruptions, the of all within Yet the rates, current at continues deceleration the Assuming etlt n dcto.Friiytnst eln ihincreasing with decline to tends Fertility education. and Fertility h utie eeeainpaemeans phase deceleration sustained The b). .With a). sdpbil vial ouainetmtsfo h SCnu Bureau Census US we the in 3), tabulated from Fig. sources, estimates present, other population and to BC available (10,000 publicly dynamics used in population exhibited human cre- is to global used lyze equations parameters the the solve of in to all 1 present We Fig. steps. ate time finite and small over predators, hominins, 1 of (Fig. part dynamics time population over possible prey explore To 1) Methods and Materials the into relatively morphed has our commonplace. repeatedly throughout unimaginable the that history, remember short ecosystem. planetary however, entire should, the We consciously manage the to advance learn and can era an of Anthropozoic? dignity the the into to Anthropocene we ago—to existence will century a our Or suggested elevate “Anthropocene”? (53) Stoppani in geologist “-cene” as able—as timescale, be suffix geological our the the Will on by creatures. blip indicated fellow minor a our and—we be of existence existence that continued modern our expect—for for and planet hope sustainable the can on and a role whole, our create age a to as aware how communica- planet consider become global the to to organize planet. of consciously species to first monitoring paths first first the satellite the prudent the the to and of scope, is us tion awareness global guide Ours conscious our help future. of a to the begun powers into has our planet of magnitude the of tion Forward. Directions have may solutions. problems possibilist intractable seemingly recog- and above, onto described realized including thoughts those world, the such be of superposing problems can physical–biological–social conse- by nized way, unintended desirable this avoid the In to quences. plans that avoided—working laying so undesirable then the events and arrange imag- impossibilities tentatively to and to the tirelessly possibilities working is both Fol- means remains undesirable. ine agenda the What possibilist and the occur universe. desirable lowing the cannot the both impossible—what of including possible, laws is the what by eliminates our and beyond uates not often steps, major few knowledge. a or influence only outcomes events, on human depend In often knowledge. steps or connected influence probability. many our of of beyond domain combinations the from not the derives is that Probability largely events recognizes from human possibilism of problems, attitudes and course local scale, of more global much of range problems also “possibil- self-inflicted the is approaching Pollyannaism, across In to ism.” optimism plane to pessimism separate to cynicism a on ting Agenda. Possibilist The icsin n nihsdrn h eeomn n rsnaino this of for presentation reviewers and the development including Nes- the others during material. Nicholas and insights McGehee, Wendt, and Cordelia Linder discussions Tilman, Marsh, David Kristina bitt, Lehman, Todd Lanyon, ACKNOWLEDGMENTS. 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SUSTAINABILITY ECOLOGY SCIENCE 1. P. J. Crutzen, Geology of mankind. Nature 415, 23 (2002). 29. E. A. Specht, D. R. Welch, E. M. R. Clayton, C. D. Lagally, Opportunities for applying 2. W. F. Ruddiman, E. C. Ellis, J. O. Kaplan, D. Q. Fuller., Defining the we live in. Is biomedical production and methods to the development of the clean a formally designated Anthropocene a good idea? Science 348, 38–39 (2015). meat industry. Biochem. Eng. J. 132, 161–168 (2018). 3. M. Balter, Archaeologists say the ‘Anthropocene’ is here—but it began long ago. 30. J. Johnson-Hanks, Demographic transitions and . Annu. Rev. Anthropol. 37, Science 340, 261–262 (2013). 301–315 (2008). 4. C. Lehman, S. Loberg, A. T. Clark, D. Schmitter, Unifying the basic models of ecology 31. S. Pinker, The Better Angels of Our Nature (Viking, New York, NY, 2011). to be more complete and easier to teach. Bioscience 70, 415–426 (2020). 32. R. A. Meckel, Save the Babies: American Public Health Reform and the Prevention of 5. G. E. Hutchinson, An Introduction to (Yale University Press, New Infant Mortality, 1850-1929 (Johns Hopkins University Press, Baltimore, MD, 1990). Haven, CT, 1978). 33. O. Galor, The and the emergence of sustained economic 6. T. Malthus, An Essay on the Principle of Population (John Murray, London, UK, 1798). growth. J. Eur. Econ. Assoc. 3, 494–504 (2005). 7. P. F. Verhulst, Recherches mathematiques´ sur la loi d’accroissement de la population 34. R. Lee, A. Mason, Fertility, human capital, and economic growth over the [mathematical research into the law of population growth]. Nouveaux Memoires´ de demographic transition. Eur. J. Popul. 25, 159–182 (2010). l’Academie´ Royale des Sciences et Belles-Lettres de Bruxelles 18, 3–38 (1845). 35. W. H. Chafe, The American Woman: Her Changing Social, Economic, and Political 8. R. Pearl, The growth of populations. Q. Rev. Biol. 2, 532–548 (1927). Role, 1920-1970 (Oxford University Press, New York, NY, 1972). 9. J. E. Cohen, Population growth and Earth’s human carrying capacity. Science 269, 36. C. Postelnicescu, Europe’s new identity: The refugee crisis and the rise of nationalism. 341–346 (1995). Eur. J. Psychol. 12, 203–209 (2016). 10. H. Von Foerster, P. M. Mora, L. W. Amiot, Doomsday, Friday, 13 November, A.D. 2026. 37. P. R. Ehrlich, (Ballantine Books, New York, NY, 1968). Science 132, 1291–1295 (1960). 38. S. Greenhalgh, Missile science, population science: The origins of ’s one-child 11. A. J. Coale, H. VonFoerster, P. M. Mora, L. W. Amiot, and growth. policy. China Q. 182, 253–276 (2005). Science 133, 1931–1937 (1961). 39. E. M. Conway, Atmospheric Science at NASA: A History (Johns Hopkins University 12. H. S. Shryock, J. S. Siegel, The Methods and Materials of (Academic Press, Baltimore, MD, 2008). Press, Inc., Harcourt Brace Jovanovich, 1975). 40. P. Ngom, S. Clark, Adult Mortality in the Era of HIV/AIDS: Sub-Saharan Africa (UN 13. J. Bongaarts, R. A. Bulatao, Beyond Six Billion: Forecasting the World’s Population Department of Economic and Social Affairs, Population Division, United Nations (National Academies Press, Washington, DC, 2000). Secretariat, New York, 2003), pp. 1–16. 14. W. Lutz, W. Sanderson, S. Scherbov, The end of world population growth. Nature 412, 41. Q. J. Ding, T. Hesketh, Family size, fertility preferences, and ratio in China in 543–545 (2001). the era of the one child family policy: Results from national and 15. K. Henderson, M. Loreau, An ecological theory of changing human population reproductive health survey. BMJ 333, 371–373 (2006). dynamics. People and Nature 00, 1–13 (2019). 42. D. Bartz, J. A. Greenberg, Sterilization in the United States. Rev. Obstetric. Gynecol. 16. V. Volterra, Variations and fluctuations of the number of individuals in animal species 1, 23 (2008). living together. J. Cons. Int. Explor. Mer. 3, 3–51 (1928). 43. H. Colleran, The cultural evolution of fertility decline. Philos. Trans. R. Soc. B 371, 17. E. P. Willems, C. P. Van Schaik, The social organization of Homo ergaster: Infer- 20150152 (2016). ences from anti-predator responses in extant primates. J. Hum. Evol. 109, 11–21 44. R. K. Jones, J. Jerman, Abortion incidence and service availability in the United States, (2017). 2014. Perspect. Sex. Reprod. Health 49, 17–27 (2017). 18. R. D. Alexander, “Evolution of the human psyche” in The Human Revolu- 45. R. Sear, Evolutionary contributions to the study of human fertility. Population Studies, tion: Behavioral and Biological Perspectives on the Origins of Modern Humans, A Journal of Demography 69, S39–S55 (2015). P. Mellars, C. Stringer, Eds. (Edinburgh University Press, Edinburgh, Scotland, 1989), 46. J. H. Jones, Resource transfers and human life-history evolution. Annu. Rev. pp. 455–513. Anthropol. 44, 513–531 (2015). 19. A. Goldberg, A. M. Mychajliw, E. A. Hadly, Post-invasion demography of prehistoric 47. P. Gerland et al., World population stabilization unlikely this century. Science 346, humans in South America. Nature 532, 232–235 (2016). 234–237 (2014). 20. S. Shennan et al., Regional population collapse followed initial agriculture booms in 48. E. J. Burke, S. E. Chadburn, C. Huntingford, C. D. Jones, CO2 loss by permafrost thaw- mid- Europe. Nat. Commun. 4, 2486 (2013). ing implies additional emissions reductions to limit warming to 1.5 or 2 degrees C. 21. S. Bowles, J.-K. Choi, Coevolution of farming and private property during the early Environ. Res. Lett. 13, 024024 (2018). holocene. Proc. Natl. Acad. Sci. U.S.A. 110, 8830–8835 (2013). 49. G. Ceballos, P. R. Ehrlich, P. H. Raven, Vertebrates on the brink as indicators of bio- 22. M. Pollan, The of Desire (Random House, 2001). logical annihilation and the sixth mass extinction. Proc. Natl. Acad. Sci. U.S.A. 117, 23. W. G. Graves, B. Peckham, J. Pastor, A bifurcation analysis of a differential equations 13596–13602 (2020). model for mutualism. Bull. Math. Biol. 68, 1851–1872 (2006). 50. A. C. Gore et al., Edc-2: The endocrine society’s second scientific statement on 24. J. L. Bronstein, Mutualism (Oxford University Press, 2015). endocrine-disrupting chemicals. Endocr. Rev. 36, E1E150 (2015). 25. V. Smil, Harvesting the : The human impact. Popul. Dev. Rev. 37, 613–636 51. M. Eriksen et al., in the world’s oceans: More than 5 trillion plastic (2011). pieces weighing over 250,000 tons afloat at sea. PloS One 9, e111913 (2014). 26. Y. M. Bar-On, R. Phillips, R. Milo, The distribution on Earth. Proc. Natl. Acad. 52. K. E. Jones et al., Global trends in emerging infectious diseases. Nature 451, 990–994 Sci. U.S.A. 115, 6506–6511 (2018). (2008). 27. D. Tilman, R. M. May, C. L. Lehman, M. Nowak, destruction and the extinction 53. E. Turpin, V. Federighi, “A new element, a new force, a new input: ’s debt. Nature 371, 65–66 (1994). Anthropozoic” in Making the Geologic Now: Responses to Material Conditions of 28. S. Diaz et al., Pervasive human-driven decline of life on Earth points to the need for Contemporary Life, E. Ellsworth, J. Kruse, Eds. (Punctum Books, Brooklyn, NY, 2012), transformative change. Science 366, eaax3100 (2019). pp. 24–41.

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