Introduction

1I was introduced to Jean-Pierre Bocquet-Appel (JPBA) by Estelle Herrscher at the 2001 American Association of Physical Anthropology meeting in Kansas City while studying in the USA. I had just completed a paleodemography course and studied the influential “Farwell to paleodemography” debate articles. JPBA’s immediate enthusiasm to meet a random French graduate student abroad completely surprised me. Later, I would discover that this curiosity was indeed one of JPBA’s genuine reactions as a true anthropologist when traveling and meeting people. This encounter was a formative moment in my curriculum. JPBA is one of the three researchers with Henry Duday and Jane Buikstra, who shaped my training and career, as well as my vision of science. After having kept a short correspondence with JPBA, he invited me to his office on the first week of my Paris return in September 2002. During this meeting, JPBA spent over an hour outlining what he could do to help me, even though I had never asked for anything. I was once again stunned by his generosity that I am still trying to emulate today. This chapter is my account of JPBA’s contribution to the Neolithic Demographic Transition (NDT) question during the seven years I have spent in his laboratory, on the other side of his office door. For more information on JPBA’s life, I will refer the reader to Hublin 2019 for an insightful necrology.

Theoretical framework

2JPBA had a robust understanding of cultural and biological anthropology and a solid experience in statistics, refined at the LISH laboratory in Paris (Hiernaux and Bocquet-Appel 1987) and later in the USA with Robert Sokal at SUNY-Stony Brook (Bocquet-Appel and Sokal 1989). JPBA principal research interest was focused on the understanding of human and pre-human population dynamics (fertility, mortality, and migration) from an evolutionary demographic perspective - the combination of a life history approach (the effect of natural selection on how organisms allocate their resources through the course of their lifetime), and optimal foraging theory (a set of evolutionary principles concerning the costs and benefits of daily resource choices), within a Malthus-Boserup demographic model (Lee 1986). He was a paleodemographer, and to my knowledge, the only one in France working within this theoretical framework.

3JPBA had a global approach to science. As a pragmatist, JPBA regularly argued with me that local narratives only clarified local behaviors and thus had limited explanatory power for our species as a whole. Rephrased in theoretical terms, JBPA was often more concerned about large scale ‘top-down’ approach by testing specific hypotheses derived from evolutionary theory; rather than the ‘bottom-up’ approach more common to the social science of demography, which seeks to explain a particular phenomenon (Blurton Jones 1986; Sear and al. 2016). However, JPBA always pleaded for a “common anthropological project” (Bocquet-Appel el al. 2017), defined as an interpretative system simultaneously rendering physical, physiological, psychological, and sociological variables. This vision is illustrated with regular contributions on a range of anthropological topics such as disciplinary knowledge (Bocquet-Appel 1989; Bocquet-Appel el al. 2017), history (Bocquet 1989; Bocquet‐Appel 1996), behavior (Hiernaux and Bocquet-Appel 1987), contemporary demography (Bocquet-Appel el al. 2002), statistics, (Bocquet-Appel and Sokal 1989; Bocquet-Appel and Bacro 1994), or genetics (Bocquet-Appel and Jakobi 1990; Bocquet-Appel 2012). JPBA was always grounded in empirical observations and used a dynamic interaction between data and theory to test hypotheses about larger anthropological questions. This process was never done blindly, randomly, or selectively, however. JPBA’s scientific honesty and desire to understand the data instead of massaging them to validate his intuitions were, as far as I am concerned, unequivocal.

The origins of agriculture: from the Neolithic Revolution to the Agricultural Demographic Transition

“[…] sedentism can set into motion a number of interrelated biological, behavioral, and psychological changes that can result in increased fertility and decreased child mortality, and an increase in the population growth rate, even if such growth increases work efforts in the long term. The scenario we have outlined here, however, is speculative and requires testing against archaeological data.”
(Kelly 2013: 212)

4I wasn’t part of the genesis for JPBA project on the European Neolithic diffusion first presented at a Spanish conference in 2000 with his colleague M. Paz de Miguel Ibanez and followed by its companion publication in 2002. The subsequent articles on this topic regularly spanned the pages of Current Anthropology, from 2002 to the last summary of results in 2011, in addition to other articles and book chapters (see the NDT chronological bibliography at the end of the chapter).

5I want to emphasize that despite having been a seemingly solitary researcher who could lock himself up for days with a noise-canceling headset to pour over dozens of articles ardently, write algorithms or put together brilliant (if dense!) PowerPoint presentations, JPBA knew how to build interdisciplinary teams to solve specific issues. For an illustration, see the acknowledgment of 23 specialists on the first page of the 2002 Current Anthropology NDT article or the large international teams funded by national or European grants afterward. Finally, when authors openly debated JPBA’s methods or results, these exchanges often inspired creative responses and ultimately promoted a more robust scientific approach that JPBA always welcomed, if only grudgingly (see the comments section in Bocquet-Appel and Naji 2006).

Demographic transitions

6Decades of archaeological research have been consistently supporting V. Gordon Childe’s hypothesis of a “Neolithic Revolution” (Childe 1925), describing a sharp increase in various archaeological features, including skeletal remains, with the transition from food procurement to food production and the advent of village life (Bellwood 2005; Bellwood and Oxenham 2008; Bocquet-Appel 2008; Hassan 1980; Kuijt 2009). Increasing site size or density of settlements was among the primary archaeological indicators of human subsistence changes and organization associated with the agricultural revolution (Price and Bar-Yosef 2011). This increase was a reflection of population growth as well as new forms of settlement and social organization. These Neolithic remains were most visible since they contrasted dramatically from the absence of archaeological record from hunter-gatherer populations.

7JPBA, among others (Binford and Chasko 1976; Cohen 1977; Livi Bacci 1992; Simoni el al. 2000), hypothesized that a demographic transition with an abrupt growth change was either the cause or the effect of the technological and economic shift and subsequent geographical expansion. This population growth was thus akin to a Neolithic Demographic Transition (NDT) in demographic European language (Bocquet-Appel 2002: 1). If we assume that any natural population lives in quasi-homeostatic equilibrium (Wood 1998; Bocquet-Appel 2002: 646), then this hypothetical increase in the birth rate entails that it was closely followed in time by a comparable increase in mortality, unless we assume a demographic growth rate that would rapidly reach a cosmic number (Bocquet-Appel 2002).

8This hypothetical two-stage NDT scenario mirrors the historical, contemporary demographic transition (CDT) well documented by historians and historical demographers (Caldwell 2007; McCaa 2002; Wood 1998). The industrial revolution created the economic and technological conditions for the initial stage of a rapid mortality decline with the advent of modern sanitation, the demonstration of germ theory, and the invention of the vaccine, among other discoveries, starting in the 18th c.in North-Western Europe and still happening today in some areas of the world (Caldwell 2007). Because fertility rates remained unchanged for several decades, the mechanical outcome was an unprecedented increase in population size via an accelerated growth rate. The second fertility stage was a comparable drop in the birth rate when populations started to adopt various effective birth control strategies to cope with the rapid increase in children to feed as a tradeoff between quantity and quality of offspring - JPBA always referred to Dickens novels for very poignant descriptions of what was happening in England during this industrial “baby-boom” - Once a population reached a homeostatic equilibrium, the growth rate would stabilize and oscillate around a demographic regime of low mortality and low fertility that most industrialized countries are experiencing today. As JPBA outlined in 2005 (Bocquet-Appel 2005), the drop of the birth rate below population replacement level is ongoing in correlation to some countries’ positive economic growth rate (fig. 1), and as access to education increases (fig. 2), among other factors.

1. Children per woman (total fertility rate) by Gross Domestic Product (GDP-in dollars) per capita.

2. Fertility rate vs. mean years of schooling.

9This contemporary low-pressure system of fertility and mortality is in stark contrast with the preindustrial farming regime also well documented as far back as the 17th c., and more sporadically from older medieval or antique accounts (Lee and Anderson 2002; Séguy and Buchet 2013b; Wood 1998). Pre CDT populations with high-birth and high-mortality rates experienced a typical growth rate of about 0.2 to 0.1% per year. The lack of data for older periods, and certainly for cultures with no written records, left most specialists to hypothesize that this demographic regime had been the norm for all pre-CDT populations outside of a few isolated forager groups, probably since the invention of agriculture and perhaps even before (fig. 3). However, since direct demographic variables were out of reach using standard archaeological evidence, the preindustrial demographic regime’s origin was never directly documented or measured (Cohen 1977).

3. Schematic changes in the birth (gray) and death (black) rates from hunter-gatherers (left) to modern time (right).

Demographic proxy indicator of fertility

10Paleodemography has been fraught with methodological biases and misconceptions almost from the start. Nevertheless, because archaeological evidence from skeletal samples is the only direct way to observe mortality/fertility patterns of populations with no surviving records, each skeletal assemblage becomes a critical piece of the human demography puzzle and requires direct investigation whenever possible (Kelly 2013). I will not describe the development of JPBA’s initial focus, alongside Claude Masset, to solve the deadlock that anthropologists and paleodemographers were facing since the fifties with skeletal age estimation (Bocquet and Masset 1977). I will refer the reader to another series of seminal articles (Bocquet-Appel and Masset 1982, 1996) and detailed historical summaries of the “Farewell to paleodemography” debate written by Frankenberg and Konigsberg 2006 and Buchet and Séguy 2013a, from the US and French perspectives respectively.

11Suffice to say that confronted with the inherent biases in anthropological age estimation methods, Bocquet-Appel and Masset developed several non-conventional demographic proxy indicators (Bocquet and Masset 1977; Bocquet-Appel and Masset 1982), ultimately resulting in the ¹⁵P⁵ ratio (Bocquet-Appel 2002). The ¹⁵P⁵ ratio (P) is calculated by dividing the number of skeletons found in a non-catastrophic (attritional) cemetery, aged 5 to 19, by the number of skeletons aged five and over. This ratio is highly correlated with the birth rate (adjusted r² = 0.963) and strongly correlated with the growth rate (adjusted r² = 0.875) in a stable population model (Bocquet-Appel 2002: table 2; Bocquet-Appel and Naji 2006: figure 6). This relationship describes a critical yet counter-intuitive correlation between funerary assemblages and life variables, rather than with mortality parameters as it was previously assumed (Johansson and Horowitz 1986; Harpending el al. 1990). This ratio was explicitly developed for archaeological investigations of funerary sites with taphonomic or ritual biases of children under-representation. Also, the cutoff age at death of 20 years could be safely estimated using anthropological standards (for an extensive critical summary, see Séguy and Buchet 2011 in French and 2013a in English).

Using a relative chronology to contextualize global patterns

12To test the NDT hypothesis on a large scale, JPBA developed a relative chronological framework (dt) to compare archaeological sites with different NDT absolute dates simultaneously (Bocquet-Appel and Paz de Miguel Ibáñez 2000, 2002; Bocquet-Appel 2002). With dt on the x-axis and P on the y-axis, the use of a loess fitting procedure is sensitive enough to track small variations of P (and thus of the birth rate) in multiple sites relative to the local introduction of the agricultural package (dt=0), in foragers (dt<0) or farmers (dt>0) groups (Bocquet-Appel and Paz de Miguel Ibáñez 2002). This approach was a conscious tradeoff between the lack of granularity on the map (e.g. scarcity of archaeological data, missing points in large geographical areas) and the statistical power to detect a signal at a large enough scale.

The demographic signature of an NDT

Europe and North Africa

13JPBA implemented the first test on a European and North African database with a skeletal demographic proxy and a relative chronological framework (for a complete description, see (Bocquet-Appel and Paz de Miguel Ibáñez 2000, 2002; Bocquet-Appel 2002)as well as Dubouloz and colleagues in this volume).

14The results described an average pattern for an NDT signature characterized by a noticeable increase in the proportion of immature skeletons during the forager/farmer transition corresponding to a growth rate increase from -0.3% to 1.3% (±1.07%) over 600 years. This transitional first stage of an unprecedented rise in fertility was hypothetically followed by an inferred second stage of mortality increase to reach homeostatic equilibrium in the new high-pressure demographic regime of high fertility and high mortality characteristic of farming communities until the 19th c. This signature was interpreted as mirroring the CDT in reverse order of demographic stages (Bocquet-Appel 2002: figure 3).

A Worldwide test of the NDT: North American and the Levant

15In his 2002 article, JPBA predicted that the NDT signature should be observable in all centers of agriculture inventions. At the time, the most likely candidate for skeletal data was the American continent. However, cemetery distribution and density were disparate at best, especially for South America. Also, for Mesoamerica and South America, the chronology of local domesticates’ adoption was not fully documented nor consensual (Piperno and Pearsall 1998; Smith 2006). JPBA hired me to go to the Smithsonian museum and the Library of Congress to access archaeological reports and build the necessary database to test the worldwide NDT signature hypothesis. This was the start of three years of uninterrupted contracts on the NDT project. Generous discussions with Bruce Trigger and Dolores Pipperno at the Smithsonian institution led us to focus our test on North America (present-day Mexico, USA, and Canada) to avoid unresolved debate about the origin and development of agriculture in the rest of the continent (Bocquet-Appel and Naji 2006).

16Results for the North American data indicated an increase of about 30% in the proportion of immature skeletons over roughly 500 years during the transition from forager to horticulturist-farmer populations, similar to the shift observed in European and North African (Bocquet-Appel and Naji 2006: 346, fig. 3). Of course, the dynamics of New World colonization implied a slightly different timing corresponding to local adaptations. The resulting discussions in the comments section (Bocquet-Appel and Naji 2006: 350-355) motivated JPBA to consider ethnographic data of transitioning forager groups to integrate total fertility rate estimates to evaluate fertility variations at the time of the transition (see below).

The Harvard symposium on the ADT

17With two major agriculture centers describing a comparable pattern of an abrupt increase in population’s growth rate at the onset of the NDT, JPBA started to reach out to the larger community specialized in the agricultural transition and consolidate the evidence from various lines of evidence. The Harvard symposium was co-organized and hosted with Ofer Bar-Yosef to present the outcome of this global outreach. The results were published in 2008 in an edited volume, “The NDT and its consequences” (Bocquet-Appel and Bar-Yosef 2008), bringing together archaeologists, zooarchaeologists, biological anthropologists, and paleodemographers.

18During the symposium, we presented the third test attempted in the Levant region, with Emma Guerrero’s help, at the time specialized in Levantine funerary archaeology. Levantine cemeteries revealed an increase in immature skeletons as high as in the rest of Europe but for more than 2000-2500 years, three times as long as the 600–800 years found in the Northern hemisphere (Guerrero el al. 2008).

Multiple lines of evidence

19JPBA relative framework benefited from combining multiple lines of evidence to test the tempo and magnitude of variables relative to the NDT. The first implementation of such a comparative test was done in 2003 with Jérôme Dubouloz. In two articles (Bocquet-Appel and Dubouloz 2003, 2004), the authors compared the evolution of the temporal distance of Neolithic enclosures site density from the start of the “Neolithic” way of life in Europe (for a summary, see Dubouloz el al. this volume). The analysis revealed that the sample of 700 sites varied quantitatively according to the demographic transition detected in cemeteries. The phenomenon reached a peak about 500 years after the transition of a given region for the anthropological data and about 600-900 years for the enclosure data. Similarly, the Levant’s gradual increase in archaeological site size was concomitant with a gradual decrease in gazelle remains (the primary protein source for local hunters) over a similar length of time. This trend supported the hypothesis of a slower tempo of change in the center of agriculture invention (the Levant) compared to secondary transition zones (Europe and North America; Guerrero el al. 2008: figures 3 & 4).

20In addition, the second mortality stage of the NDT is theorized to have been related to increases in regional population density and the size of human settlements, in turn, produced by the rapid growth of the first stage. The increase in mortality in the second stage resulted in a decrease in the rate of population growth. This decrease was documented in a preliminary fashion using archaeologically measured population growth rates in three Latin American regions (Bandy 2008). Bandy’s data show that the decrease in population growth in the second stage, at least for the areas in his sample, took place between dt = 600 and dt = 800, a tempo that matches previous independent sources of information.

21Finally, we took the opportunity to test the model’s complementary predictions, namely the deleterious consequences of agriculture on human health. This hypothesis mainly stemmed from the biological anthropologist’s community (Cohen 1977; Cohen and Armelagos 1984; Larsen 1995; Cohen and Crane-Kramer 2007). We implemented the analysis in our North American database using three common paleopathological “stress indicators” as reported in the literature, in addition to sexual dimorphism, to test the evolution of their frequencies in cemetery populations along our relative chronological timeline dt (Bocquet-Appel el al. 2008). Results mimicked the ADT signature and supported the interpretation of biological stress during the shift of economy.

Interpreting the ADT

“Dramatic demographic changes can be related in a provocative manner to changes in fertility as conditioned by shifts in labour organisation and diet.”
(Binford and Chasko 1976: 142-143)

22Anthropologists of all theoretical backgrounds debated the interpretation of the archaeological evidence Gordon Childe had initially outlined, from global descriptions to local narratives, explained in terms of cultural or population diffusions. However, recent studies of whole-genome ancient DNA data have considerably shifted our perspective on decades of inconclusive debate on understanding the European spread regarding the demic expansion of farmers originally from southeast Anatolia (Isern el al. 2017). Regardless, the empirical data describes a common underlying process where several independent cultural centers developed and spread the use of domesticated plants and animals within a short (in evolutionary scale) window of time (Piperno 2018). Kavanagh el al. 2018 suggested that their hindcast model of population density during the ADT supports a common global factor named the “surplus hypothesis.” This hypothesis describes an increase in atmospheric CO₂ and temperature at the end of the Pleistocene that improved environmental conditions for successful plant cultivation and higher resource productivity. This led to human population density and the near synchronous emergence of domestication in the major centers of agriculture invention (Piperno 2018: figure 1).

23Once agriculture was in place, populations quickly densified and rapidly spread (again, on an evolutionary scale) to all geographical niches on the planet, from the initial Pleistocene expansion to the American continent’s historical colonization and remaining pacific islands (Bocquet-Appel 2005). However, the lack of archaeological evidence and robust method to directly test the tempo and magnitude of the origin of the agricultural demographic regime remained relatively unchallenged with few local exceptions (Binford and Chasko 1976; Ellanna 1990; Gomes 1990; Hitchcock 1982; Roth and Ray 1985). How could we explain comparable patterns in such diverse ecological environments, with so many different local narratives around the ADT time?

The relative metabolic load model

24The initial causal variable JPBA invoked to interpret the observed first stage (increased fertility) of the ADT was the reduction of the interbirth interval. The mechanism involves decreased breastfeeding and earlier weaning age that follows the decrease in residential mobility and a greater reliance on stable food sources (Bocquet‐Appel 2009). Mechanically, the second stage (increased mortality) of the ADT, necessary for the return to a homeostatic equilibrium, was the consequence of increased sedentism with the accompanied development of zoonoses, infectious diseases, as well as the lack of sanitation in nascent fast-growing village life (Bocquet-Appel 2002: 647). Subsequently, the developing literature linking fertility (Henry 1961; McNeilly 1993) and energy expenditure (mobility and maternal energetics) in the relative metabolic load model (Ellison 2008; Valeggia and Ellison 2009) provided a broader theoretical framework to interpret the data in addition to the shift in food production alone.

25The observed signature of the NDT makes it possible to answer the question, was demographic pressure the cause (Boserup) or the effect (Malthus) of the cultural change? For JPBA, the population was simultaneously the cause and the effect of the cultural shift, which rapidly increased the population growth rate, locally or regionally (Bocquet-Appel 2008; Bocquet-Appel and Naji 2006). The cause is linked to the pressure on the hunter-gatherer production system’s carrying capacity, and the population increased probability of a system shift. The consequence can be understood by the rapid growth towards the new carrying capacity of the horticulturist-farmer system as soon as the new economic system is introduced, as illustrated by the resulting fertility explosion. This self-catalyzing process triggered the geographical expansion (e.g. individuals, nuclear families, demic) from the centers of the agricultural invention to the peripheral zones of adoption, conforming with the predictions of the Malthus-Boserup demographic model (Lee 1986; Wood 1998).

26Finally, the apparent paradox of health decline with increased fertility after the NDT should also be seen in the broader framework of nutrition and maternal care. The forager system sustained a very low demographic density (Bocquet-Appel el al. 2005) apparently qualitatively better nourished, but the system was fragile to stochastic environmental fluctuations. The hypothesis is that the tradeoff between offspring quality and offspring quantity could account for the combination of increased ill-health with more successful recruitment during the transition (Lawson and Borgerhoff Mulder 2016). Also, Quinlan’s (2007) cross-cultural analysis found that maternal care increased with increasing pathogen stress then declined. Overall, improved infant survival and greater reproductive success can still be consistent with poorer health and lower life expectancies for the population (Pennington 2001). In summary, the ADT is the positive effect on fertility of a relatively abrupt change in maternal energetics that occurs mainly during the transition from a mobile forager economy to a farming economy in any period (Bocquet-Appel 2011: S502).

Exploring pre-agricultural “natural” fertility

27Building on this hypothesis of population growth with the advent of agriculture, JPBA became more focused on the demographic variables before this transition. Demographers refer to populations not influenced by modern medicine and effective contraceptive as following a “natural” fertility and mortality schedule, including all groups before the invention of agriculture and, to a certain degree, contemporary pre-farming nomadic food collectors. Few data exist on natural fertility for Pleistocene populations. The only proxy demographers have been using are contemporary groups defined by their subsistence strategies as Hunter-Gatherers, Farmers, or Transitional (from Collectors to Producers).

28Campbell and Wood 1988 looked at 70 different populations and found that the average number of children from females surviving to mean childbearing age, represented by the total fertility rate (TFR), varies significantly from 3.5 to 9.8. This variation is more than three times the variance observed in “controlled-fertility” populations (TFR = 1.5-4.5). Wood concludes that: “there is no typical level of natural fertility” (Wood 1994: 32). However, other analyses identified a significant difference between agriculturalists (TFR>6.6) and non-agriculturalists (TFR<5.5) (Bentley el al. 1993; Blurton Jones 2016; Hewlett 1991). All these studies point out that hunter-gatherers do not necessarily have fertility as low as the level we see after the Contemporary Demographic Transition (Campbell and Wood 1988). Sellen and Mace 1997 tried to tease out these differences by distinguishing each subsistence strategy and relate them to fertility. They concluded that “differences in dependence on agriculture were the strongest predictors of the differences in fertility between closely related cultures” (Sellen and Mace 1997: 886). However, the main body of data for these contemporary groups is limited on many levels.

29The demonstration that these populations were free of any influence from agriculturist neighbors, or colonialist interaction, is inconclusive at best (for examples and discussions, see (Early and Headland 1998; Hill el al. 2007; Hurtado and Hill 1996; Kelly 2013). Also, there is a potential confounding factor in the availability of modern medicine and antibiotics as well as the rapidly expanding post-industrial culture, where sexually transmitted diseases had a significant impact on sterility and fertility rates (Pennington 2001).

30Besides, several ethnographic studies have documented the shift from mobility to sedentism specifically, with a subsequent increase in fertility (Binford and Chasko 1976; Ellanna 1990; Gomes 1990; Hitchcock 1982; Roth and Ray 1985). JPBA had directly tested the metabolic load hypothesis in the archaeological record (Bocquet-Apel and Naji 2006) and 172 ethnographic populations of North American Indians (Bocquet-Appel 2008: table 1). In both datasets, results supported the prediction that energy intake (diet) and energy expenditure (mobility and lactation) are good predictors of low fertility for female nomadic hunter-gatherers (high mobility, high carrying loads, and low-calorie diet) and high fertility for sedentary farmers (low mobility, no carrying load, and calorie-dense food). Also, when applied to 138 archaeological sites (Bocquet-Appel el al. 2008: 39), the use of the P ratio clearly differentiated nomadic hunter-gatherers (P=0.2228) from sedentary farmers (P=0.2536), with semi-sedentary shell mound foragers in between (P=0.2292).

31The main conclusion of this natural fertility analysis is the understanding that the ADT is a within-population shift. To detect the impact of the ADT, what needs to be compared is not the absolute values of the averages of fertility indexes between subsistence groups but the rates of change within those same populations when they experience an economic transition (Bocquet-Appel 2011).

Cabbages and Storks

32Following a series of articles with crafted titles (“Farewell to paleodemography” 1982, “Paleodemography, resurrection or ghost” 1985, “The Blind leading the lame” 2001), JPBA contextualized the outcome of the ADT project in 2011 with a “cabbages and storks” metaphor! In his last Current Anthropology article, JPBA highlighted that the major difference between the agricultural and contemporary demographic transitions is that the ADT’s cause was unconscious, determined by the mechanical effect of the agricultural economy’s invention on maternal energetics. In other words, through natural selection, humans, like all animals, have a propensity to maximize their reproductive success given their local environmental factors, and the strategies for higher reproductive success are likely to spread at the expense of less successful ones (Bocquet-Appel and Degioanni 2013). On the other hand, the fundamental cause of the CDT was conscious, i.e., the will to control mortality and reproduction (Bocquet-Appel 2011). The Industrial Revolution emerged simultaneously as these two controls="true" on mortality and reproduction, each localized in a zone of the Western cultural space. However, it did not cause them: a correlation, not causation. With its high fertility and mortality, the agricultural populations’ demographic regime appeared 10,000 years ago with the mechanical impact of the farming system on the energetics of fertility. This regime started to disappear with the emergence of conscious post-Enlightenment control over demography during the CDT, leaving cabbages and storks with no further influence on human progeny (Bocquet‐Appel 2009: 659).

Expanding the tests

33Following the NDT signals’ publication twenty years ago, several researchers started to refine and expand JPBA signature method in other parts of the world. I will only mention a couple here. Notably, Kholer and Glaude (Kohler and Glaude 2008) tested the NDT hypothesis in the US Southwest. They identified a strong signal in the mid-first-millennium AD in most subregions, following by a few hundred years the introduction of well-fired ceramic containers, more or less contemporaneous with the first appearance of villages. Kohler and Reese 2014 followed up to reconstruct the NDT process in greater detail. They revealed an anomalously long and spatially variable NDT dependent on environmental conditions (dry vs. irrigation farming) that resulted in a two millennia process for farmers to reach the agricultural niche’s carrying capacity in the Southwest. Willis and Oxenham 2013 presented oral health data from Neolithic An Son in southern Vietnam. The authors observed a clear pattern of elevated rates for oral disease in the Neolithic followed by a marked improvement in oral health during the Bronze and Iron Ages. In light of local archaeological contexts, this pattern was interpreted in support of the NDT mechanism of increased levels of fertility during the Neolithic, followed by a decline in fertility during the subsequent Bronze and Iron Ages. Downey el al. 2014 expanded on the European analysis using the summed calibrated date probability distribution of radiocarbon dates from archaeological sites, which confirmed increased growth rates after the introduction of agriculture. They validated the use of ¹⁴C dates as a demographic proxy. When Lesure el al. 2014 analyzed the P ratio in over 6,700 pre-Hispanic burials in Mesoamerica, they suggested that the demographic transition and associated fertility rates rose gradually during both the second and the first millennia BC, probably because of the low initial productivity of maize. However, the authors departed from the strict relative chronological framework (dt), which may have influenced the results due to the lack of precise data on agriculture’s local shifts. More recently, McFadden and Oxenham 2018 were inspired by JPBA’s P ratio and NDT scenario and proposed an alternative index to estimate the rate of natural population increase from skeletal remains and applied the method to ancient Southeast Asian samples.

Wait...what about cementochronology?

34I couldn’t conclude without mentioning JPBA’s contribution to cementochronology, the analysis of seasonal deposits of cementum on dental roots, for age-at-death and season-of-death estimations on humans and animals (Naji el al. 2016).

35Since individual skeletal age estimation is a central variable for understanding populations demography, JPBA has been continuously trying to solve the challenges associated with age estimation methods in anthropology (Bergot and Bocquet 1976; Bocquet and Bergot 1977; Bocquet-Appel and Bacro 2008; Bocquet-Appel el al. 1980). Even though Bocquet-Appel and Bacro 2008 were amongst the first to offer a viable solution to unbiased collective age estimation (see also the later expansion by Caussinus and Courgeau 2010, JPBA was hopeful that cementochronology could yield significant result at the individual level. Once again, his intuition was well-founded.

36When cementochronology’s protocol was finally dusted off and robustly validated (Kagerer and Grupe 2001; Wittwer-Backofen el al. 2004; Wittwer-Backofen and Buba 2002), JPBA immediately supported Joël Blondiaux to validate the method in France (Blondiaux el al. 2006; Gabard el al. 2007). Consequently, the clear implication of this precise and accurate aging method boasting success rates above 90% (Naji and Koel-Abt 2017) convinced me to train with Blondiaux to include cementum analyses in my Ph.D. dissertation (Naji 2010).

37Motivated by these positive initial results, JPBA funded the first workgroup on cementum with Thomas Colard, Joël Blondiaux, and myself in 2010. This group will then become the Cementochronology Research Program during the first symposium on cementochronology organized at the AAPA in 2012 (Naji el al. 2016). Our group has since developed reliable protocols to promote cementochronology as a reliable and accurate method (Colard el al. 2015) and motivated several significant advances in cementum biology, protocols, and applications in anthropology. Cambridge University Press is publishing these results in an edited volume entitled “Cementum in Anthropology” (Naji el al. accepted). This is yet another legacy of JPBA. The most exciting area to explore demographic variables stems from noninvasive synchrotron 3D analysis (Le Cabec el al. 2019; Newham el al. 2019). This technology allows us to identify innovatively individual stress events (Mani-Caplazi el al. 2019; Newham and Naji, accepted) and potentially female fertility in the past (Naji el al. accepted).

Concluding thoughts

38The debate around the origins of agriculture is still open but seems to be closing rapidly. Between the recent contributions in evolutionary demography, expanding archaeo-botanical research, the development of metagenomic data, and the drastic increase in modeling complexity (see Dubouloz el al., this volume), speculations of the past are rapidly transforming into a robust theory. Local environment-specific narratives might elude us for a little bit longer (Piperno 2018), but the broader outline of our demographic origin is filling up steadily.

39The lack of direct skeletal evidence has logically favored a more recent heavy computational modeling trend to tease out causal variables (e.g. environmental, demographic, cultural) from the multiplicity of specialized archaeological datasets now available. For example, in 2018, an innovating hindcast model using newly available climate reconstructions and predictors of human density (residential mobility and resource ownership) in 220 foraging societies, discussed the role of demographic changes in the origins of agriculture (Kavanagh el al. 2018). The authors concluded that the potential for increasing population density was an essential enabling condition in all regions that developed an innovation that changed the course of human history (Kavanagh el al. 2018: 483; but see Weitzel and Codding 2016 for a different perspective). This result is fascinating, but I was surprised by the lack of references to the NDT debate that directly tested these exact predictions using a direct proxy of human fertility.

40On the other hand, other modelers have clearly acknowledged JPBA’s contribution. In his latest book, Shennan 2018 (2018: 2) singled out JPBA as a major contributor to explaining the processes involved in becoming a farmer using evolutionary demography within a Malthus-Boserup framework. Similarly, Henderson and Loreau 2019 established an ecologically driven theory of demographic change that uses resource accessibility as a proxy for socioeconomic factors. These authors explicitly used JPBA empirical data to fit their model and to combine multiple concepts to represent 12 millennia of past population dynamics through simple human-nature relationships.

41Even though I wouldn’t claim the prominence of JPBA’s hypotheses in paleodemography, these nonoverlapping trends in publications were always puzzling to me and seemed somewhat counterproductive. My point is not to naively expect JPBA’s publication to be systematically cited, despite the combined Google Scholar citation metric for JPBA’s NDT articles (around 1455 on 05/05/2020, see NDT bibliography below). Even if this contribution isn’t trivial in anthropological publications, this one metric still seems relatively low compared to JPBA’s 682 citations from his most cited article, “Farewell to paleodemography” (1982). In the English literature, articles such as “The osteological paradox” (Wood el al. 1992; G-index=1480) in biological anthropology, or Bellwood “First farmers: the origins of agricultural societies” (2005; G-index=1371) in archaeology, clearly have a wider audience. I fully recognize that JPBA had an unorthodox approach, often taking short-cuts exasperating data-driven archaeologists in particular. JPBA’s incisive logic and focused mindset created many “lively” debates. However, the lack of cross-disciplinarity on the origins of agriculture and associated demographic change, and the perception that specialists discuss past one another or deliberately ignore some contradictory body of evidence, seems to be a depressing illustration of confirmation bias and discipline’s conservatism.

42For some, JPBA was an outlier in the data cloud of anthropologists, too often dismissed for the wrong reasons. For others, as illustrated in the present volume and his international standings, his global vision of Anthropology and Research placed him far above the mundane and always above the boring. I would like to conclude by relating my last lunch with Jean-Pierre a couple of months before his departure. I was fortunate to spend this afternoon during which he could still behave in his usual busy manner and sharp wit. Even after confessing having calculated his (low) survival probability, he could still comment on various science news, institution gossips, and even express regrets for not pushing me more in my professional career! From my first introduction to our last meeting, Jean-Pierre Bocquet-Appel always left me with a feeling of generosity, passion for science, brilliance, and always humor. He is missed terribly.

43Farewell!