The end of the world as we know it: an analysis of evolutionary and cultural factors which may reduce future human survival

Abstract

At present, various national populations are now at different stages of the demographic transition. This transition may have far-ranging consequences for future humans. With the envisaged artificial support for human life, the significance of these non-metabolic processes may increase. Though the Earth is a thermodynamically open system receiving energy from the universe, the amount of energy flow is limited and the way its flow is structured on the globe restricts human development. Therefore, the future relationship between human population and the Earth may be constrained by a number of conditions; it may no longer be a simple conquest of the world by technology-wielding humans. Human cultures are still adapted to a world of high mortality, high fertility and little mass migration, where the structure and function of the human body was automatically adjusted by natural selection requiring medical intervention only rarely in cases of acute diseases or injuries. Moreover, human population may also continue to increase its “genetic load”, leading to a further decline in population fitness. This article will provide possible future scenarios for humankind from both evolutionary and cultural perspectives which may reduce long-term human fitness.

Keywords:

• human reproduction
• natural selection
• demographic transition
• Pleistocene evolution
• Holocene transition
• population explosion

Introduction: the current problem of human population dynamics

Humans, like any other living system, are thermodynamically open and can exist only when the energy flowing into their system is at least equal to that flowing out of the system. Since we live in a given natural environment, its carrying capacity (C), combined with our extractive efficiency (E) must provide the sum of energy/matter (S) that is needed to sustain human life: CxE ≥ S (Henneberg & Ostoja-Zagorski, 1984; Henneberg & Wolanski, 2009). In the past, it was relatively easy to apply this relationship because carrying capacity was largely independent of the extractive efficiency, while the sum of energy required to support human life consisted mostly of direct needs of human bodies (Henneberg & Henneberg, 1998; Henneberg & Ostoja-Zagorski, 1984). At present, however, the relations between the three variables have become complex. Our extractive efficiency significantly changes the carrying capacity of the environment (vide ozone hole, industrial pollution, climate changes) while the changing carrying capacity enforces changes in extractive efficiency (vide limits to the use of fossil fuels enforcing development of alternative energy sources). The sum of needs that must be met now includes a very substantial component of energy use outside human bodies – transport, telecommunication, production and maintenance of infrastructure, shelters, clothing, and health all require mechanised labour that is derived from sources of energy operating outside the metabolic processes of our bodies.

With the envisaged artificial support for human life (Saniotis & Henneberg, 2011), the significance of these non-metabolic processes may increase. Though the Earth is a thermodynamically open system receiving energy from the universe, the amount of energy flow is limited and the way its flow is structured on the globe restricts human development. Therefore, the future relationship between the human population and the Earth may be constrained by a number of conditions; it may no longer be a simple conquest of the world by technology-wielding humans.

The size and age/sex structure of the human population is an important constraint on our future existence. These basic demographic descriptors are a result of complex population dynamics comprising mortality, fertility and migratory movements. Various national populations are now at different stages of the demographic transition. The first stage is that of high mortality and high fertility. It results in an age structure typical for the “population pyramid” – lots of young children, fewer adolescents, even fewer adults and a small number of elderly people. In the second stage, mortality is reduced first while reduction in fertility lags behind, thus creating large natural increases and the age structure with increasing numbers of older adults and elderly people, but still a broad base of children. In the final, third stage, fertility becomes reduced to match mortality. This limits natural increase and produces a square age structure where numbers of children, adults and elderly people are approximately the same. Reduction of fertility at this stage is artificially regulated via contraception and abortions while the need for children is a function of changing economy of families in an industrialised society. Adults devote more time to earning money away from home, while having reduced time to raise children. Child upbringing in an industrialised society becomes expensive; therefore, bringing another human being into the world becomes a financial burden for young adults who increasingly find themselves unable to afford it repeatedly. Some of the most developed economies find themselves, in the twenty-first century, in the fourth stage of demographic transition – the natural decrease due to severely limited fertility. At this stage, fewer children are born than elderly people die and the age structure becomes an inverted pyramid with narrow base of a few children and a wide top of adults and elderly people. Though the number of people in the world is still increasing today, this increase will stop and even be reversed by the end of this century (UN World Population Prospects, http://esa.un.org/wpp/).

The effects of the demographic transition on the human population in the future could be profound. Population increase was still rapid at the beginning of the twenty-first century due to many nations being in the second phase of the demographic transition, though increase in population size may create opportunity for more mutations to occur (Hawks, Wang, Cochran, Harpending, & Moyzis, 2007). The global gene pool could contain many more genes that are currently contained in the populations of developing nations. These nations are still going through the second stage of the demographic transition while the genes from populations of developed nations will become less frequent. The opportunity for natural selection may become severely curtailed as more and more national populations enter the third and the fourth stages of the transition. At this stage, premature mortality is practically eliminated (Saniotis & Henneberg, 2011) while severe levels of birth control remove any fertility differentials, especially with the increasing role of artificial reproductive techniques. For some time embryo and foetal (intrauterine) mortality may still provide some opportunity for natural selection to operate, but its effects may be different from those of earlier centuries, because they may result in retention of embryonic features into the adult life (Henneberg & George, 1995), or incomplete development of some body structures (e.g. spina bifida occulta, Henneberg & Henneberg, 1999; Lee et al., 2011; Solomon, Ruehli, Lee, & Henneberg, 2009).

Since Louis Pasteur's discovery of the causation of infectious diseases, great progress has been made in preventing those diseases through vaccination, antisepsis, hygiene, sanitation and the use of pharmacotherapies, prominent among them antibiotics. This led to the “epidemiological transition” (Omran, 2005) during which degenerative diseases came to the fore while infectious diseases largely disappeared. The use of antibiotics – relatively weak agents helping human bodies to eliminate pathogenic microorganisms – resulted in vigorous operation of natural selection favouring drug-resistant pathogens (Herzog, 1998). These, like the extremely-drug-resistant tuberculosis or drug-resistant syphilis pose new problems for public health and require a completely different approach to combatting emerging infections. Adequate solutions to this challenge have yet to be developed.

Among the degenerative diseases, malignant neoplasms pose the most noticeable problem. Their management with pharmacotherapies is only partly successful, while surgical interventions offer hope that is limited by a number of factors. Western bio-medicine is still far from a full understanding of carcinogenic factors in our environments, thereby reducing its ability to implement effective preventive strategies. With the clear prospect of a quickly ageing world population, the challenge presented to human existence by degenerative diseases may become a significant problem.

Human cultures are still adapted to a world of high mortality, high fertility and little mass migration where the structure and function of the human body was automatically adjusted by natural selection requiring medical intervention only rarely in cases of acute diseases or injuries. However, without regard to the future of humanity we may end up in a world of shrinking population sizes, full of elderly individuals riddled with degenerative diseases that can only be managed by procedures so expensive that no economy may be able to afford them. Children will be rare, and may in the future be regarded as novel. When they disappear, the Earth may return to its precarious dynamic balance with the universe.

Paradigmatic change from Pleistocene to Neolithic periods

Throughout the Pleistocene period, human population size (Ne) was very low, probably around a few thousand individuals. By using human mitochondrial DNA (mtDNA), Harpending and Rogers (2000, p. 362) estimate that human population was only approximately 10,000. Further estimates of Ne further corroborate this figure – 10,000–15,000 individuals (Harding et al., 1997; Takahata, 1993; Wall, 2003). Archaeological evidence seems to support the idea for a very low number of humans living during the Pleistocene period. Indeed, the human lineage had seemingly experienced a marked population reduction ever since its divergence from the chimpanzee lineage during the Miocene period (Chen & Li, 2001). This low prehistoric Ne has surprised various thinkers due to the very large range which ancestral Homo had available (Gabunia & Vekua, 1995; Swisher et al., 1994).

Apparently, extensive size range which offered wider resources was not the only factor for increasing human fitness over a vast time period. A major reason why human population remained at a very low stable level for nearly two million years was a very high rate of infant mortality, indicative of the demanding environment which Homo had experienced. Environmental factors were instrumental in downsizing the human population. For example, ancestral hominins experienced at least one major bottleneck due to climatic events. One of these events included the Marine Isotope Stage 6 (MIS6) (190,000−130,000 ka), causing major aridity in Africa. Sjodin, Sjostrand, Jakobsson, and Blum (2012) have speculated that the MIS6 may have reduced the human population to <2000 individuals. While other bottlenecks probably had occurred throughout the Pleistocene period, it must be presumed that ancestral hominins in different geographical regions showed various adaptive strategies that enabled them to survive.

Secondly, the hunting/foraging mode of production which was indicative of ancestral Homo inhibited population growth. It is difficult to ascertain the kinds of environmental conditions which ancestral hominins may have faced. While evolutionary psychology has discussed a great deal the Environment of Evolutionary Adaptation (EEA), much of evolutionary psychology is speculative in relation to the kinds of selective pressures and events which may have informed hominin evolution (Confer et al., 2010, p. 122; Lloyd, 1999).

In all probability, morphological changes which became apparent in early hominins such as Homo erectus, such as obligate bipedalism leading to reduction in pelvis, decrease in gut size (20–60%), changes to neural hormonal regulation and metabolic regulation of the brain, leading to more complex social structures and intellection than previous hominins (i.e. Homo habilis, Australopithecines), and protracted neoteny, led to human babies being born altricial and females needing assisted labour (obligate midwifery) (Aiello, 1997; Aiello & Wells, 2002; Aiello & Wheeler, 1995; Jolly, 2003; Snodgrass, Leonard, & Robertson, 2009).

From Homo erectus onwards, there were increasing body/energy trade-offs due to changes in subsistence (i.e. persistent hunting) which demanded high physical activity levels (PAL) which were considerably higher than previous hominins and pongids. Persistent hunting would have demanded an increase in brain derived neurotrophic factor (BDNF) which in turn may have further influenced the development of the hippocampus and prefrontal cortex – key areas associated with memory, decision-making and higher cognition, spatial mapping and emotional regulation (Mattson, 2012; Raichlen & Gordon, 2011). Such changes may have expedited social evolution and its demands for higher level cognition in early hominins, also leading to modifications in the development of neonates and extension of the adolescent period, thereby enhancing neuro-plasticity (Bogin, 2003; Tardieu, 1998).

More realistically, we may hypothesise that from a reproductive viewpoint, constraints in resource access, environmental and climatic change were instrumental in keeping human population at bay throughout much of the Pleistocene period. Moreover, the dangerous demands of pregnancy and parturition and the growing-up period of neonates (which have been well noted) would have contributed to very low Ne. In order to get some idea of the energy demands of maternal child-rearing in early hominins, it has been hypothesised that the average hominin mother from Homo erectus onwards may have carried her child approximately 3000 miles in the first 4 years of its life (O'Keefe, Vogel, Lavie, & Cordain, 2011; Panter-Brick, 2002).

This expensive maternal requirement may also have been a crucial factor in limiting family size as it was veritably impossible to carry, fend and lactate more than one child in such circumstances. Hence, birth intervals of approximately four years was probably optimal, as a period less than this would have been problematic for survival for the neonate and its older siblings due to limited parental resources. As Beise and Voland (2002, p. 518) state, “reproductive effort also involves cost, which is why natural selection cannot favour unrestricted reproduction”.

The advent of the Neolithic Revolution (circa 10,000 BCE) not only brought a different mode of production, but also gave rise to permanent settlements with increased sedentism. In stark contrast to the Pleistocene period, the Holocene period was marked by unprecedented population growth. While arguments continue as to the reasons why Neolithic people changed their mode of production from hunting/foraging to farming and animal husbandry (Locay, 1989; Olsson, 2001; Smith, 1975), increasing population size demanded not only a stable source of food, but a new social paradigm for controlling and managing individuals. While small hunter/foraging groups followed community-based ownership of resources and egalitarianism, farming/animal husbandry in much larger and sedentary groups demanded complex sociocultural systems for maintaining social order and population management. Food storage and distribution and resource protection, as well as changes in rules of rulership – from community to family based ownership (Weisdorf, 2005, p. 573), which promoted resource allocation – gave rise to social stratification and subsequent social inequalities.

Although early attempts at social stratification in early Neolithic societies were probably moderate in comparison to middle and late Neolithic cultures, this period set the trend for organising and disciplining individuals. Morand (2002) postulates that the Neolithic revolution evolved a different family dynamic in which adults disregarded hunter/foraging food sharing and supplanted it with “human capital accumulation”, enabling adults to invest more in the quantity and quality of their children (Weisdorf, 2005, p. 577). Consequently, children reflected a family's level of consumption and resource accumulation via their labour; in short, children became an invaluable family resource, ensuring family integrity, continuity and protection of family resources. Concomitant with this familial consumption model was a redefinition of females, from food foragers to “baby-makers”. While a female's role in procreation was also important during the Pleistocene period, her role as principal food forager was equally as important. However, as the female's role as food forager became redundant during the Neolithic revolution, her association with procreation became foregrounded. As stratified societies grew in the Near East, female reproductive power became increasingly monitored and controlled by a litany of rules, regulations, taboos and customs. With the advent of organised religions during the Middle Neolithic period, female reproductive power increasingly came under their purview.

By the time of the Mesopotamian and Indus civilisations (i.e. Sumer, Babylon, Assyria, Mohanjo-daro), human reproduction had become sanctified by religious dictum. This aspect is evident in the book of Genesis where God commands humankind to multiply and populate the earth with their kind. The anthropomorphism of Mesopotamia later on informed the Abrahamic religions which encouraged high fertility at the expense of ecology.

What is significant in this equation is the power of culture in shaping and contouring human reproduction. For Kaufmann (2010, p. 7), modern humans are counterpoised between the “religiously committed” who seek to maintain fertility at least to a replacement level, and the “population declinists” who are failing to reproduce.

This cultural polemics suggests that for many modern humans fertility is no longer regarded as a “sacred duty”. This is certainly indicative of many industrialised societies with steadily declining populations. Does this mean that human population will dwindle? Yes it does, at least in the industrialised world for the time being (Jensen et al., 2002).

Conclusion: Ehrlich's Caveat

The continuing role of culture is important here in defining and contouring human reproduction. Cultures have never been democratic, and have been built on a store of knowledge, much of it anecdotal or evidence-based. From the Neolithic period onwards, humans have tended to lack foresight, as evidenced by the Neolithic Revolution which from human health and ecological aspects were considerably detrimental (Armelagos, Goodman, & Jacobs, 1991; Diamond, 1987; Larsen, 2006; Robson, 2010, p. 283). Although Neolithic people could not have been aware of the long-term consequences of the first epidemiological transition, their societies informed the organisational and ideological patterns for future cultures, including systematic war, famine, marked social stratification, and centralisation of power.

It was the noted biologist Paul Ehrlich who in his seminal book The Population Bomb (1968) several decades ago recognised that human population size was threatening life on earth. While Ehrlich's alarmist rhetoric has been criticised, it did bring to the fore the problem of a species that had lost touch with the environment. Indeed, based on current research, human fertility in many industrial and non-industrial countries is declining, not increasing, in contradiction to Ehrlich's claims. Reasons for this decline include a dramatic increase in androgenic pathologies such as declining male semen quality, as well as a rise in testicular cancer, undescended testis and hypospadias (Bergström et al., 1996; Dolk, 1998; Irvine, Cawood, Richardson, MacDonald, & Aitken, 1996; De Mouzon, Thonneau, Spira, & Multigner, 1996; Jensen et al., 2002; Jouannet, Wang, Eustache, Kold-Jensen, & Auger, 2001; Menchini-Fabris, Rossi, Palego, Simi, & Turchi, 1996; Skakkebæk, Rajpert-De Meyts, & Main, 2001). There are speculative multiple reasons for this androgenic malaise (i.e. phthalates, PCBs, pesticides, xeno-oestrogens), which act as endocrine disruptors. In addition, sedentism and highly processed diets are contributing to “diseases of civilisation” (i.e. cardio-vascular disease, stroke, cancer, type-2 diabetes, hypertension). This cohort of diseases is significant for the current and future global health disease burden, since lifestyle choices are passed on by epigenetic inheritance (Furrow, Christiansen, & Feldman, 2011; Grossniklaus, Kelly, Ferguson-Smith, Pembrey, & Lindquist, 2013; Jablonka & Lamb, 1995; Jablonka & Raz, 2009; Kasturi, Tannir, & Brannigan, 2008). Although the sheer scale of this disease epidemic is beyond the scope of this paper, it does reaffirm Ehrlich's prediction that extant hominins lack internal mechanisms for abating “runaway” feedback systems. Ehrlich further contends that due to their evolution, human perceptual systems are unable “to equip the human species with the ability to detect gradual alterations” in the natural and cultural environments (Ehrlich, 2000, p. 327). Consequently, Ehrlich recommends the development of “slow reflexes” – a capacity for detecting short- and long-term problems. This is presently problematic, given the enormity of global disease health burden and human population size. Alternatively, extant hominins cannot revert to an ancestral lifestyle. So where does that leave us? Based on current realities, the human population may continue to increase its “genetic load”, leading to a further decline in population fitness. However, micro-evolution is a complex process, whereby human biological mechanisms may evolve ways for reducing and adapting to current pathologies (Rühli & Henneberg, 2013).