The Human Lifecycle

Is the Human Condition Fixed or Mutable?

The Human Lifecycle Past and Future

What walks on four legs in the morning, two legs at noon, and three in the evening?

Riddle of the Sphinx, 400 B.C.

All the world's a stage,
And all the men and women merely players:
They have their exits and their entrances;
And one man in his time plays many parts,
His acts being seven ages. At first, the infant,
Mewling and puking in the nurse's arms.
And then the whining school-boy, with his satchel
And shining morning face, creeping like snail
Unwillingly to school. And then the lover,
Sighing like furnace, with a woeful ballad
Made to his mistress' eyebrow. Then a soldier,
Full of strange oaths and bearded like the pard,
Jealous in honour, sudden and quick in quarrel,
Seeking the bubble reputation
Even in the cannon's mouth. And then the justice,
In fair round belly with good capon lined,
With eyes severe and beard of formal cut,
Full of wise saws and modern instances;
And so he plays his part. The sixth age shifts
Into the lean and slipper'd pantaloon,
With spectacles on nose and pouch on side,
His youthful hose, well saved, a world too wide
For his shrunk shank; and his big manly voice,
Turning again toward childish treble, pipes
And whistles in his sound. Last scene of all,
That ends this strange eventful history,
Is second childishness and mere oblivion,
Sans teeth, sans eyes, sans taste, sans everything.

As You Like It, Shakespeare, 1623

Did Oedipus’ tragic journey begin with his abandonment in infancy, or when he answered the riddle of the Sphinx? The moment Oedipus gave the answer “Man”, the city of Thebes was freed of its curse, and Oedipus was free to marry the queen. Blind to his personal destiny, Oedipus nevertheless understood how man’s fate is bounded by the stages of the lifecycle. Thus man crawls on all fours as an infant, walks upright in his prime, and uses a walking stick in old age.  

The stages of the human lifecycle have been differently enumerated and differently imagined in various cultures. Regardless of cultural assumptions about the extent and the phases of human life, all cultures have agreed that each life has a beginning and an end, progressing from one developmental stage to the next. Under the age-based system explained in the Manu Smrti, a Sanscrit text written between 200 B.C. and 200 A.D., the Hindu life span, estimated at one hundred years, is divided into four stages. Perhaps because the Manu Smrti contained instruction for high-caste Hindus (the dvija castes), the assumption of a hundred years was plausible.

The Hindu Life Cycle

1.     Brahmacharya, or student, ages 5-24

2.     Grihastha, or householder, ages 25-49

3.     Vanaprastha, or retirement, ages 50-74

4.     Sannyasa, or renunciation/ liberation (Moksha), ages 75-100

The Manu Smrti describes the duties an individual is expected to perform throughout his life. The Hindu lifecycle was, and is, premised on the acceptance of duties appropriate to different times of life. Hinduism comprises an arc of spiritual progress through the four fixed life stages. As psychoanalyst Erik Erikson put it, the Hindu scriptures are “platonic” in their view of the four stages: “they outline the eternal meaning of the preordained stages” of life. (Erikson, Ghandi’s Truth, 1969, p. 34)

In the West, the advent of Christianity presented the general populace, including the poor, with the Holy Family as object of worship and with memento mori artworks, reminders of the brevity of earthly life. Rituals such as baptism, marriage, and the last rites marked the stages of life indelibly according to their religious significance. The newborn Christ child was an object of devotion, but among the devout, the soul of an infant who died before baptism was said to languish in limbo.

From as early as the 12^th century, European culture illustrated the human lifecycle in art and portrayed it in writing as the ‘ages of man’ or the ‘ages of life’. “The ‘ages of life’ occupy a considerable place in the pseudo-scientific treatises of the Middle Ages,” (Ariès, Philippe, Centuries of Childhood, 1960, p. 18). Artworks depicting the secular occupations associated with these discretely demarcated life stages provided constant cultural reinforcement. Pictures called ‘steps of the ages’ showed figures standing on steps going from birth to death: “The repetition of these pictures, pinned to the wall next to the calendar and in the midst of every day objects, fostered the idea of a life cut into clearly defined sections corresponding to certain modes of activity…The division of life into periods had the same fixity as the cycle of Nature…” (Ariès, p. 25)

The Ages of Life

1.     Childhood, birth to age 7

2.     Puerilia, age 7 to 14

3.     Adolescence, age 14 to 21-30

4.     Youth, age 30 to 45-50

5.     Senectitude, or “gravity”, 50-70

6.     Old Age, 70-

Le Grand Propriétaire de toutes choses, Bartholomaeus Anglicus, 1556

(On the Properties of Things) 

In 1950, psychotherapist Erik Erikson revised the common schema of the seven ages of man so eloquently described in Shakespeare’s As You Like It. Based on his work with children and adults, Erikson conceptualized the lifecycle within a psychoanalytic framework. Erikson’s “Eight Ages of Man” correlates each stage with the social skills that develop at that time, and with social institutions that support those skills. As Erikson puts it, “Each successive stage and crisis has a special relation to one of the basic elements of society, and this for the simple reason that the human lifecycle and man’s institutions evolved together.” (Erikson, Childhood and Society, 1950, p. 250)

The Eight Ages of Man

1.     Basic Trust vs. Mistrust – Infancy; from birth to 15 months

2.     Autonomy vs. Shame and Doubt – Early childhood; 15 months to 2½ years

3.     Initiative vs. Guilt – Childhood; 2½ to 6

4.     Industry vs. Inferiority – School Age; from 6 to puberty

5.     Identity vs. Role Confusion – Youth or Adolescence; puberty to 20

6.     Intimacy vs. Isolation – Young Adult; 20-30

7.     Generativity vs. Stagnation – Prime of life to Midlife; 30-65

8.     Ego Integrity vs. Despair – Old Age; 65-

Of the various schemata for the human lifecycle, Erikson’s schema is notable both for its refined staging of child development, and for the way in which he formulates the developmental tasks of midlife to old age. The tasks of the last two stages of life in the Hindu schema involve separation from the constraining ties of selfhood, body, and community [Vanaprastha] and renunciation [Sannyasa]. The secular schemata of the West –– from ‘On the Properties of Things’ to Shakespeare –– detail the losses of old age. Erikson proposes tasks that presuppose social interaction, and relevance, for the last two life stages. Generativity, the central task of midlife, “encompasses the evolutionary development which has made man the teaching and instituting as well as the learning animal.” (Erikson, p. 266) Ego integrity, the central task of old age, involves becoming a follower of the society’s image-bearers as well as accepting the responsibilities of leadership. (Erikson, p. 268)

Erikson’s 20^th century formulation assumes the same lifespan as the Hindu version despite global increases in life expectancy between the codification of the Hindu lifecycle in the Manu Smrti and the 1950s. But something important has changed regarding the end of life. In Erikson’s formulation, life’s final stages are not primarily concerned with detachment from society and social institutions. Rather, the modern approach to the end of life is, in its positive iteration, a period of social engagement. The alternatives – stagnation and despair – are still present, but so are there possibilities of failure for the earlier life stage tasks. Though far removed from the radical assumptions about aging proposed by Transhumanism, Erikson’s eight stages concept mirrors a society where change, and potential, are in the air.

Credible forecasts of near-future events include a world average life expectancy exceeding 70 by 2020 (World Resources Institute), and in developed countries, an average life expectancy of 130 by 2030 (Ray Hammond, The World in 2030, 2007). In The Future of Humanity, philosopher Nick Bostrom lists as a sufficient precondition for Posthumanity, a world average life expectancy exceeding 500 years (Bostrom, 2007).

As life expectancy increases, what changes can we expect in the stages of the lifecycle, or as evolutionary anthropologists call it, human life history? Transhumanists appear to assume that life expectancy will be increased by extending the midlife and old age stages of the lifecycle, and biomedical research confirms this approach: between 2014-2024, the International Association of Biomedical Gerontology forecasts the achievement of comprehensive functional rejuvenation of midlife mice (report, 2004). In the light of these predictions, are we to assume that the latter stages of the lifecycle are elastic, while the early stages are relatively fixed? If so, what might be the consequences for society of a human lifecycle fixed through childhood, and radically extended from midlife on?

Infancy and Childhood

…for it is the nature of man that his growth to adulthood is slowe, and this stems from his very nobility and perfection, since the nobler man is than other creatures, the greater the toil of nature…around his maturation.

Ökonomik, Konrad of Megenberg, 14^th Century

We in the West are proudly overcoming all ideas of predestination. But we would still insist that childhood training can do no more than underscore what is a given – that is, in an epigenetic development fixed by evolution.

Ghandi’s Truth, Erik Erikson, 1969

Since at least the beginning of the historic era, infancy and childhood have comprised the fixed beginning of the lifecycle. Human infants from antiquity to the present day have reached the same developmental milestones. Children, likewise, have performed the same repertoire of developmental tasks throughout history. Historian Philippe Ariès has demonstrated that, in Europe, conceptions of childhood have varied from the Middle Ages through the 17th century. (Ariès, Centuries of Childhood, 1960) Yet even as artists depicted children as “little adults”, many medieval writers – and likely all medieval mothers – understood that childhood conformed to well-defined stages of development. (Shahar, Shulamith, Childhood in the Middle Ages, 1990) Thus our modern understanding of child development through the stage theory of an Erikson or a Piaget has its precursor in medieval thinking. The medieval stages of infancy and childhood show some variance in their time frames when compared to psychologists’ schemata, but the developmental milestones on which the stages are based – weaning, dentition, locomotion, talking, etc. – have not changed over the centuries or indeed, millennia.

It is a truism of human development that the crucially large brain size of the human and the uniquely long dependence of the human child go hand in hand. Was Erikson right then, in saying that the lifecycle stage of childhood is fixed by evolution?

In several of its adaptations, the human infant relies upon biological systems that predate the appearance of Homo sapiens sapiens on the scene some 50,000 years ago. Ethologist Melvin Konner found that, of 45 reflexes scored for European and Bushmen neonates, few had survival value for European infants. The Moro reflex, however, which could also be seen in infant monkeys clutching their mothers’ belly fur, still had a survival value for Bushmen neonates. (Blurton-Jones, ed. Ethological Studies of Child Behavior, 1972, p. 289) Recently, a team of neuroscience researchers at the Laboratory of Neuromotor Physiology in Rome has shown that human babies learn to walk using the same network of spinal nerve cells as rats, cats, monkeys and birds. According to neurophysiologist Francesco Lacquaniti, “locomotion in several species is…perhaps related to a common ancestral neural network.” The scientist explained: “During evolutionary history, nature didn’t scrap the old hardware. Instead it was modified and tuned to adapt to our needs.” (Lacquaniti, Francesco, "Locomotor Primitives in Newborn Babies and their Development," Science, November 18, 2011)

In his study comparing European children to children of the Zhun/ twasi of Botswana, Konner points out the comparatively strong selection pressure among Bushmen children during the first five years of life, given the high rate of infant mortality in non-technological populations. The infant, therefore, should not be viewed as a being that is developing into an adaptive organism. Rather: “The infant at every point in his development is an adapted organism.” (Konner, Ethological Studies in Child Behavior, p. 302)  Konner concludes: “In the West, selection pressures among adults and children have changed…we can perhaps influence behavioral evolution by understanding changing factors affecting species-specific human infancy.” (Konner, p. 302)

The human infant’s heritage of biological systems shared with other mammals and with other primates is indicative of the millions of years of evolution it took to give life to Homo sapiens, the species with the longest childhood. Yet if, as Konner points out, selection pressures among children have changed in some parts of the world (and selection pressures have changed again between the 1970s and 2012), does it become more plausible to think of infancy and childhood as perhaps mutable stages of the lifecycle?

Natural selection occurs in modern human populations, as can be seen in the over-representation of an immune variant of the prion protein gene versus non-immune alleles in populations at risk of the chronic degenerative disease kuru. The survival of immune individuals thereby leads to the over-representation of this genetic variant. Moreover, some scientists maintain that human evolution has accelerated since the rise of civilization some 10,000 years ago. Does the fact of natural selection operating on modern populations, and the possible acceleration of human evolution in the past 10,000 years, increase the likelihood that all stages of the human lifecycle, including childhood, may change in response to changing selection pressures?

We can look at this question retrospectively, and inquire into the evolution of the human lifecycle itself. The human lifecycle is unique as to both its length and differentiation into stages. Social mammals have a lifecycle consisting of three stages: infant, juvenile and adult. Man's earliest hominid  ancestors also had a three-stage lifecycle consisting of infant, juvenile and adult. Anthropologists posit a five-stage human lifecycle: infant, child, juvenile, adolescent, adult. According to behavioral scientists’ analysis of fossils, the evolution of the new life stages of childhood and adolescence occurred around two million years ago, after the appearance of Homo erectus.

“Big baby!”  “Why don’t you grow up?”

Common reproaches.

Why do humans take such a long time to grow up? The human’s prolonged dependency allows for an extended period of brain growth. Apes have rapid brain growth before birth, and slower brain growth postpartum. In humans, infancy and childhood are the stages in which the most rapid post-natal brain growth takes place. Compared with other primates, human newborns have very large brains in relation to their body size. This combination of large brains at birth, and rapid brain growth from birth through childhood, gives humans the highest brain to body ratio among primates.

Analysis of the skulls and pelvic inlets of hominid fossils reveals that, for hominids, a pattern of rapid pre- and postnatal brain growth became necessary once adult hominid brain size reached around 850 cc. An adult hominid with a brain larger than 850 cc would have to have had a much smaller skull in order to exit its mother’s pelvis, and would have achieved the remaining brain growth postpartum. (Martin, R.D., Human Brain Evolution in an Ecological Context, 1983) Australopithecus afarensis, an early hominid with an adult brain size of 400 cc, likely retained the three-stage lifecycle. To achieve the adult brain size of 442 cc, Australopithecus africanus may have needed a slightly lengthier period of brain growth prenatally or during infancy.

Next in the evolutionary sequence, Homo habilis, with an adult brain size of 650-800 cc, would have needed extended brain growth in the fetal, infant and juvenile stages. However, extending infancy, and thereby extending the period during which females were unable to reproduce, may have put a demographic strain on Homo habilis. There was another solution: the evolution of a childhood phase in the lifecycle of Homo habilis.  Thus, “Insertion of a brief childhood stage” – during which offspring would be weaned and dependent on clan adults for food ­–“into life history could have reduced the reproductive strain.” (Bogin, Barry, and Smith, Holly, "Evolution of the Human Life Cycle,"  American Journal of Human Biology,1996, p. 707) According to this hypothesis, childhood as a life stage is defined as the period following infancy when the youngster is weaned from nursing, but still depends on older members of the group for feeding and protection. (Bogin, Barry, "Evolutionary Hypotheses for Human Childhood,' Yearbook of Physical Anthropology, 1997, Vol. 40, p. 63) As hominids with increasingly larger brains evolved, then, the need for a new phase in the lifecycle – childhood – increased as well. Homo erectus, with an adult brain of 850-900 cc, would have likely required an expanded childhood stage to achieve adult brain size, and to provide its young with the high quality foods needed for rapid brain growth.

Anthropologist Barry Bogin considers the evolution of the childhood stage of the lifecycle more than 2 million years ago as perhaps the earliest feature of modern human growth. The childhood life stage allowed for an extended period of brain growth and learning, but that is not “why” it evolved. As Bogin states: “The evolution of childhood occurred because it provided reproductive advantages to the mother ­­– by weaning early, the mother was free to reproduce again, faster than any ape.” (Bogin, Barry, "Modern Human Life History: the Evolution of Human Childhood and Fertility," The Evolution of Human Life History, 2006, p. 197)

Should the hypothesis that childhood evolved among hominids change the assumption, derived from the view of childhood as a consistent stage during the historic era, that the early stages of the human lifecycle are fixed by evolution? Indeed, by taking the long view, we have explored a highly persuasive argument that the childhood stage was itself an evolutionary development, albeit one which ultimately led to human preeminence.

However, if we bracket the two earliest stages in the lifecycle – infancy and childhood – and compare them to Martin’s suggested variations in the pre-juvenile lifecycle of Australopithecus, Homo habilis and Homo erectus, it is clear that, viewed as a unit, the stages infancy-childhood comprise an unchanging timespan denoting the same set of developmental landmarks found in the early life of each sub-species. While childhood may have evolved as ‘recently’ as 2 million years ago, it has become a mainstay of human development. The signal importance of childhood in providing time for brain development may mean we must regard it as a fixed stage in the lifecycle, and a fixed attribute of human nature. The unchanging nature of the beginning of the human lifecycle thus contrasts with the Transhumanist project of extending the lifecycle, albeit from midlife to old age.

Changing the Lifecycle, Changing the Proximity of the Generations

The Child’s Toys and the Old Man’s Reasons

Are the Fruits of the Two Seasons.

Auguries of Innocence, William Blake, 1803

Yet modern ways of living and the experience of seeing many, rather than just a few tough and exceptional persons, reach old age could make one wonder whether Blake may not have meant to imply that old reasons even as toys can be a bit childish.

Toys and Reasons, Erik Erikson, 1977

Humans in developed countries may not reach the 130-year average lifespan by 2030 predicted by futurologist Ray Hammond. Nor may 21^st century society as a whole enjoy access to the life-extending biotechnology that such a lifespan implies. But even without the implementation of the Transhumanist project, the 21^st century will see significant demographic changes relating to increased longevity in developed and developing countries. According to WHO, in the last 40 years of the 20^th century, life expectancy rose an average of 23 years in the poorest 50 percent of countries, and 9 years in the richest 50 percent (Nugent, Rachel, and Seligman, Barbara, How Demographic Change Affects Development,Center for Global Development 2008). The World Resources Institute forecasts a global life expectancy of 70 by 2020 and 75 by 2045.

The rise in global life expectancy from 45 to 65 between World War II and 2000 can be placed in dramatic historic perspective: this gain over the past 50 years is greater than any gain over the past 5,000 years. (Long-Term Global Demographic Trends: Reshaping the Political Landscape, CIA report, July, 2001) Due to increases in life expectancy worldwide, then, there will be an aging crisis in the first half of the 21^st century resulting from unprecedented growth in the number and percentage of people in the 65+, and even 80+, age ranges. Due to falling birth rates worldwide, a shrinking cohort of children ages 0-14 will accompany the old age cohort. While the childhood life stages (infancy, childhood and juvenile; or infancy, childhood and school age) remain the same, there will be proportionally fewer children across the globe; because the later life stages have been extended, there will be more old, and old old, people proportionally.

This demographic pattern suggests that, as the old get older and more numerous, the needs of the shrinking childhood cohort may be overshadowed. In any case the generations of the oldest old and the youngest young will become attenuated. Young and old may be distanced from one another by their differing economic and political interests. Not all of those in the aging cohort will be grandparents, and of those who are, many may prioritize state pensions and medical care over childcare and schools. As Erikson suggests in Toys and Reasons, society’s experience of seeing many people age at once may offer a more doubtful perspective on the wisdom of the elderly than the past experience of seeing “just a few tough and exceptional persons” survive into old age.  

Taking into account the circumstances that can be expected to arise in connection with this near-future scenario, it may be possible to construct a realistic context for the more radical adaptations to the human lifecycle advocated by futurists.

Out of Africa: Human Adolescence

Since as far back as the Middle Ages, adolescence has been recognized as the life stage that begins with puberty and ends with adulthood. No doubt adolescence has been viewed differently in different times. Cultural historian Ariès points out that, before the 18^th century, French students of the same age might be referred to by the Latin terms puer (“pupil”) or adolescens (“teen-ager”). A fifteen year-old schoolboy is thus described as a bonus puer. (Ariès, Centuries of Childhood, p. 23) It is not surprising, perhaps, that teen-age boys and their younger peers, studying together at the same school, would not be distinguished by age. It would be more surprising if marriageable girls of fifteen were not seen to occupy a near-adult status. In any case, adolescence was included in medieval representations of the ‘ages of man’, and the author of The Properties of Things had no difficulty in defining adolescence as “the third age” after childhood and puerilia. He defines adolescence as the life stage ranging from 14 to 21 years of age, and sometimes 28 – a stage at which the person is big enough to beget children. If adolescents were underrepresented in Europe before the 18^th century, they came into their own in 20^th century America. In the age of rock music and The Catcher in the Rye, adolescence became a cultural preoccupation. Adolescent angst, long a literary trope, has recently been linked not only to hormonal changes at puberty, but to the plasticity of the adolescent brain.

Growth of the hominid brain may have been enabled by the evolution of childhood. Similarly, the evolution of the adolescent life stage appears to have given humans the opportunity to complete brain development before the individual is fully functional as an adult. We now know that human brain size increases through infancy, childhood, and even adolescence. So too, the development of brain structures and key neurological processes continue up to adulthood.

Increases in brain size up to and during adolescence have been measured using MRI imaging. These size increases include total cerebral volume, which peaks at 10.5 years for girls and 14.5 years for boys, and cerebellum volume, which peaks about two years later than cerebral volume. Grey Matter volumes peak in the frontal lobes at 9.5 years for girls, and 10.5 years for boys; in the temporal lobes at 10.0 and 11.0 years; and in the parietal lobes at 7.5 and 9 years. The corpus callosum, the structure joining the two hemispheres of the brain, increases in size during adolescence. So do White Matter volumes. Total cerebral volume and Grey Matter volumes peak between the ages of 10-20 years, making adolescence a key period for the growth of the brain.  (Giedd, J.N., "The Teen Brain: Insights from Neuroimaging," Journal of Adolescent Health, 2008, Vol. 42, pp. 335-343)

Due to the refinement of brain development during adolescence, two key areas of cognition differ sharply in adolescents and adults. Recent research has shown significant differences in the ways adolescents respond to rewards, and has demonstrated how these differences are underpinned by brain development. In addition, scientists have discovered neurological differences in the adolescent and adult prefrontal cortex, the brain’s control system. 

Advances in neuroscience and related fields have enhanced our understanding of the adolescent brain. We now know that not only is brain growth extended into adolescence, but so are the development of brain structures and biological information-processing systems. In particular, the brain circuitry for incentive processing is developed during adolescence. Data analysis from fMRI studies reveals that teen-agers do not use prefrontal regulatory systems as much as adults do when assessing risk. This and other distinctive adolescent behaviors regarding incentive processing correlate with diverse aspects of adolescent brain maturation. Age-related Grey Matter reductions through synaptic pruning of underused neural links, late maturation of the basal ganglia, and the continued maturation of the signaling network implemented by dopamine neurotransmitters: all take place during adolescence. (Geier, Charles and Luna, Beatriz, "The maturation of incentive processing and cognitive control," Pharmacology, Biochemistry and Behavior, 2008, doi: 10.1016/j.pbb.2009.01.021)

A well-known trait of adolescence distinguishes this lifecycle phase in humans from any comparable stage of development in nonhuman primates. Only humans achieve rapid growth of skeletal tissue – the growth spurt – between puberty and adulthood. The anthropological definition of adolescence thus characterizes the end of adolescence as the completion of the growth spurt, the attainment of sexual maturity, and the attainment of adult social and economic status.

Adolescence holds clear advantages for the human species, including the growth spurt and extended brain growth and development prior to adulthood. Why is it, though, that adolescence evolved as a stage in the human lifecycle? Barry Bogin states in his hypothesis on the evolution of the human lifecycle that adolescence evolved among humans to facilitate reproductive fitness. Citing a study of apes in the wild, Bogin points out that there is significantly higher infant mortality for the first- and second-born offspring of baboons, macaque monkeys, and chimpanzees. During adolescence, girls learn the maternal skills that lead to better survival rates for the first-born and second-born infants of hunter-gatherer people. (Altmann, J., Baboon Mothers and Infants, Harvard University Press, 1980) Boys, too, achieve reproductive fitness in adolescence, a time when they learn adult skills and, due to their immature appearance, avoid dangerous competition over mates with adult males. Adolescence is distinguished from the juvenile stage by the onset of puberty; however, there are important indications that adolescence is, by and large, a life stage that precedes mature sexuality. Bogin points out that girls typically have 1-3 years of anovulatory menstrual cycles following the menarche, while boys, though biologically mature at puberty, in fact rarely father children before the third decade of life.

Like childhood, adolescence evolved as part of the human lifecycle. There is evidence that it is evolving today, at a much faster pace. Children in the West have begun to reach puberty earlier, and in the developed world the need for higher education has prolonged adolescence, by delaying the time when most young people can take on adult roles and responsibilities. That this is a biological as well as a cultural shift may be attested by the fact that increases in IQ are now seen among adolescents spending more time in school. (Gopnik, Alison, "What’s Wrong with the Teen-age Mind?" Wall Street Journal, 2012) Adolescence, it seems, is a potentially mutable part of the lifecycle. Already covering a larger swath from puberty to adulthood, adolescence may thus be a candidate for further expansion in light of increased human longevity.

 

Modern Adolescence and the Youth Bulge of the 21^st century

In the West, then, adolescence has already become a moderately extended life stage, for both biological and sociocultural reasons. Training for the information age and delays in marrying and starting a family mean that adolescence lasts longer than it did even twenty years ago. Smarter and better prepared than earlier generations, adolescents in developed countries must nevertheless postpone entry into adult society. Among the reasons for postponement are not only the greater amount of time needed to acquire marketable skills, but the lack of economic opportunity once the young person does enter the job market.

Responding to the dilemma of delayed adulthood, psychologist Alison Gopnik points out that the “wide-ranging, flexible and broad learning” typical of high school and college may be at odds with job skills acquisition, and advocates giving adolescents more apprenticeship opportunities. (Gopnik, WSJ, 2012) Useful programs such as internships, however, cannot alleviate the central paradox of the new adolescence, a life stage during which young people are expected to prepare longer and harder for a weaker, more competitive labor market. Moreover, the economic competition the new adolescents will face is not just peer competition. Arrived on the job scene, they are likely to discover that somebody already has their job, and that somebody is a member of one of the older generations.

Adolescents in the West are part of a worldwide youth bulge. The youth bulge is the dramatic proportional increase of adolescents and young adults in the world population. While the age range in question is figured differently by different demographers, there is no disagreement among population scientists about the phenomenon itself. What demographers call the youth bulge is a striking development: the 1.5 billion 12-24 year-olds alive in 2008 represent the largest youth bulge in the history of the human population. While youth populations in Latin America and Asia may have peaked, the youth cohort in Africa and South Asia is expected to grow through 2050. (Nugent, “How Demographic Change Affects Development,” p. 12) The percentage of world population represented by 15-29 year-olds will decline by 2020 in Asia, but will extend beyond 2020 in the Middle East, parts of Latin America and Sub-Saharan Africa.  (“Long-term Global Demographic Trends,” p. 36)  

Will the Paradox of the New Adolescence Be Magnified by the Youth Bulge?

Demographers, who divide the human lifecycle into age ranges in order to study trends, are keenly aware of how the size and distribution of one age group in the population affects the fortunes of the rest. For the purposes of predicting population trends in the 21^st century, demographers have posited the following age ranges.

Age Ranges in Demographic Projections for 2001-2050

Infancy – 0-2

Childhood – 3-14

Youth – 15-29 {12-24}

Household-forming  Age – 20-39

Midlife – 40-64

Old Age – 65+

In the first half f the 21^st century, demographers predict that population bulges will occur in the 15-29 year-old and age 65+ cohorts. The household-forming (20-39 year-old) and midlife (40-64 year-old) age groups will be proportionally smaller through 2050. While some demographers see the youth bulge as an economic “window of opportunity,” this will only be the case if developed and developing countries are able to provide jobs for their young adult citizens. However, economic prospects for youth worldwide are linked to the overall age structure of the population. Fewer people in the household-forming and midlife cohorts means fewer tax-paying workers to support the young and the old, a situation that could lead to less productive economies. The expected decline in the percent of household-forming persons (a cohort which overlaps with the youth cohort) may have dire economic consequences in itself, as the household-forming cohort stimulates production in key economic sectors like construction, real estate and durable goods. (“Long-term Global Demographic Trends,” p. 25) A U.S. government study describes the possible political consequences of this population pattern: “when the cohort of 15-29 year-olds exceeds the 30 to 54-year old cohort by a ratio of 1.7 or more, a country’s probability of instability – defined as revolution, ethnic war, genocide, and disruptive regime changes – increases.” (“Long-term Global Demographic Trends,” p. 39)

The world population pattern envisioned for the first half of the 21^st century, comprising worldwide increases in longevity and prolonged, significant youth bulges, may lead to intergenerational conflict. The claims of childhood may be overshadowed by the claims of a large (and articulate) aging cohort.

What of the claims of adolescence and youth?  At the time of the First World War, “Awareness of youth became a general phenomenon…in which the troops at the front were solidly opposed to the older generations in the rear.” (Ariès, p. 28) The perennial complaint that “Old men make wars for young men to die in” sums up the lack of autonomy that has beset youth historically.

It is to youth, however, that the older generations must eventually give the responsibility of leadership. If there is to be no peaceful passing of the mantle, then violent succession becomes a possibility. In a CIA report published in the summer of 2001, the authors list several ways in which youth bulges may contribute to political instability, as defined above. The suggestion that youth bulges may, “Empower youth to slowly weaken authoritarian regimes in places like Iraq”, though in no way prescient, attests to the power of youth to bring about regime changes. Such changes took place during the Arab Spring of 2010, when uprisings fueled by discontented youth led to the eventual deposition of dictators in Tunisia, Egypt, Libya and Yemen.  (“Long-term Global Demographic Trends,” p. 40)

It is difficult, but possible, to assess global population trends over the next fifty years. Although demographers may err in making certain predictions, their description of the world population’s age structure  – with its aging crisis and its youth bulges – is valid. It requires a skill set very different from the one used in demographics to look at humanity’s more distant future in even a plausibly realistic way. In the investigation of humans from an evolutionary perspective, evidence from the behavioral sciences, fossil forensics and comparative anatomy must be interpreted with some speculation. Yet in our backward glance at the two million years comprising the emergence of Homo sapiens and his hominid ancestors, inquiry remains grounded in fact and testable by established methodology. Methodology hardly describes any current approach to looking at humanity’s distant future. The far future belongs to physics and astronomy; but where to locate man in deep time? Or the far future belongs to intelligent science fiction, the work of great imaginations whose human characters are archetypal as much as they are futuristic.

Dynamic organizations like the Future of Humanity Institute and the Singularity Institute are performing a great service by conducting research and opening science-based, informed dialogues on topics like global catastrophic risk and artificial intelligence. However, the philosophical or machine-learning backgrounds of the majority of participants in these conversations have led to perhaps a narrow set of assumptions about the human condition. A multidisciplinary appraisal of humanity in the light of evolution, the historic past, and the shaping of the human lifecycle, could infuse a greater degree of psychological realism into current projections of humanity’s future. Such an appraisal could potentially widen the field of inquiry concerning human enhancement, life-extension and uploading, and the relation of these phenomena to the human trajectory.