The Authors
Tattersall
DeSalle
He works in molecular systematics, microbial evolution, and genomics. His current research concerns the development of bioinformatic tools to handle large-scale genomics problems using phylogenetic systematic approaches. Dr. DeSalle has worked closely with colleagues from Cold Spring Harbor Labs, New York University, and the New York Botanical Garden on seed plant genomics and development of tools to establish gene family membership on a genome- wide scale. His group also focuses on human variation studies, microbial genomics, taxonomy, and systematics. In particular, they approach tree-of-life questions using whole genome information. He also dabbles in Drosophila systematics.
What’s the matter with kids today?
Increasing longevities and the generation gap
Had you been born a Neanderthal, perhaps 50,000 years ago, you would not only have belonged to a species estimated by that point in its history to have comprised 25,000 individuals at most, but you would have had to have been extraordinarily lucky to have lived to the ripe old age of forty. Perhaps that doesn’t sound too surprising when you think about how poorly their technologies insulated members of the species Homo neanderthalensis from Nature’s vagaries, certainly as compared to us privileged humans today.
But it is much more alarming to consider that, as recently as 1900 AD, the world average life expectancy at birth for a member of our own species Homo sapiens was estimated at less than 32 years.
Of course, that figure varies vastly among human societies around the world, and it continues to be particularly affected by sometimes appallingly high rates of infant mortality.
Nonetheless it remains true that, in many societies of our slowly maturing species, prior to the twentieth century overlap between the generations was typically not a great deal longer than the minimum time required for each cohort of people to see its offspring through to maturity and to pass along to them its basic technological know-how. In turn this means that, at least in its in its more abstract sense, human wisdom has traditionally resided in the relatively small subset of individuals who, often independent of their other personal qualities, had the good fortune to be able to accumulate experience over relatively extended lifespans. Some anthropologists have gone on from this to suggest that the tendency of women to outlive their own reproductive periods (as well as their men), implies a “grandmother effect” that assumed significant importance in human evolution as post-reproductive female hunter-gatherers took over many economic functions from younger women, allowing the latter to care for more offspring.
The anthropologist Robin Dunbar once proposed that the largest human social unit within which behaviors can be regulated by simple peer pressure numbers somewhere around 150 individuals. Beyond that limit explicit rules, and often draconian penalties for breaking them, are required to keep society running smoothly.
But in the wake of the shift from itinerant to settled lifestyles that began to radically change the very nature of human existence some 12,000 years ago (a time when it’s estimated that a mere 1 to 5 million people inhabited the Earth), vanishingly few of us have ever lived in societies that do not amply exceed this “Dunbar number.”
What that implies, of course, is that we have very recently been required by our circumstances to introduce intrusive social controls that were basically unnecessary for most of the long period over which humans evolved.
And the ready emergence of such mechanisms dramatically illustrates the unprecedented flexibility of human behavioral responses to new situations.
Initially, the astonishing expansion of the human population following the agricultural revolution was due to economic and pragmatic factors that both demanded more labor to till the fields, and that allowed each woman to care for more children.
But the breathtaking recent upward inflection in the world population, from 1.6 billion in 1900 to some 8 billion today, is more closely related to a recent and relentless increase in the average human life expectancy due to advances in sanitation, medicine, and agricultural productivity.
Such advances have apparently not done much to increase the maximum human lifespan, which seems to be remaining pretty stable at around 120 years.
But they have very clearly assured that the average person today will live substantially longer than his or her recent ancestors ever did.
And perhaps the most eyebrow-raising result of this change is that, as the United Nations has reported, the number of centenarians worldwide has recently increased dramatically, from about 150,000 at the turn of the millennium to almost 600,000 in 2020.
By one estimate, within the next few decades fully half of the human population will likely make it to a hundred years old; and an increase in average longevity of this kind, if sustained, will have huge demographic implications.
Among those implications is that, for the first time, the average citizen in the developed world will have a very good chance of living to meet and influence his or her great-grandchildren, and even great-great grandchildren.
How many of those overlapping future generations will occupy the same households is less certain, not least because while in the recent past maturing children in most economically advanced societies have tended to move away from the family home as soon as possible, the skyrocketing costs of housing in many such societies have recently brought this trend to a screaming halt.
The demographics of future multigenerational households are equally uncertain, as people marry at older ages (and indeed, more frequently not at all) and have fewer children.
Across the developed world, the average woman now bears 1.7 children in her lifetime, below the replacement rate and down from 2.7 in 1970.
Regardless of exactly how these trends eventually play out, there will clearly in future be more generations around to look after the interests of the youngest children in the family; and evidence already exists to suggest that, in multigenerational social units, grandparental help really does redound to the benefit of grandchildren. That advantage lies not only in help with the more formal aspects of education, but in the informal passing-on of personal experience and traditional cultural lore, an intangible but certainly significant social benefit.
But will the increasing generational complexity of families inevitably bring them together, or might it instead force them apart?
As every parent knows, the “generation gap” is a real phenomenon that develops as each generation tries to distinguish itself from the one before it; and it is a form of divergence that tends to be exacerbated by direct intergenerational contact.
Because of this distancing effect, it is possible that the coexistence of multiple generations in the same household, or even in reasonably close physical proximity, might also speed up the emergence of generational cultural disparities in food preferences, art, politics, linguistic expression, and myriad other features, via a ratchet effect that will assure that such differences persist.
Within cultures, that ratcheting might well work to encourage the expression of intergenerational disaffection, as in as the disillusion that is widely reported nowadays among members of Generation Z.