Eight thousand generations

We are a young species. Homo sapiens appeared around two hundred millennia ago in Africa. We know that life expectancy was much lower in the past than today. Virtually no Palaeolithic hunter-gatherers lived beyond the age of 50-55. The situation was even worse in the early stages of the Neolithic transition, when diets got poorer and contact with domesticated animals brought new diseases. The first farmers and breeders rarely reached the age of 45. There were many exceptions on the path to progress. Net of these variations (at the beginning of the 19th century, life expectancy was still under 40 in most of the world, mainly due to high infant mortality), let’s work on the basis of a single human generation every 25 years. This means that 8000 generations have passed since we were born in Africa. Not a single one more. We are talking about 8000 passages from mother to child or, if you prefer, 4000 relays from grandparents to grandchildren. Think of your grandparents, then your grandparents’ grandparents, and so on: after 4000 grandparents we are at the source of our species. According to geneticists, some 107 billion human beings, including the present eight, have succeeded one another on Earth over these 8000 generations. Not a single one more. In some respects, it’s rather moving. On the third planet of the solar system which, seen from afar, is a grain of sand lost in the cosmic chill, all human beings’ great deeds and misdeeds, all civilisations, wars, empires, sacred poems, magnificent cities, heroic deeds and cowardice, kings and commoners, saints and sinners, inventors and explorers, every loving couple, all youthful hopes and expectations, all the worries of all the mothers of the world, all this vibrant humanity has so far taken the form of just 107 billion individual lives. We will remember very little of most of these, from Julius Caesar to Napoleon. All others have been lost forever, like tears in the rain.

Evolution is a great relay race. This is the first message left by human generations. The original group of African pioneers who initiated Homo sapiens’s history consisted of no more than 80-100 thousand individuals. Like a medium-small town today. Going back through the generations, any two human beings taken at random in the world - a European and an Australian Aborigine, a Korean and a South African, any couple - definitely share a common ancestor from this group. We are all siblings, or rather close cousins. The founding population had a baggage of genetic variations which then, like the baton in a relay race, passed from one generation to the next, until today. The DNA of cell batteries, i.e. of all our mitochondria, is transmitted matrilineally to the extent of deriving from a single ancestral African female matrix. This is why 99.98% of all human DNA is shared. And this is why ’human races’ cannot exist: human genetic variation is too low, distributed evenly over the earth’s surface and almost entirely individual, rather than related to geographical origins. We are too young as a species and too promiscuous: there hasn’t been enough time for races to form. Yet a marvellous array of thousands of different peoples - a family tree of cultural, linguistic and religious diversity - sprang from this handful of Africans who later migrated to Eurasia, Australia and the Americas.  The founding matrix of evolution is unity in diversity. DNA passes from one generation to the next like Ariadne’s unbroken thread uniting us all through each of our lives. Nothing has been lost.

Now let us stride on into the present. The first Homo sapiens arrived in Europe 1700 generations ago: they had dark skin and generally blue eyes. Less than 500 generations have passed since we invented agriculture and animal husbandry - in multiple centres of origin across the Fertile Crescent, China, New Guinea, Africa and the Americas. There have been 200 generations since the invention of writing. European colonialist globalisation began 20 generations ago. The industrial revolution has been a nine-generation affair. The Great Acceleration, i.e. the spike in all of humanity’s environmental impact curves (population growth, greenhouse gas emissions, biodiversity reduction, water and soil consumption, cement, asphalt and plastics production, the first atomic bombs, and so on), began in 1945, three generations ago. And at this point something unprecedented happened, in human and natural history. What is known as the Anthropocene. At the beginning of the 20th century, the weight of all human artefacts - i.e. the utilitarian objects bound up with our industrious everyday lives - accounted for 3% of the earth’s biomass, i.e. of all microbes, plants and animals combined. In 2020, ’anthropogenic mass’ was on a par with biomass. This had never been the case in the previous 8000 generations. At the beginning of the 20th century there were 1.6 billion of us and life expectancy was 50 years of age only if infant mortality was excluded from calculation. As of November 2023, there are eight billion of us. Life expectancy in some countries is over 80 and in many others over 70 (although in several African countries it is still just over 50). Thus, the Great Acceleration has also coincided with another absolute novelty: for the first time five generations are coexisting, starting with the generation born between the two world wars and ending with those who saw the light of day in the 2020s. The novelty is not simply a quantitative matter. Cohabitation between grandparents and grandchildren and thus three generations, is common in the natural world.. In the evolution of the Homo genus, around one million years ago, a new social custom emerged in the ancestors common to Homo sapiens and the other human species we have coexisted with (the Neanderthals and Denisovans). The fossil record is faint but crucial: individuals who were ’elderly’ for the period, even as old as 55, were found to have survived for years without teeth. Their fellow group members chopped or chewed the food for them and gave it to them, every day. Not letting the weak die was a revolution. The secret of human evolution is co-operation. A simplistic version of Darwinian theory predicted that older individuals, having fulfilled their reproductive function, would be left behind by natural selection.

But one fact was not taken into account: grandparents can contribute to the care of grandchildren, relieving busy parents of survival tasks and, above all, passing on a wealth of invaluable hunting experience, environmental knowledge and manual skills. This is why, as well as an emotional obligation and an act of solidarity, caring for the old was an essential benefit. Even among orcas and other cetaceans, grandmothers educate their grandchildren. This process implies that each generation leaves the next a positive heritage, but the Great Acceleration is changing the cards on the table. Over the last three generations the environment has been impoverished to such an extent that the legacy we leave our successors is threefold: our genes, as always, and our ideas and culture but also the environmental changes we have brought in, which posterity will have to adapt to. For a time the Great Acceleration’s balance sheet was a positive one: greater wealth and prosperity for part of humanity. Poverty, hunger and infant mortality have diminished, in absolute terms, and life expectancy has increased thanks to advances in medicine, welfare, hygiene and nutrition. But there was a hidden price in all this.

Homo sapiens has always been an ambivalent species. Wherever we went, we changed the world. Then we had to adapt to the world we had changed. The game worked well, but now it is in danger of blocking. In these five generations living together, for the first time ever what the third generation is passing on to the fourth and fifth is no longer a legacy of knowledge and resources but rather an environmental debt. The environmental transition is moving forward too slowly and this means that the cost for our children and grandchildren to adapt to the environmental crisis will be higher and higher. When the success of a species leads it to pass down a burden to its offspring, this is referred to as an ’evolutionary trap’. This is where we are now. Our advantage, compared to other species made extinct by overly drastic environmental changes, is twofold: firstly, we ourselves are the cause - not an asteroid or volcano - so we can reverse it if we want to; secondly, unlike the dinosaurs we know what is happening and cannot say that something just fell out of the sky onto us. Moreover, responsibility towards future generations is now enshrined in the Italian Constitution, after an Article 9 amendment was approved in 2022 (this is the first time since its promulgation, i.e. at the beginning of the Great Acceleration, three generations ago, that one of its fundamental articles has been changed) as well as a change to Article 41. Protecting the environment, ecosystems and biodiversity ’in the interest of future generations as well’ is now required by it. It is a far-sighted and courageous move, given that future generations do not yet exist. In his book Time and Water, Icelandic writer Andri Magnason recounts a conversation between his daughter, who is ten years old and was born in 2008, and her 94-year-old great-grandmother. The child calculates the year when she will be the same age as her great-grandmother: 2102. Then she calculates when her great-granddaughter, born in 2092, will be 94 years old: 2186. So Magnason’s daughter met her great-grandmother, born in 1924, and may meet her great-granddaughter, in 2186. A time span of 262 years which, Magnason tells his daughter, ’is your time and also the time of someone you will know and love, the time you will create. You can make a difference to the future until 2186’. Yes, our children will be able to do this, if they have enough vision. The builders of the ancient cathedrals knew very well that they would not see them finished. They knew that it was their grandchildren who would attend its inauguration, not them. But no matter: they laid the foundation stone all the same. It takes hope - the driving force behind Homo sapiens’ imagination - to think that a different future is possible. Mitigating global warming, preserving biodiversity, fighting against global inequalities: these are our transgenerational challenges. They are our cathedrals.