Biodiverse planet. Last 4 billion years and next at least four, approximately. Since there has been life there has been biodiversity on the planet. Evolution was neither linear nor ethical, responding to other biological and genetic characteristics, as well as to the movements and migrations of the vital individuals of the various species, first from other kingdoms, then also plants, then also animals, increasingly conditioned by ‘invasiveness of some, from a certain moment onwards those humans, from a certain moment onwards (and above all) of us sapiens. Strong restrictions on global biodiversity occurred long before us (and mammals), scientists from many disciplines agree that there have been at least five major mass extinctions. Today it is underway the sixth, it seems that a lot depends on what we have produced and manufactured. Previously, no creature has ever altered life on the planet so much, and yet other somewhat comparable events have taken place, five of which were so catastrophic in nature that a separate category was created for them, the so-called “Big Five”. .
The dense essay that the excellent journalist of New Yorker and award-winning American writer Elizabeth Kolbert (The Bronx, New York, 1961) published in 2014, ten years ago, it was a notable worldwide success and caused much discussion on the topic, The Sixth Extinctiontext immediately translated into Italian: The sixth extinction. An unnatural story, Neri Pozza Vicenza. It comes out now at the beginning 2024 a second expanded edition (translation by Cristiano Peddis and Raffaella Vitangeli, page 395 euros 19). After a short prologue, the author structures the text into thirteen chapters, each of which follows the events in particular of a single species which is emblematic in certain respects (modern name and binomial scientific classification, from the amphibian Atelopuss zeteki and from Mammoth americanum to us Homo sapiens, the thirteenth chapter rewritten in 2023). The creatures she talks about in the first four chapters have already disappeared, they serve her to deal with the great extinctions of the past and the complex story of their identification, starting from the work of the French naturalist Georges Courier (1769 – 1832).
In summarizing some great events in the history of terrestrial life of the last five hundred million years (Paleozoic) lists the appearance of the first plants on territories (not aqueous or marine) and suffered the first extinction of the late Ordovician, approximately 450 million years ago. Then he focuses on the subsequent extinctions: the second (late Devonian), the third which also involves reptiles (end Permian), the fourth (late Triassic), the fifth and most recent which involves birds, angiosperms and dinosaurs (end Cretaceous) and, after which, in the last sixty million years, primates and anthropomorphic apes slowly appear, only at the end (recently) hominins and humans first and foremost in Africa (finally leaving us sapiens the only ones of their kind). Extinctions are nothing new, the great extinctions of the majority of very rare plant and animal species, the fingers of a hand. Natural/unnatural (in the subtitle) is a question of semantics, the author recently recalled: “human beings are obviously biological entities, but our technologies are not and it is our technologies that really cause this extinction event”.
The fifth chapter serves to begin the second part, on the present, declaring us “welcome to the Anthropocene” (it takes inspiration from the rare Dicranograptus ziczac): the increasingly fragmented Amazon rainforest, a side of the Andes cordillera subjected to rapid overheating, the outer rays of the Great Barrier Reef, these and other places studied and visited in person by the author to document and delve deeper into the field, reporting meetings with scientists and communities, in the awareness that she could also go elsewhere to find similar traces of the changes taking place. A chapter is dedicated to the death of organisms in every possible garden of every home. The epilogue of this re-edition (which contains other adjustments and revisions) was written today, ten years later, and updates research and checks for each of the places visited and for the overall data of the ongoing sixth extinction, in relation to which the demographic crisis of some rich countries has no impact. The photos, the final chronological sheet, together with notes, bibliography and analytical index are useful.
Sooner or later it will decarbonize, claims the author, corroborating her opinion with the comments of authoritative scientists, but perhaps it will be too late for many of the organisms we love. Kolbert assigns in several points a vital and decisive weight to collective migrations: settling elsewhere to survive as a species. Even more this is characteristic of sapiens: as far as we humans are concerned “it seems that none of the classic environmental limits nor geography they candiscourage migration.” In the eighth chapter (on the forest) he underlines how, due to global anthropic climate changes, a rate of tree migration is now calculable, albeit with a surprisingly wide range of specific ways, different speeds and heights, original replacements and replacements. The migration and “replacement” model would also have affected some species of the genus Homo, us sapiens gradually “replacing” some of the species with which we have coexisted in the last hundreds of thousands of years in European and Asian ecosystems. In this context (“The Madness Gene”, chapter twelve) we talk about both Neanderthals and Denisovans.
An absolutely unusual and radical transformation is therefore taking place on the planet. Under our wise eyes, hands, brains. After discovering underground energy resources, i sapiens have started a process that changes the composition of the atmosphere which, in turn, alters the climatic and chemical balance of the oceans. Some animal and plant species react by moving, they manage to migrate towards the two poles; others find themselves abandoned in ecosystems now with too little water. The rate of extinction is growing dramatically and the way life on the planet is structured is changing, a dangerous process for all biotic factors, it’s better for us to know and react too. Elizabeth Kolbert has, in the meantime, published other essays (for example here:), despite its name now being connected to the definition and confirmations of the ongoing sixth extinction (here).
Countless speciations and extinctions, adaptations and migrations have occurred over the long course of evolution. The last ice age it intensified about 3 million years ago, with the expansion of the ice sheet in the Northern Hemisphere. Since then, there have been periods of glaciation lasting 40 – 100,000 years, during which the ice sheets cyclically extended and retreated. Each of these periods involved extinctions of species or death of individuals and migrations of others. For climate cycles, today we are in an interglacial period within the Quaternary ice age (because ice still exists on the earth’s surface), during which, in the last 800,000 years, there have been (multiple) glacial periods and interglacial periods. The end of the last one, Würm, began the Holocene, during which (so far) the average temperature has fluctuated only one degree up or down. Today every tenth of a degree counts.
The last glacial period is over about 11,700 years ago, when a general retreat of the ice began, albeit with some phases of small recoveries (for example, Europe between the 17th and 19th centuries). Sea levels rose by around 100 metres, resulting in flooding over the previous coastlines and the submergence of already inhabited areas. In the medium interglacial period (6000 – 3000 BC), defined as an “optimal climate”, the enormous extension of the agricultural area and the greatest commercial and cultural exchange of land and sea took place in various parts of the globe, never happened until that moment, with the start of civilizations connected more or less at the same degree of latitude, between the 20th and 40th parallel north. As is known, all this has been scientifically reconstructed: there is a sort of latitudinal band with a wider and more stable human presence, obviously with changing borders towards the north and south. They cannot be drawn with a line on paper, they are not institutional boundaries. Climate variations and social events have often made us move en masse, however on the scale of millennia the central part and that entire band tell us a lot, even for the future (here in particular).
Even the subsequent collapse of many of those civilizations is always related to non-contingent climatic fluctuations. The set of biotic factors has balances that can be supported or counteracted and which Homo sapiens it is altering perhaps to the maximum possible. If we calculate the number of species that have become extinct due to human activities in recent centuries, we arrive at percentages comparable to those of the major ecological catastrophes of the past, the five great extinctions mass. The one produced by us would therefore be the sixth. Species that we don’t even know about are becoming extinct. The trend is very risky, since we know well that the quantity of species present in an ecosystem is proportional to that ecosystem’s ability to provide us with valuable services. Yet this whole process, although unique in evolutionary history, is also natural. We are profoundly altering our global ecological niche and should expect it to change its selective pressures on us in the future. Scientific studies in various fields and dissemination works have raised a serious and documented alarm on the enormous decline in biodiversity in progress, being more and better aware of it is an indispensable first step.
