Biodiversity loss causes extinction – reducing global inequity is key to stop it

Humanity has triggered the sixth mass extinction episode since the beginning of the Phanerozoic. The complexity of this extinction crisis is centred on the intersection of two complex adaptive systems: human culture and ecosystem functioning, although the significance of this intersection is not properly appreciated. Human beings are part of biodiversity and elements in a global ecosystem. Civilization, and perhaps even the fate of our species, is utterly dependent on that ecosystem's proper functioning, which society is increasingly degrading. The crisis seems rooted in three factors. First, relatively few people globally are aware of its existence. Second, most people who are, and even many scientists, assume incorrectly that the problem is primarily one of the disappearance of species, when it is the existential threat of myriad population extinctions. Third, while concerned scientists know there are many individual and collective steps that must be taken to slow population extinction rates, some are not willing to advocate the one fundamental, necessary, ‘simple’ cure, that is, reducing the scale of the human enterprise. We argue that compassionate shrinkage of the human population by further encouraging lower birth rates while reducing both inequity and aggregate wasteful consumption—that is, an end to growthmania—will be required. This article is part of the theme issue ‘Ecological complexity and the biosphere: the next 30 years’. 1. A sixth mass extinction: the context Five major episodes of mass biological extinction (sensu Jablonski [1]: those with at least 76% of species lost) have occurred over the last 550 million years (Myr)—that is, a rough average of one mass extinction pulse per 110 Myr across the Phanerozoic period, following the ‘Cambrian (biological) explosion’ [2]. By this measure, mass extinctions represent a rare phenomenon in the history of life. These major reductions in the biological richness of the planet have been triggered by natural cataclysmic phenomena. For example, the combined effect of global warming and oxygen loss driven by major volcanic activity that took place towards the end of the Permian period triggered the largest mass extinction in Earth's history—the Great Dying—some 252 Myr ago [3]. Similarly, the collision of the Chicxulub meteorite on what is now the Yucatan Peninsula of Mexico annihilated much of the predominant animal life of the planet, famously the dinosaurs (save for the ancestral lineage of the birds), approximately 65 Myr ago [4]. This has been a story of biological catastrophe and recovery, characterized by a long process of biological resurgence. This delay of biological revival has been shown to be complex and dynamic, and varies depending on a plethora of factors, including, for example, the evolutionary lineage, geography and the particular mass extinction. However, a common denominator of recovery is a delay of several million years [5–8]—an important lesson for humanity. On the other hand, a post-extinction tree of life evolves in a new configuration and becomes reconstructed with different terminal branches. For example, the truncated tree of animal life that remained after the Chicxulub meteorite crash became radically reconfigured. The diverse and often gigantic reptiles of the Mesozoic were replaced by a lineage of small-sized animals, the early mammals—a bestiary of dwarfed species that underwent a trajectory of expansion, diversification and colonization of all parts of the biosphere [9]. Another salient aspect of that bio-recovery is that over the last 100 Myr of planetary life, but particularly after the last mass extinction, a seemingly relentless trajectory of biological diversification (particularly on land) has occurred, with a dramatic, exponential buildup, leading over the 550 Myr of the Phanerozoic to a recent biodiversity pinnacle [10]. From an anthropocentric perspective, and relevant to our discussion here, three lessons stand out: (i) Earth's biological diversity does recover from mass extinction events, but this is a process that involves millions of years; (ii) the identity of the organisms that rise from the ashes, and the configuration of the communities and ecosystems they become part of, are very different from those of the ‘normal’ period before the extinction event; and (iii) we, as a species, have evolved just at a time in which the diversity of living companions is the highest in the entire history of life. Occurring after a shorter inter-extinction interval than the Phanerozoic average—indeed at about 60% of that average interval—there is now a clear signal of the start of the sixth mass extinction episode [11,12]. Furthermore, the cause of the sixth mass extinction is a very different type of cataclysm: expansion of one element of biodiversity to planetary dominance. In short, that is, expansion of the human enterprise—the explosion of the numbers of Homo sapiens and their domesticates and the near-instantaneous (in terms of geological time) burst of ecosystem altering and destroying technologies. That expansion has created a new geological epoch, dubbed the Anthropocene [13,14]. The term Anthropocene, meant to replace the formal, geologically accepted label of the Holocene epoch, encapsulates the consequences of humanity's activities on Earth's life-support systems. Indeed, humanity's planetary impact includes alterations of geological processes so profound as to leave stratigraphic signatures in multiple structures of the Earth's surface. These new structures are technofossils like plastics, metal junk, radioactive wastes and other synthetic material footprints [15]. Therefore, the term Anthropocene is increasingly penetrating the lexicon of not only the academic socio-sphere, but also society more generally (e.g. it is now an entry in the Oxford English Dictionary) and is useful for discussion of the sixth mass extinction. The Anthropocene includes a plethora of manifestations in terms of the activities of humanity and the translation of those into a variety of environmental repercussions [16]. The former are represented by a set of socio-economic variables underlying growth, including, for example, the growth rate of the number of vehicles, of fertilizer consumption, of water consumption, of the number of dams, of fast-food mega-businesses, or total world gross domestic product (GDP) (see magnitudes of change in [16]). The accelerated growth rate of these socio-economic variables is driven by an explosive human population growth, particularly in countries or regions of countries where the consumption of resources is inordinately wasteful. That is, civilization is living now under a syndrome of too many people, with those in ‘developed’ parts of the world consuming an unfair share of Earth's resources and all together using an unsustainable fraction of our planet's natural capital (defined by the Convention on Biological Diversity as the world's stocks of natural assets which include geology, soil, air, water and all living things; https://www.cbd.int/business/projects/natcap.shtml). Humanity in many parts of the world is overconsuming, writing cheques heedlessly on our biological resource banks and disregarding the declining balance of natural capital rather than living more frugally on its ‘interest'. The environmental translation of these socio-economic drivers includes the correspondingly accelerated rate of greenhouse emissions (carbon dioxide, methane and nitrous oxide), leading to climate disruption on land and in oceans. Such climatic disruption encompasses global warming, with dramatic snow- and ice-thawing from polar and high-elevation lands and consequent global sea-level rise, ocean acidification and increased frequency and intensity of extreme weather events (see [14,17]). Despite the active disinformation efforts of deniers (often sponsored by big corporations and special interest groups, in particular the fossil fuel industry; see https://www.climaterealityproject.org/blog/climate-denial-machine-how-fossil-fuel-industry-blocks-climate-action), climate change-related calamities do manage to make their way into mainstream media, including movies and documentaries. This is understandable, given the increasingly vivid, short-term catastrophic consequences on humans (and their infrastructures) around the world. However, this is not the only global environmental change of the Anthropocene. Land-use change, over-drafting of soils and groundwater, rampant terrestrial and aquatic toxification, the proliferation of invasive organisms (plants, animals and pathogenic microbes) and, especially, the intimately connected loss of biodiversity are also grave manifestations of the Anthropocene [14,18]. Here we are concerned with the latter, which is one of the most critical manifestations of the Anthropocene. Save for the ethically and ecologically unsound arguments of de-extinction advocates (see [19]), the loss of biological diversity is irreversible on a time scale of interest to humanity. The loss of biodiversity could ultimately become the most pervasive global environmental change our species will face, since all taxa that have disappeared from Earth will be gone forever. Biodiversity loss is both a cause and a consequence of global environmental change. Therefore, our destruction of the global biological richness on which we utterly depend represents an unprecedented threat to the existence of civilization that could even threaten the persistence of humanity.