Knowledge of biodiversity is advancing faster than species loss

Human activity is impacting planetary biodiversity. The massive metabolism of the naked primate consumes resources (space, food, materials of all kinds) and releases byproducts (toxins, nutrients, organic matter) that directly or indirectly limit, impede, or hinder the lives of many other beings that make up the biosphere. The result is the Sixth Extinction, caused by a single, seemingly conscious species, about which we have insufficient knowledge in terms of its taxonomic impact. Organisms never before described, completely unknown, are becoming extinct. Some of these disappearances may be jeopardizing taxonomic categories above the species level, which would be especially serious. Sometimes what becomes extinct is not just a particular species, but a genus, a family, or even more. The jarabugo is a small fish, a highly threatened endemic cyprinid of the Guadiana basin, found only in a few locations along this Iberian river. This species, Anaecypris hispanica, belongs to a monotypic genus, and its extinction would result in two losses: the loss of the species and the loss of the genus itself. There are no other representatives within it. However, the Iberian barbel, for example, another endemic species exclusive to the same basin, belonging to the genus Luciobarbus, coexists in the Guadiana River with two other barbels of the same genus. Its extinction, irreparable as a species, would have fewer taxonomic consequences than that of the Iberian barbel because two other Luciobarbus species still inhabit this river (in addition to others in other areas, both in the Iberian Peninsula and beyond).

Wiens et al. observe that science, with the incorporation of new tools, new technologies, and sufficient budgetary resources, is rapidly expanding our knowledge of biodiversity, of the richness of life on Earth. This could generate the false impression of a slowdown in the mass extinction process that humanity has unleashed. Nothing could be further from the truth. Simply put, our knowledge of the richness of life is limited, and we only account for what is already known, which is itself demonstrably increasing. The authors of the article estimate that more than 700 new genera, more than 20 families, and more than 3 orders are described each year, always associated with the discovery of new species. In the case of the lower categories, this process is statistically partly dependent on accumulated knowledge: more genera are described from groups with more species, mostly arthropods. However, for higher taxonomic ranks—family, order, or class—descriptions are mainly made among the least known groups, usually microscopic marine organisms or host-dependent parasites.

Current estimates of the value of global biodiversity are 8.75 million species. A very significant implication of this important work considerably raises this figure. The accelerated rate at which different taxonomic levels are described, from species to class, should compel a revision of the calculations used to estimate planetary biodiversity, which would be far greater than the aforementioned estimate, probably tens, if not hundreds, of millions of species.

Given the much greater significance of the extinction of a higher taxonomic rank, Wiens et al. conclude their article by urging researchers to focus their efforts on describing the lesser-known biodiversity among the higher categories for which data is scarce, before their premature extinction. It will always be more difficult for well-studied orders or families to provide new benefits to humanity than for rarer ones. The loss of the Spanish snail would be, in some ways, more irreparable than that of the short-headed barbel, although neither should ever become extinct due to a species capable of anticipating the consequences of its actions.

The diversity of life is the result of evolution. For example, the geographical isolation of a population belonging to a species can, over time, lead to the emergence of a new sister species. As a result of this process, it is possible to recognise different hierarchies of biological organisation in living beings. These hierarchies are nested within each other, since all organisms share, a priori, a common ancestor. Furthermore, the highest hierarchical levels correspond to lineages that originated in earlier moments of evolutionary history and that, in essence, represent successful biological solutions to certain environmental pressures. An illustrative example can be found in insects. Currently, around 30 orders are recognised, grouping approximately 1,000 families. These families, in turn, include about 130,000 genera, within which around 1.5 million described species are distributed.

In a recent study, John J. Wiens and colleagues estimated how many new taxonomic groups above the species level are described each year. Their results show that most new genera belong to the group that accounts for much of the Earth's diversity: arthropods, such as insects, arachnids, crustaceans, and myriapods. However, when higher hierarchical levels, such as families, orders or classes, are analysed, the situation changes: many of these new groupings belong to microscopic organisms, bacteria and fungi, often associated with marine environments or living as guests of other organisms. It has long been suggested that the number of currently described species of bacteria and fungi, which barely reaches 180,000, could represent only about 1% of the actual total, or even a smaller fraction. When discussing the diversity of life, therefore, it is essential to talk about microorganisms. These tiny life forms, the oldest in the planet's evolutionary history, have an enormous capacity for evolution, colonise and permeate virtually all environments, and play a fundamental role as engineers in all of Earth's biogeochemical cycles. It is therefore not surprising that many of the new supra-specific taxonomic entities are being discovered precisely among bacteria and fungi.

If each organism can be understood as a unique and effective solution for life in the face of a specific set of environmental conditions, the main conclusion of this study is that the number of large biological solutions still unknown could be enormous. There is therefore a risk of losing part of this diversity before it has even been discovered, as a result of our growing and profound intervention in nature. Hence the importance of promoting comprehensive and standardised biological inventory efforts, accompanied by effective conservation policies.

Despite the global biodiversity crisis driven by human activity, this research offers an optimistic perspective on our understanding of the natural world. The study highlights that, in addition to losses, the tree of life continues to grow at an astonishing rate, thanks to the discovery of new species and the description of new higher taxonomic ranks, such as families, orders, or classes. In just five years, science has made significant progress, establishing 700 new genera each year and more than 20 families. This finding drives a paradigm shift, which proposes prioritising the identification and conservation of levels above the species. The aim is to preserve phylogenetic diversity and better understand the evolutionary history of life on Earth.

As the article points out, there is still a vast amount of biodiversity to be identified, especially in less studied groups, such as microorganisms or species living in less accessible environments, such as oceans or caves. This hidden biodiversity, which is not visible to the naked eye, requires urgent identification before it disappears due to human impacts. To date, the most widely accepted estimate puts the number of species on the planet at 8.7 million. However, the work of John J. Wiens and his collaborators suggests that this figure could be significantly higher. To confirm this hypothesis, the authors emphasise the need for greater effort in the description of taxa with phylogenetic support, requiring taxonomic rigour and consensus that will allow us to understand the true magnitude of life on our planet.