All species must have a certain variability between their populations and between the individuals that make them up. This variability, the product of past and present adaptation to different types of environmental conditions, is what guarantees future survival. The greater the diversity of forms and physiologies, for example, the greater the chances that some group of individuals will be able to survive any change or alteration in the conditions in which they live. It must be borne in mind that the loss of variability can be the first step towards the decline and extinction of a species and that each extinction, even if it is local, alters the functioning of the system of relationships in which each species operates and, therefore, increases the probability of collapse of the entire system.

This paper reviews the results of three decades of studies analysing the temporal evolution of the genetic diversity of more than 600 marine and terrestrial species well distributed throughout the tree of life. Considering that genetic diversity represents the variability of adaptations, the results offer a discouraging but expected panorama, given the known power of human action on the living systems of the planet we inhabit.

This exploration of published data concludes that the dominant trend is the loss of genetic diversity over time. A more detailed and exhaustive analysis also indicates that this loss of variability appears even in those species in which the existence of a decline in their populations had not been verified. Fortunately, the authors also confirm that conservation actions reduce the probability of loss of genetic variability although, once reduced, it is very difficult or almost impossible to recover that variability produced by the action of evolution over thousands of generations. If scientific data and empirical evidence should be the basis for planning the economy and political actions, this study contributes one more piece of information to the long list that supports the need for a change of course in our model of infinite growth and our crazy conception of development.

Biodiversity has been internationally recognized at three different levels: ecosystem diversity, species diversity and within-species genetic diversity. Genetic diversity is crucial for the long-term survival of population and species, as it helps them adapt to future environmental changes, such as disease outbreaks. By compiling and analysing more than three decades of research, this study shows that genetic diversity is decreasing worldwide for more than 600 species from a wide range of organisms (animals, plants, fungi and chromists) and it is not exclusive to rare and threatened species. 

Genetic diversity can be lost due to population decline and fragmentation generated through human activities, such as habitat degradation, unsustainable harvest or introduction of invasive species. This research shows that these threats directly affect genetic diversity, not only species diversity. Authors highlight that conservation actions such as promoting population growth and connectivity between populations could reduce further genetic diversity loss or even increase it. 

This study demonstrates that genetic diversity loss is a reality and it is occurring at a broad scale to many species around the world. Genetic diversity accumulates over thousands of years, and once it is lost, it is very difficult to get it back. Therefore, it is urgent to target conservation measures to safeguard the genetic diversity in order to ensure adaptive potential of populations and species.

It is hard to deny that human activities are diminishing biodiversity. So much so that any one of us can name a species that is in serious danger of extinction or has already disappeared from the Earth. The problem goes far beyond specific, iconic animals such as the white rhinoceros or the gorilla, or considerably larger groups such as frogs or pollinating insects. This work shows that the loss of biodiversity associated with human action is evident when looking at all eukaryotes on the planet (i.e. animals, plants, fungi and chromists, or all living things except bacteria and archaea). Of the many ways in which biodiversity can be measured (e.g. by simply noting the presence or absence of a species at a given location or, instead, by counting the number of individuals of that species at that location), the authors have turned to quantifying genetic diversity. That is, they have reviewed tens of thousands of articles and chosen those that estimate how variable the DNA sequences of the species studied are. These diversity estimates also make it possible to compare these values over time. In this way, the authors have observed that the most important losses in genetic diversity have occurred in birds and mammals over the last 30 years and have shown that human activities are responsible for this negative trend.

Among several findings that suggest an uncertain future for living things on our planet, the authors show that there is still some room for hope. Firstly, because existing protocols for species monitoring are effective and make it possible to identify losses in diversity early enough to take action. Secondly, because conservation actions undertaken to preserve specific regions or organisms actually bear fruit. In other words, when the experts' recommendations are followed, it is possible to halt or even reverse the loss of genetic diversity. With the results provided by these researchers, we can therefore confirm that we know that biodiversity is in danger, that we know how to monitor it and that we know how to conserve it. Science has done its part but still calls for urgent action to save (at least part of) the fabulous diversity of life on Earth.

This study published in the journal Nature shows the general decline in the genetic diversity of natural species over the last thirty years. The genetic variability of populations is fundamental to their survival in the face of environmental changes, which is why current populations are more vulnerable to extinction than they were three decades ago. This is a global trend that affects all types of living beings analysed (animals, plants, fungi and algae). Moreover, this loss of diversity seems to occur across the board, even in the absence of clear ecological disturbance and even if conservation strategies are implemented. As the authors point out, this effect may be due to the strong influence of population size on genetic diversity, and previous studies have shown a clear trend of declining natural populations globally.

The article has some limitations due to the existing literature on which it is based: there is clear evidence of a lack of data for certain geographical regions (e.g. Africa and the Middle East), as well as a strong bias towards studies on vertebrate species, even though they are not the largest group of living beings. However, these limitations do not detract from the overall conclusions of the article, and collecting genetic data from natural populations is essential for effective conservation strategies.