Cities are changing the way life evolves

The adaptation of living beings to the city has multiple effects on populations and ecosystems. A global study of white clover indicates that it acclimates to all urban habitats equally. This is clear proof that the human being is a dominant driving force in evolution.

Urbanization is increasingly transforming rural and natural environments in ways that Earth’s ecosystems and biodiversity have never experienced before. These changes alter the course of life, according to a study published in the latest issue of the journal Science.

The work, led by evolutionary biologists from the University of Toronto Mississauga (Canada), analyzed whether parallel evolution is occurring in cities around the world, thanks to the Global Urban Evolution Project (GLUE, for its acronym in English). .

A total of 287 scientists collected data from 160 cities in 26 countries. They collected 110,019 samples of white clover plants (Trifolium repens) –a cosmopolitan perennial with wide distribution– of 6,169 populations in its cities and nearby rural areas. The University of Seville and Almería are also participating in the study. However, in Spain there are no places of study, the closest collection was Lisbon in Portugal.

Adaptation itself is neither positive nor negative, it is simply a process that occurs as an adaptive response of the species to a stimulus. In this case, an increase in urbanization can lead to changes such as, for example, an increase in impermeable surfaces, changes in temperature or a decrease in the presence of herbivores.says Jose Raúl Román, a researcher at the University of Almería who, together with Miriam Muñoz Rojas, from the University of Seville, collected samples for the study.

Specifically, urbanization is causing many white clover plants around the world to produce fewer chemicals. “Decreases production of hydrogen cyanide (HCN), a chemical defense against herbivores“says Roman.

From this perspective, cities are a dominant force in the evolution of life on a global scale. From Toronto to Tokyo, Melbourne to Munich, white clover frequently evolves in direct response to environmental changes occurring in urban environments.

This knowledge could help conserve some of the most vulnerable species on Earth, mitigate the impacts of pests and diseases, improve human well-being, and contribute to the understanding of evolutionary processes.», argues the scientist.

life, evolution, species, pollution, cities, urban habitatWhite clover plants (Trifolium repens). /Nick Iwanyshyn


Important differences between rural and urban settings

The results show that the probability of a plant producing hydrogen cyanide increased by 44% on average from city centers, where the lowest values ​​were recorded, to more rural areas. Moreover, in 62 of the 160 cities studied, the production of HCN was less common in urban areas than in rural areas.

On the other hand, the study of the genome revealed that this evolution of phenotypic traits due to urbanization is explained by an adaptive evolution. “The results show that it leads to environmental changes that can drive rapid evolutionary adaptations on a global scale.», Asserts the expert.

White clover populations are polymorphic for the production of hydrogen cyanide, a chemical defense against herbivores that appears after damage to their tissues. This means that there are cyanogenic populations, which produce this compound, while it is absent in non-cyanogenic genotypes. This fact made it possible to study the transition from one genotype to another.

An unprecedented global collaboration

The research has created a huge data set that will be studied for years to come, its authors say. “Our collaborators have recognized the importance of this project. There has never been a field study on evolution on this scale, nor a global work on the influence of urbanization on evolution. It would have been impossible to do this without our group of collaboratorssays Marc TJ Johnson, co-author and researcher at the University of Toronto Mississauga.

Johnson also calls the project an inclusive science model. The team was divided equally between women and men and included not only senior researchers, but also students of all levels and from all inhabited continents of the world.

The Spanish team was not involved in coordinating the work, but Muñoz Rojas coordinates a global network, of which Román is also part, to discover the effect of land use changes on global microbial populations.

It is necessary to mobilize a large amount of resources, personal and economic, as well as to contact many groups, to establish very well designed and defined protocols so that all participants can carry out the collection”, explains the researcher from the University of Almería.


James S. Santangelo et al. “Global Urban Environmental Change Drives White Clover Adaptation”. Science


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