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Humanity is radically changing the dynamics of natural selection

We have known for a long time that human activity has an impact on fauna and flora, but a vast study has just demonstrated the extent of the phenomenon.

Everyone knows today that human activity has a huge impact on the various ecosystems of the globe. This is a fact already proven indisputably by countless studies, especially in the short and medium term; but we are still sorely lacking in hindsight to accurately estimate our impact on these particularly subtle dynamics. A large study identified by ScienceAlert has recently taken an interest in this question; his results suggest that humanity is not only modifying the direct environment of species. It also affects their long-term evolutionary trajectory.

Evolution is an excessively slow process that can only be studied over particularly long time scales. Life as we know it is the result of millions of years of mutations and natural selection; If current species are adapted to their respective environments, it is primarily because the constraints of their environment have pushed them to adapt to their environment or to disappear.

In the scientific literature, these constraints which condition the trajectory of a species are called “selection pressures”. They can take many and varied forms; it may be the availability of resources, competition with competing species… and, for several centuries, the influence of humans has been an integral part of these factors.

This is a fairly intuitive reality for researchers, but also for the general public. On the other hand, it is an extremely delicate dynamic which depends on a bewildering number of factors which are themselves interdependent. It is therefore very difficult to extract statistical evidence from them.

The problem with this approach is that you have to be extremely rigorous in the selection of data. Otherwise, the slightest bias could completely skew all the results. To attempt to mathematically confirm this global dynamic, it is not enough to focus on a particular ecological niche; you have to find a candidate that is present all over the planet and has certain characteristics that are easy to compare.

A simple trefoil in the service of a massive study

To try to achieve this, researchers embarked on a massive study that mobilized 287 scientists from all over the world. “On the question of evolution, there has never been a field study on this scale.says Marc Johnson, an evolutionary biologist at the University of Toronto Mississauga.

Their choice fell on Trifolium repens, better known as creeping clover. This is a species that ticks all the boxes necessary for such work. Indeed, although it was initially documented in Europe and Central Asia, it gradually colonized the entire planet; it is now found in many cities around the world.

It is therefore a ideal subject to study the impact of Man. This army of researchers therefore collected more than 110,000 separate samples in different series. The former were collected directly in the middle of urban environments. The following groups, on the other hand, were collected further and further from the city, until the last ones that came from exclusively rural areas.

Human activity, represented by urbanization in the context of this study, represents a very significant selection pressure. © Piotr Chrobot – Unsplash

The researchers thus had a very large database at their disposal; they were thus able to extract statistically significant data, and therefore representative of the real impact of man on his direct environment.

They observed that on certain criteria, the clovers collected in urban areas were surprisingly similar between them. Even when they came from extremely distant cities geographically. Even more surprising: according to these same criteria, a city clover is generally closer to another city clover on the other side of the world than to a rural clover that has grown a few kilometers away, regardless of the climate!

In essence, this means that a Trifolium repens parisian would be genetically closer to a Marseille clover than to a clover collected in the countryside near the capital. This is very surprising, because genetic proximity generally depends very much on geographical proximity. But in this case, the genetically closest populations are geographically further apart, and vice versa.

And this is not a random finding, but a true statistical trend that can be demonstrated with mathematical tools. The inescapable conclusion therefore could not be clearer; human activity, symbolized here by urbanization, represents a very clear selection pressure that applies on a planetary scale.

The tip of a huge iceberg

To go into detail, this phenomenon observed by researchers is known asparallel evolution. This rather explicit term designates the comparable evolutions of different geographically separated populations under the effect of the same selection pressure – in this case, the way of life of mankind.

It is a phenomenon that can occur quite spontaneously in nature; the process is normal, and does not necessarily indicate an ecological disaster. But the extent, the speed and above all the cause of the phenomenon are particularly revealing in this precise case; because these little clovers are probably only the tip of the iceberg.

If they have undergone such marked changes, it is reasonable to expect that they are not the only ones; lots of other much more subtle and discreet changes, but just as substantial, probably occur in all the fauna and flora in more or less close contact with humans.

This work globally confirms the phenomenon that has already been observed on a smaller scale. Recently, we spoke to you, for example, of the consequences of human activity on birds, whose morphology evolves significantly with global warming.

This is the most compelling work to date to show how we alter the evolution of life”, explains biologist Rob Ness. “This knowledge can help us protect some of the world’s most vulnerable species […]and contribute to our fundamental understanding of the processes of evolution”, conclude the authors on a rather positive note which should not, however, overshadow the urgency of the situation.

The text of the study is available here.

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