War, politics, religion shape wildlife evolution in cities

Elizabeth Carlen for The Conversation

Missouri: People often consider evolution to be a process that occurs in nature in the background of human society.

But evolution is not separate from human beings. In fact, human cultural practices can influence evolution in wildlife. This influence is highly pronounced in cities, where people drastically alter landscapes to meet their own needs.

Human actions can affect wildlife evolution in a number of ways. If people fragment habitat, separated wildlife populations can evolve to be more and more different from each other.

If people change certain local conditions, it can pressure organisms in new ways that mean different genes are favoured by natural selection and passed on to offspring – another form of evolution that can be driven by what people do.

In a recent review, evolutionary biologists Marta Szulkin, Colin Garroway and I, in collaboration with scientists spread across five continents, explored how cultural processes – including religion, politics and war – shape urban evolution.

We reviewed dozens of empirical studies about urban wildlife around the globe. Our work highlights which human cultural practices have and continue to shape the evolutionary trajectory of wild animals and plants.

Religious practices

If you’ve travelled internationally, you may have noticed the menu at any one McDonald’s restaurant is shaped by the local culture of its location.

In the United Arab Emirates, McDonald’s serves an entirely halal menu. Vegetarian items are common and no beef is served in Indian McDonald’s.

And in the United States, McDonald’s Filet-O-Fish is especially popular during Lent when observant Catholics don’t consume meat on Fridays.

Similarly, ecosystems of cities are shaped by local cultural practices. Because all wildlife are connected to the environment, cultural practices that alter the landscape shape the evolution of urban organisms.

For example, in Oviedo, Spain, people constructed walls around religious buildings between the 12th and 16th centuries. This division of the city led to different populations of fire salamanders inside and outside the walls.

Because salamanders can’t scale these walls, those on opposite sides became isolated from each other and unable to pass genes back and forth.

In a process that scientists call genetic drift, over time salamanders on the two sides became genetically distinct − evidence of the two populations evolving independently.

Imagine dumping out a handful of M&Ms. Just by chance, some colours might be overrepresented and others might be missing.

In the same way, genes that are overrepresented on one side of the wall can be in low numbers or missing on the other side. That’s genetic drift.

Introducing non-native wildlife is another way people can alter urban ecosystems and evolutionary processes.

For example, prayer animal release is a practice that started in the fifth or sixth century in some sects of Buddhism.

Practitioners who strive to cause no harm to any living creature release captive animals, which benefits the animal and is meant to improve the karma of the person who released it.

However, these animals are often captured from the wild or come from the pet trade, thereby introducing non-native wildlife into the urban ecosystem. Non-natives may compete with local species and contribute to the local extinction of native wildlife.

Capturing animals nearby has downsides, too. It can diminish local populations, since many die travelling to the release ceremony. The genetic diversity of these local populations in turn decreases, reducing the population’s ability to survive.

Influence of politics

Politically motivated campaigns have shaped wildlife in various ways.

Starting in 1958, for instance, the Chinese Communist Party led a movement to eliminate four species that were considered pests: rats, flies, mosquitoes and sparrows.

While the first three are commonly considered pests around the world, sparrows made the list because they were “public animals of capitalism” due to their fondness for grain.

The extermination campaign ended up decimating the sparrow population and damaging the entire ecosystem. With sparrows no longer hunting and eating insects, crop pests such as locusts thrived, leading to crop destruction and famine.

In the United States, racial politics may be shaping evolutionary processes in wildlife. For instance, American highways traverse cities according to political agendas and have often dismantled poor neighbourhoods of colour to make way for multi-lane thoroughfares.

These highways can change how animals are able to disperse and commingle. For example, they prevent bobcats and coyotes from travelling throughout Los Angeles, leading to similar patterns of population differentiation as seen in fire salamanders in Spain.

Wildlife during and after war Human religious and political agendas often lead to armed conflict. Wars are known to dramatically alter the environment, as seen in current conflicts in Gaza and Ukraine.

While documenting evolutionary changes to urban wildlife is secondary to keeping people safe during wartime, a handful of studies on wildlife have come out of active war zones. For example, the current Russia-Ukraine war affected the migration of greater spotted eagles.

They made large diversions around the active war zone, arriving later than usual at their breeding grounds. The longer route increased the energy the eagles used during migration and likely influenced their fitness during breeding.

Wars limit access to resources for people living in active war zones. The lack of energy to heat homes in Ukraine during the winter has led urban residents to harvest wood from nearby forests.

This harvesting will have long-term consequences on forest dynamics, likely altering future evolutionary potential.

A similar example is famine that occurred during the Democratic Republic of Congo’s civil wars (1996-1997, 1998-2003) and led to an increase in bushmeat consumption.

This wildlife hunting is known to reduce primate population sizes, making them more susceptible to local extinction.

Even after war, landscapes experience consequences.

For example, the demilitarized zone between North Korea and South Korea is a 250 km barrier, established in 1953, separating the two countries.

Heavily fortified with razor wire and landmines, the demilitarised zone has become a de facto nature sanctuary supporting thousands of species, including dozens of endangered species.

The collapse of the Soviet Union and the end of the Cold War led to the establishment of the European Green Belt, which runs along the same path as the Iron Curtain.

This protected ecological network is over 12,500 km long, allowing wildlife to move freely across 24 countries in Europe. Like the Korean DMZ, the European Green Belt allows for wildlife to move, breed and exchange genes, despite political boundaries.

Politics has removed human influence from these spaces, allowing them to be a safe haven for wildlife.

While researchers have documented a number of examples of wildlife evolving in response to human history and cultural practices, there’s plenty more to uncover.

Cultures differ around the world, meaning each city has its own set of variables that shape the evolutionary processes of wildlife.

Understanding how these human cultural practices shape evolutionary patterns will allow people to better design cities that support both humans and the wildlife that call these places home.

(Elizabeth Carlen is a Living Earth Collaborative Postdoctoral Fellow, at Washington University in St. Louis)