City animals are changing their physical characteristics

Evolutionary biologist Rob Dunn, in his 2022 book A Natural History of the Future maintains that evolution can occur quicker than people think – mostly unnoticed, right under our noses. Evolution is happening when the physical characteristics of animals change over time, or new types of animals develop, or some animal species disappear.

Rob Dunn first explains how animal species can evolve and change. One way is through isolation – when animals are separated from other species, they can diverge and change some of their physical characteristics. Another way is through a change of diet, and another way is through geographical barriers.

He gives examples of city animals changing their physical characteristics. For example, New York rats have longer noses and smaller upper molar tooth rows than rats from the 1890s. It might be due to a change of diet, such as access to more nutritional food. Scientists at Fordham University in New York showed that there was a difference in their 2017 genetic analysis of brown rats in New York. The scientists also found that uptown rats from Manhattan avoided mating with downtown rats. It may be because there is a geographical barrier between the two areas – in the middle is a commercial district with minimal household trash. Rats live on trash and so they did not go through the commercial district because there was less food to eat there.

Rob Dunn gives an example of a pigeon study by Washington University in St. Louis, Missouri, America. Scientists studied pigeons in different American cities. The lice that lives on the bodies of pigeons is changing its physical characteristics faster than previously because its life span is shorter than before. The scientists think that species with shorter generation times evolve at a faster pace than others.

Studies at Rutgers University in New Jersey, America, across many large cities around the world, showed that the Common House Mosquito (Culex pipiens) is changing its physical characteristics. Specifically, below-ground mosquitoes in underground stations are becoming different from above-ground mosquitoes. Scientists have called the underground mosquitoes Culex pipiens f. molestus. Above-ground mosquitoes are seasonal, active in the warmer months, the females prefer to suck blood from birds, and require a meal of blood before they can lay eggs. Underground (subterranean) mosquitoes are active all year round, and the females feed on mammal blood and can lay eggs without needing to feed on blood first. But even the London Victorial Line station mosquito is genetically different from the Bakerloo Line station mosquito, which might be due to the different food sources in the sewers. 

A 2020 study at the University of Glasgow in Scotland looked at city foxes in comparison with rural foxes. The scientists found that city foxes have shorter, wider snouts (noses) that rural foxes. 

City animals seem to be affected by the changing food that is available, which changes as people’s food habits change. For example, in some parts of cities, humans might eat more carbohydrates than people in other parts of cities, or more protein, etc. Animals are also learning how to get food out of trash cans and bins – particularly birds, rats, and insects.

Conditions are variable in different cities and also in different parts of the same city. Scientists, called evolutionary biologists, continue to study and observe animals to see if they are changing their physical characteristics over time. 

Why is this important? Studying changes in the physical appearance of animals helps humans to know what processes are influencing the changes – why they are changing. It helps to solve biological problems that impact our lives – we might be able to learn from the information to control hereditary disease in people, and how to improve the quality of human life. The information is also important for the conservation of animals and their environment. 

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