Urban Darwinism

There tends to be a connotation with the word “evolution” that it’s a strictly natural process that only occurs in wild, rural environments. This is not the case; as our rapidly growing populations require the construction of more urban centers we inevitably build upon the niches of other species, yet many of them still avoid extinction. Natural selection can still occur in our cities over generations of species as new adaptations are being acquired within urban developments. Random genetic mutations may be deemed advantageous for survival in an isolated population of a species separate from its wild population, and if a trait becomes more common over generations the species becomes more genetically divers.

Evolutionary biologist Menno Schilthuizen has been studying the unprecedented influences humans put on the genes of plants and animals. He is focused on the fast-paced natural selection that species in cities and suburbs undergo to survive in ubiquitous human presence; he recently wrote a book about various urban evolutionary changes titled Darwin Comes to Town. Examples of these rapid changes within species are fascinating. Some populations of city birds have raised the pitch of their singing to a higher level than their wild cousins to adjust to traffic noise. Central Park white-footed mice have evolved two genes that allow for easier digestion of fatty foods littered by passing humans and for resistance against aflatoxin; these genes are not seen in other isolated city mice populations.

Caribbean crested anole lizards are undergoing physical changes to lamellae in their feet to better maneuver urban structures; skyscraper windows are much smoother than tree bark. An evolutionary genetics experiment was conducted that compared the ability of a forest crested anole and an urban crested anole to climb a concrete surface, and the forest crested anole was significantly worse at scaling the surface. City American cliff swallows wing’s are becoming shorter to more quickly vertically ascend to dodge oncoming traffic. Southern California bobcats are isolated into four sections by two major highways. Their isolation resulted in mange resistant genes. After an epidemic the surviving bobcats of one particular section were able to pass on their resistant genes; if interbreeding between populations had taken place the resistant genes may have been swamped from the other population’s genes. San Diego dark-eyed junco’s white tails and dark heads were changing in the city. In the forest the white tails and dark heads were of males that were more aggressive and successful in defending territory. However, in the city there's plenty of food, and less of a need for aggressive males to protect nests but more of a need for males to help raise their young. Consequently, the preference of urban females are changing. In the city white tails are disappearing and dark heads are becoming less striking.

 

These various isolated populations of different species were able to undergo random genetic changes to better suit the survival of future generations in the pressing presence of urban human activity and development. However, this does not mean that all species adapt because we don't observe the species that didn't. With very quick evolution comes many deaths within a species and so the takeaway is not that nature is completely fine in our rapidly urbanizing world, but rather it’s an observation on how evolution is affected. To preserve most of the earth’s biodiversity, untouched areas need to be protected for species that need untouched areas to not go extinct.

 

Posted by “Declan Downing” (1).