Among all the benefits of living in a small town, the one that means most to me is living close to nature. As an avid birdwatcher, I have spent many summer mornings along with my sister wandering around in the mountains with a pair of binoculars and gazing up at birds in the trees. Since I have a keen eye out for local birds and animals, I recently noticed that the number of pigeons is increasing rapidly where I live, as human civilization and population has developed increasingly in my town since I was a kid. I almost cannot imagine pigeons living in the wild anymore. As we trained them and domesticated them as far as 10,000 years ago, cities became the perfect backdrop for the pioneering success of the species. Pigeons have not only adapted to reside near apartment buildings and live on scraps, they have also evolved ways to detox themselves from heavy pollution in cities. We often tend to view evolution as an imperceptible, achingly slow process spanning over hundreds, even thousands of years. We think of it as something that happened in the past, something that we cannot observe now.
We see nothing of these slow changes in progress until the hand of time has marked the lapse of ages. -Charles Darwin
Or do we?
How Animals Evolved to Live Alongside Humans?
Due to fast-changing environmental conditions like climate change, human encroachment, pollution, urbanization, and habitat fragmentation, evolutionary biologists have come to realize that sometimes evolution can happen at a much faster rate and in fact, can be observed. This kind of high-speed adaption is termed as Evolutionary Rescue or Urban Evolution.
When the environment that animals live in, changes drastically, most species who are not able to cope with it, sadly go extinct. But the ones that don't, adapt and evolve in spectacular ways. It is incredible to see how animals evolve under such conditions.
Evolutionary biologist Menno Schilthuizen, author of Darwin Comes To Town says,
Urban environments are powerhouses of evolution where diverse animals adapt to new surroundings with startling results.
We are all surrounded by urban wildlife like insects, rats, pigeons, sparrows, raccoons, squirrels, and monkeys which are synanthropic, ecologically associated with, and even evolved to become largely dependent on human beings. As their habitats begin to disappear, animals have to do what they can, to survive. For example, mice that live in cities have evolved to digest very fatty human food. The European garden snails have developed shells that are lighter in color to help them stay cool in the city heat. Grasshoppers have adapted higher frequencies of sound for living near traffic.
The evolution of the London Underground mosquitoes is an especially popular instance of high-speed adaptation. This is one of the cases where an entirely new species of mosquitoes evolved to meet the changes in the environment.
During the London Underground systems' construction in 1863, a novel habitat for the mosquito subspecies of Culex pipiens was created there. Stagnant water collected in the tunnels made a perfect breeding ground for the bloodsuckers. After the construction was done, the tunnels were almost sealed off and the mosquitoes were trapped underground.
The mosquitoes, which above ground usually feed on birds, had to switch to drinking the blood of mammals like rats which were more common there. This whole process took place in just around 8 decades. Humans have discovered this during the Second World War when the tunnels were used as overnight bomb shelters and were ravaged by mosquitoes. The original mosquito species and the new underground species turned out to be so distinct that they couldn't mate anymore and produce offspring. So the underground mosquito is arguably a new species and not a subspecies that evolved through the span of only a few hundred mosquito species.
What is it called? And How it happened?
Industrial melanism is a way in which animals evolve to have darker-colored skin or feathers to protect themselves from industrial pollution. An Australian species called the turtle-headed sea snake generally had black and white stripes. But around 17 years ago, researchers observed that the turtle-headed sea snakes living in Noumea Lagoon in New Caladonea were losing their stripes and mostly black instead. They get that color from a pigment called melatonin. This pigment is also very good at binding to heavy metals like zinc, lead, and arsenic. These metals are generally toxic to animals and cause them to die.
The waters in New Caladonea are full of heavy metals due to nearby nickel mining and industrial runoff. The dark skins of these snakes were found to have higher concentrations of trace elements such as arsenic and zinc than the snakes far from cities. By shedding their skin very frequently they can rid their skin of toxic substances.
Another instance of melanism in evolution is that of the peppered moths. In England, these moths that were sandy brown colored, blended nicely on the tree barks, to escape predators. But in the 1950s, coal smoke had darkened the trees and the pepper moths were out of places to hide in, that is until a darker form of these pepper moths evolved to blend on the tree barks.
There are countless more instances where animals underwent drastic changes to adapt themselves to the new environment. Cliff swallows build their nests on bridge supports. This means they are dangerously close to traffic. But eventually, the swallows' wings became shorter in length, making them more maneuverable, agile, and fast to escape oncoming cars, all within three decades.
Sport fishes like salmon, cod, and herring have grown smaller in size to escape fishing nets and grow sexual maturity faster, to reproduce quicker.
Another such example is of the African elephants that are the victims of poaching for their tusks. This gave an advantage to the female elephants that were generally tuskless. Lacking tusks went from an uncommon trait to being a widely common one possessed by up to a third of female elephants. This has all happened for only a couple of generations.
Here we have seen how animals have evolved over the years and very quickly in the recent years. Evolution is an ongoing process that has been happening. But Human intervention in the nature is making it happen at a rapid pace and mostly creating problems to us. So, it is something like Karma coming back.
Author - Ketaki Watve
Books we recommend you to refer are
Fact File:
New Scientist - Sea Snakes turning Black
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