Darwin Comes to Town - A BOOK REVIEW
- Ayushi Mishra
- Jul 21, 2022
- 6 min read
Updated: Jan 1, 2023
How the urban jungle drives evolution?
Hands down, this has to be one of the best books I've ever read. As the name suggests, this book talks about how evolution happens in present times. It is a 2018 book and hence has neoteric insights on evolution. The author takes generous examples of species throughout the book and explains how they have evolved, as and when humans transform their natural habitats into cities/ urban settings.
Thoughts
Not a single point of condemnation built up in my brain while reading the book. It's short, it's crisp, it provides a great room for "learning" but nothing too crazy that I’ll forget. There are a lot of examples given in the book, but somehow I remember them all. It is not a super informative book that I’ll forget about. The language is simple with no load of jargons.
Background of the author:
The author, Menno Schilthuizen, is an evolutionary biologist / naturalist. He used to collect bug species in the Netherlands when he was young.
That being the case, he says that often naturalists are pre supposed to be working in forests or “natural settings” where many trees could be found, or mountains and deserts, places that have low human intervention. But why exclude cities where a major population resides and urbanization is at its peak. Urban naturalists in recent years have offered so much that it weighs heavy over some points put up by Darwin. Darwin’s evolution could take thousands to million years, but what is mind boggling is that contemporary evolution can take less than a century or even just a few decades.
A classic example of urban evolution is the 1st example that could come in someone's mind which we’ve probably heard in school. The “peppered moth” is a textbook example of urban evolution. These pale winged moths, during the industrial revolution were prone to predators(birds) as the tree trunks on which they lived turned black due to dust and soot(pollution). Hence the mutated black ones survived. Dark coloured moths outnumbered white ones within ~30 years. The Darwins's finches' have an urban dupe (Turdus merula ), which follow the same "beak story" but in a much faster pace and in cities.
The city's ecosystems are tremendously fragmented. Every garden, every lawn, every roof garden, every green belt between roads are potential habitats for animals. As cities were built, some species survived the change whereas others succumbed.
Every example mentioned is so interesting that I cannot stop listing. There are white footed mice of NYC, bobcats of Los Angeles and mosquitoes of the UK that are within the same cities but different gardens each exhibiting a unique species with some different gene pool. But the fragmented ecosystems pose big threats like inbreeding depression, species extinction etc.
We see house sparrows quite often in cities (more crows now). The house sparrow’s natural habitat is thickets of thorny trees and bushes. To them, the vast expanse of city perching-places like metal rods of varying thickness, density, inclination, and curvature perfectly resembles the brushwood of their original home. This is referred to as pre-adaptation. The sparrows were ready for human disruption.
Originally hailing from India and Africa, the bright green parakeet with its red beak and long tail has been hugely popular in the caged-bird trade for much of the twentieth century. The bird has effortlessly set itself up as an enterprising urban bird in northern Europe. The birds benefit from the urban heat islands and the fact that there is food to be had in cities in winter. It also helps that the species’ native range includes the foothills of the Himalayas, so it may already have been pre-adapted to cold spells.
So we can see that most of the animals which have evolved to these rapid changes have a predisposed advantage.
Apart from the rough and tough physical features of the cities, animals are also affected by noise pollution. Birds with low-pitched calls and songs, such as the mourning dove (Zenaida macroura), were absent from sites with compressors making loud noises. This is because birds can have a hard time communicating. Birds with high-pitched voices like the black-chinned hummingbird (Archilochus alexandri) actually preferred to build their nests near the compressors because their predators, Woodhouse’s scrub jays (Aphelacoma woodhouseii), cannot tolerate the noise. So for the hummingbirds, the noise actually affords protection.
Light pollution is also discussed and how some insects are negatively affected by them while others have adapted to this change.
After presenting uncountable fast-paced cases of evolution, the author questions - “But is it really evolution?” or could it be just adaptionation. The answer is simple. Fortunately, biologists have a very clear definition of what evolution is, “namely the change, over time, of the frequencies of gene variants”. If the physical differences arise as a result of change in the DNA sequence, then it is evolution, but if the change is not reflected in genes, then it is mere adaptation. Obviously, not all these observations can be taken to DNA sequencing and hence there are some generalizations. Like body(skin) color is mainly inherited but behaviors are often acquired(exceptions always exist).
But these are unfortunate incidents where animals fight hard to survive in cities. Many animals have tried to subdue humans. In 1975, the local carrion crows (Corvus corone) discovered how to use cars as nutcrackers. The crows have a predilection for the Japanese walnut (Juglans ailantifolia). The pretty nuts (a bit smaller than commercial walnuts, and with a handsome heart-shaped interior) are too tough for the crows to crack with their beaks, so for time immemorial they have been dropping them from the air onto rocks to open them. But this process is tedious. The crows would drop nuts among the wheels of slow-driving cars, and pick up the flesh after the car had passed. They would wait for the traffic light to turn red, then step in front of the cars, place their nuts, and hop back to the curb to wait for the lights to turn. When the traffic had passed, they would return onto the tarmac to retrieve their quarry. The birds would sometimes move a walnut a few centimeters if it took too long for it to be hit by a wheel. In one case, a crow would walk into the path of an oncoming car, forcing it to brake, and then quickly toss a nut in front of its wheels. Intelligent!
Tits (birds) in late nineteenth and early twentieth century in Europe used to steal cream (malai) from the milk cans delivered by milkmen. When this behavior was caught, milkmen started to cover the cans with cloth, but the birds managed to solve the conundrum. Then they switched to cloth, then to aluminum bottle caps, but the tits still managed to pierce through it.
After clearing the point on evolution vs adaptions, sexual selection is discussed. Sexual selection is the second most biggest rationale that drives evolution. The females select which male can do work like providing superior sperm, protection from predators, care for the young ones etc. Most appealing males are selected. Often male also get a chance to choose their companion. But urbanization has done worse to it. The Australian satin bowerbird, males of this species build amazing works of art to persuade females to mate with them. They create something akin to an ornamental garden, complete with passageways, entry lanes, and arrangements of beautifully shaped and colored objects that they harvest from their environment. They used rocks, shells, flowers, butterfly wings, and beetle elytra for this purpose. But, these days, humans supply an endless range of attractive artificial objects to add to his display like bright blue things—those rings that snap off the caps of milk bottles when you open them. Sadly, those rings turn out to be—an evolutionary trap. The ring flips backward and becomes trapped behind the nape of the neck. Thus permanently muzzled, the male then strangles himself or slowly starves. Our mindless interference with his pure aesthetic intentions brought on his downfall.
Similarly, Julodimorpha bakewelli (beetle) tries to copulate with a particular type of beer bottle. The animal mount the round bottom of the bottle and furiously but unsuccessfully try to penetrate the glass surface with its long, brown penis because the bottle resembles “shiny female backs”.
Our interference has taken out the best from evolution but has not given us the best overall. There are only a few species who manage to pull through, but a dozen perish.
We humans, as keystone species (a species with such a central role) must find ways to integrate as many species as possible in our urban settings. Like making roof gardens, vertical gardens etc. and not cementing our floors in place of lawn areas. The Dutch company Gewildgroei (an untranslatable pun meaning, Desirable Growth) designs and distributes pavement tiles that contain gaps and holes for soil to collect and plants to sprout spontaneously.
The book ends with a note from the author giving an account of his experience when he visits his hometown after 40 years.
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