BY: LAURA ROJAS
Evolution is something we’ve been graciously able to observe in countless species, allowing us to trace their origins back to when they were nearly unrecognizable. For some time, we’ve also been aware that humans can trigger ‘micro-evolutionary’ changes in different species. These changes are often exhibited as minor adjustments critical for survival, designed to help a species survive amongst our less-than-desirable human tendencies.
However, what we didn’t know is how rapidly these changes are actually starting to take place.
A process that commonly takes centuries, micro-evolutionary changes in species due to increased urbanization, is now happening within years.
Research conducted by Marina Alberti and published in Trends in Ecology & Evolution provides evidence of this rapid evolutionary process and its outcomes. An article by Emily Gertz from Take Part provides a few examples, stating: “pacific salmon in rivers are getting smaller, and some songbirds are changing their mating songs to find each other amid a city’s noise.”
Although these changes sound simple and minor, they actually have impending consequences for the ecosystems to which they belong. Gertz states that smaller salmon means their predators have to hunt more than normal, and new songbird calls could pose a struggle to reproduction when other birds can’t locate them because of their now different mating call.
Two evolutionary researchers from the University of Minnesota—Emilie C. Snell-Rood and Naomi Wick—discovered that not only are animals evolving in terms of behavior, but their brains are also getting physically bigger. Snell-Rood and Wick’s research involved gathering the skulls of mammals that lived in multiple rural and urban areas of Minnesota during the past 100 years and comparing the skull size of older specimens with the ones of the most recent. As suspected, the urban specimens had a larger skull size than their rural counterparts, and it is theorized that this is due to their need to adapt to city-life- increased brain size providing mammals with the tools necessary to adapt and cope with the multiple threats and stresses of the city.
However, the rural samples showed an increase in size as time went on, too. When looking back at how Minnesota’s rural geography evolved, it makes sense that clear cutting in order to make space for industrialized farms could have been a major factor at play. Their conclusion? “Our results provide some support of the hypothesis that urbanization selects for increased cognition, at least for a handful of species.”
The examples of urban evolution are exponential, but one of the most disturbing is the creation of ‘super spiders’. A study by Elizabeth Lowe written about in Citylab found that spiders living in the city “are bigger, pack on more body fat, and have heavier ovaries…suggesting they are great at having tons of spider babies.” Arachnophobics beware.
That isn’t really out of the blue either. The main factors contributing to insane spider growth include temperature and food supply. The heat of the city and the bright, fluorescent lighting that works great at attracting loads of insects make for the perfect spider growing conditions. This also means that other pests are ideal candidates for rapid evolution due to their tendency to thrive in urban areas.
Not so shockingly, this type of rapid evolution had not been observed before urbanization became such a widely recognizable phenomenon, leading experts to believe that these brisk, evolutionary changes—and the unknown consequences that surely follow—are no one’s fault but our own. These micro-evolutionary changes are certainly raising questions about sustainability, our human influence, and how to reduce our already alarming environmental impact.