Urban evolution can have different meanings depending on what field you come from. If you are an urban planner, it might mean that urban areas are getting larger, even using sustainable energy sources where they didn’t previously. For some architects it may mean that they now figure out how to put green roofs on buildings. Evolutionary biologists see urban evolution simply as evolution that happens in/ because of urban areas.
Let’s break that evolutionary biology definition a bit. Evolution is defined as a change in allele frequencies in a population. This can happen because of four different processes: mutation, gene flow, genetic drift, or selection.
Mutation:
Mutations happen naturally in genomes, we have even measured out mutation rates for many different kinds of organisms. In urban areas, mutations can occur faster than the base mutation rate because of things like pollution.
Gene Flow:
Gene flow is the movement of alleles between populations. Changes to gene flow occur naturally, sometimes over long periods of time, like glaciation events, and sometimes over shorter periods of time. Because urbanization changes the natural landscape, it can impede gene flow by creating barriers, like roads. Sometimes urbanization can increase gene flow for some organisms because humans accidentally bring them along for the ride between urban areas. I recently gave a talk at the Evolution conference on this topic.
Genetic Drift:
Genetic drift causes random fluctuations to alleles in populations. By chance, some alleles will stay in a population, not because they are better. The strength of genetic drift is inversely related to the total population size, so that smaller populations are more susceptible to genetic drift. So in urban areas, we see patches of habitat, like parks, that have populations that are much smaller than their natural populations. These park populations are then more strongly influenced by genetic drift.
Selection:
Finally, there is natural selection. This is where alleles are lost because they are “bad” or alleles increase in frequency because they are “good”. For organisms that do well in the urban environment, it is likely that they adapted to this new urban habitat. My fellow editor has done some great research in this area, check out her most recent post: Do Anoles Adapt to Urbanization in Similar Ways?
I am interested in urban ecology and evolution. Urbanization can have drastic impacts on local ecosystems, both negative and positive, and creates a new environment for organisms to experience. To understand the impacts that urbanization plays on organisms, I look through the lense of population genetics and molecular evolution.
- Urban Observation of the Week: Golden Jackal - July 28, 2021
- Urban Observation of the Week: Bellflowers in Munich - July 21, 2021
- Urban Observation of the Week: So Many Plants - July 14, 2021
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