Against the Grain: How Human Landscapes Are Fueling New Evolution
- Ash
- May 30
- 9 min read
Updated: Jul 24
Table of Contents
Introduction – A More Complicated Story
Anthropogenic Pressure as Evolutionary Force
Urban and Suburban Evolution
Novel Ecosystems as Evolutionary Arenas
Linear Corridors: Railways, Roadsides and Canals
Garden and Agricultural Edge Evolution
New Hybrids, New Lineages
Soil, Microbes, and Invisible Evolutions
Conclusion – Evolution Within Human Landscapes
Glossary
References
Introduction – A More Complicated Story
For much of recent history, the story of humanity’s impact on the natural world has been one of decline and extinction. From the loss of forests and wetlands to the spread of pollutants and the disappearance of iconic species, there is no denying the damage done. Yet this focus on loss can sometimes obscure a more nuanced truth. Where landscapes have been changed—sometimes dramatically—by human hands, evolution itself has not stopped. In fact, new forms of life and new adaptations are emerging at surprising speed, particularly among plants, invertebrates, and the hidden world of soil microbes. While this does not cancel out the costs of extinction, it reminds us that life’s creativity and resilience are still at work, even in the most unexpected settings.
This article explores how human activity, from urban development to gardening and farming, is creating novel evolutionary arenas. Across the UK and Europe, and in similar places worldwide, we find examples of species rapidly adapting to new challenges, forming new hybrids, and carving out fresh ecological niches. This is not an argument for complacency, but an invitation to observe and understand the evolutionary story still unfolding around us.
Anthropogenic Pressure as Evolutionary Force
When biologists talk about natural selection, they often picture wild landscapes—mountain meadows, rainforests, or untouched heath. Yet for a growing number of species, the most powerful selective forces now come from people and the environments we create.
Urban Selection Pressures
Urban areas present a unique suite of selection pressures. High temperatures, patchy water availability, artificial light at night, noise pollution, heavy metal contamination, and frequent physical disturbance all shape which species survive and thrive. Plants and animals alike must navigate fragmented habitats, unpredictable resources, and new threats or opportunities.
For example, the heat-island effect in cities favours plants that flower earlier, tolerate drought, or possess reflective leaf coatings. Urban blackbirds have evolved higher-pitched songs to be heard above traffic. Moths in lit environments show reduced attraction to streetlights. Some snails now sport darker shells in response to city microclimates, while certain isopods (woodlice) in urban parks display greater tolerance for desiccation.
Novel Ecological Niches
Human-modified spaces also generate entirely new niches. Garden beds, canal banks, compost heaps, and roadside verges offer a patchwork of resources not found in pre-human environments. Many of these habitats are less stable or predictable than wild systems, encouraging a suite of traits—rapid growth, high dispersal, tolerance for disturbance—that favour species capable of swift adaptation.
Climate-Forced Range Shifts
The combination of changing climate and altered landscapes is forcing many species to move. Plants and invertebrates are shifting northward or to higher elevations, often using roadsides, railway verges, or canal banks as stepping stones. Along these corridors, evolutionary changes can be observed in real time. For instance, salt-tolerant Plantago populations have emerged independently on motorway edges across several countries—a powerful example of parallel evolution under anthropogenic conditions.
Urban and Suburban Evolution
Some of the most compelling evidence for rapid evolution comes from ordinary city streets and suburban gardens. Here, populations of common species are diverging from their rural relatives, sometimes within a few decades.
City–Rural Adaptation Gradients
One classic example is the white clover (Trifolium repens) and its production of hydrogen cyanide, a chemical defence against herbivores. In urban centres across Europe, clover populations tend to lose this trait, likely because the cost of producing cyanide outweighs the benefit when grazers are scarce. The result is a sharp gradient in clover chemistry from the city centre to the rural fringe, with evolution clearly tracking the urban landscape.
Rapid Weed Chemistry Shifts
Other weeds also display quick adaptation. Heavy metal-tolerant grasses have evolved on old industrial land and urban lawns, while annual plants such as Oxford ragwort (Senecio squalidus) have rapidly adapted their flowering times and growth forms to suit city railways and disturbed sites.
Animal and Invertebrate Urban Traits
Urban birds, such as blackbirds and great tits, not only alter their songs but also their behaviour, nesting earlier and showing increased boldness around people. Invertebrates, including butterflies and moths, are adapting their activity patterns to artificial light regimes. Soil invertebrates, such as springtails and mites, are evolving tolerance to high levels of urban pollutants and fluctuating moisture.
Novel Ecosystems as Evolutionary Arenas
While the concept of “novel ecosystems” often focuses on changes in species composition, these settings are increasingly recognised as laboratories of evolution.
Spontaneous Hybrid Zones
Post-industrial brownfields, abandoned rail yards, and even urban parks frequently harbour hybrid swarms—populations where related species mix and, over time, stabilise new genetic combinations. The London plane tree (Platanus × acerifolia), which originated from a hybrid between two continental species, is now widespread across European cities, its hybrids thriving in urban soils.
New Plant–Pollinator Dynamics
Novel plant communities can attract both native and introduced pollinators, leading to unexpected new relationships. Some solitary bees have adapted to forage on garden exotics, while hoverflies and bumblebees exploit longer flowering seasons in mixed-origin food forests and canal margins. Parasite and pathogen dynamics shift as well, with new hosts and transmission routes appearing in urbanised communities.
Food Forests as Testbeds
Food forests—designed multi-layered plantings of both native and exotic species—represent deliberate experiments in ecological assembly. Long-term monitoring shows not only high productivity and resilience to pests, but also the emergence of new plant-insect and soil mutualisms. Some garden-origin plant species, once introduced, have naturalised and even adapted further to local soils and climates, sometimes developing novel traits or associations with native fungi and bacteria.
Linear Corridors: Railways, Roadsides and Canals
Infrastructure corridors, often overlooked, are powerful drivers of evolutionary change.
Seed Dispersal and Adaptation
Railway lines, canal banks, and motorway verges offer linear habitats that connect otherwise isolated populations. They facilitate gene flow and dispersal, but also select for specific traits—drought tolerance, salt resistance, rapid seed maturation. Many classic “railway plants”, such as Oxford ragwort, spread rapidly along tracks, evolving forms and phenology distinct from their Italian ancestors.
Drought, Salt, and Metal Tolerance
Metal-resistant ecotypes of grasses and wildflowers can be found along the edges of busy roads and former industrial tracks. Salt from winter gritting favours halophytes, such as Plantago and sea lavender, now thriving far from their coastal origins. Drought-adapted forms of yarrow and dandelion are increasingly common on compacted urban verges.
Parallel Evolution Across Verges
The repeatability of these evolutionary responses is striking. Salt-tolerant traits, for instance, have evolved in parallel across motorway verges from France to Scandinavia, while metal tolerance in Silene vulgaris and Festuca rubra appears in multiple cities and countries, often within a few decades.
Garden and Agricultural Edge Evolution
Human-managed landscapes are also sites of rapid and ongoing evolution.
Weed Radiation and Crop Mimicry
Weeds often evolve to resemble the crops they infest—a classic example is rye (Secale cereale), which became a crop itself after evolving to mimic wheat in European fields. In urban gardens and allotments, ruderal species such as borage and fat hen (Chenopodium album) display high genetic turnover, adapting to annual cycles of disturbance, compost addition, and selective weeding.
Invertebrate Host-Switching
Garden plants can provide new hosts for invertebrates, with some insects switching from native to exotic species. Aphids, leaf miners, and beetles are increasingly observed on imported ornamentals, sometimes showing rapid adaptation in feeding behaviour or life cycle timing. In compost heaps, earthworms and detritivores adapt to altered temperatures and nutrient profiles, leading to shifts in community structure.
Allotments and Compost Mutation Sinks
Allotments and compost piles act as “mutation sinkholes”—places with high rates of disturbance, introduction, and turnover. Here, both plants and invertebrates experience strong selection and frequent novel mutations. Over time, some lineages stabilise new traits, such as disease resistance, drought tolerance, or altered growth habits.
New Hybrids, New Lineages
Human-modified environments often favour hybridisation, occasionally resulting in the emergence of new lineages.
Hybridisation Stabilised in Novel Habitats
The most famous British example is Spartina anglica, a saltmarsh grass formed by hybridisation between a native and an introduced species on the south coast. It quickly became a dominant plant in estuaries, with unique genetics and traits. The London plane is another, thriving as a stable hybrid in urban parks and streets.
Animal examples exist as well. Urban gull populations in some European cities show admixture between herring and lesser black-backed gulls, leading to new forms with distinct behaviour and nesting habits. In city parks, Columba pigeon populations show hybridisation and divergence from their rural counterparts.
Incipient Speciation Evidence
While most urban hybrids remain part of broader gene pools, there is growing genomic evidence for partial reproductive isolation in some lineages. Key thresholds, such as one percent genome divergence or stable hybrid zones, have been documented in grasses, trees, and certain soil invertebrates.
Fresh Examples
Hybrid broomrapes (Orobanche species) are emerging in disturbed soils, some forming host-specific races on exotic plants within a few decades. These cases show the potential for human-modified environments to drive incipient speciation, not just in plants but also in fungi and soil fauna.
Soil, Microbes, and Invisible Evolutions
Much of the evolutionary action in novel landscapes occurs out of sight, among soil microbes and their plant partners.
Horizontal Gene Transfer and Nutrient Cycles
Urban and brownfield soils support microbial communities with high rates of horizontal gene transfer, facilitating rapid adaptation to pollutants, novel organic matter, and fluctuating moisture. Some bacteria have developed new pathways for nitrogen cycling or contaminant breakdown within just a few years of soil formation.
Root-Zone Co-Evolution
Plants and their rhizosphere microbes are co-evolving in novel settings. Mycorrhizal fungi associate with both native and exotic hosts, while plant exudates influence which bacteria and fungi thrive. Over time, these relationships can lead to unique microbial communities that enhance plant growth or resilience.
Timescales of Microbial Adaptation
Recent studies show that microbial community turnover in new soils can happen in as little as five to ten years, with adaptive traits emerging rapidly under strong selection. This hidden layer of evolution underpins many visible changes in plant growth and health in novel habitats.
Conclusion – Evolution Within Human Landscapes
It is tempting to view humans as simply a destructive force in nature, but the reality is more complex. Our cities, farms, roads, and gardens are not only sources of extinction but also landscapes where evolution continues to play out in real time. Across the UK, Europe, and the wider world, species are adapting, diversifying, and sometimes forming new lineages in response to our presence.
Understanding these processes does not diminish the need to conserve what is left of wild nature. Rather, it highlights the power of life to find opportunities even amid disturbance and change. As citizen scientists, naturalists, or simply observers, we have a unique chance to witness evolution as it happens—sometimes quite literally in our own back gardens.
Glossary
Adaptive radiation: The rapid diversification of a lineage into new forms and species, typically in response to novel ecological opportunities.
Allotment: A small plot of land, often urban, rented for growing vegetables or flowers.
Anthropocene refugia: Human-modified habitats that serve as safe havens for some species or genetic lineages.
Anthropogenic selection: Evolutionary change driven by human activities and altered environments.
Commensal species: Organisms that live in close association with humans or human infrastructure, often benefiting from the relationship.
Cryptic speciation: The evolution of new species that are difficult to distinguish by appearance but are genetically distinct.
Genomic cline: A gradual change in genetic composition across a geographic gradient.
Hybrid swarm: A population composed of hybrids and backcrosses, often found where two or more species interbreed.
Functional redundancy: The presence of multiple species that perform similar roles in an ecosystem, providing resilience against change.
Local adaptation: The process by which populations evolve traits that enhance survival and reproduction in their specific environment.
Mutation sinkhole: A habitat or site with high rates of mutation, introduction, and genetic turnover, often due to disturbance or management.
Urban gradient: The change in environmental conditions and species traits observed from the centre of a city out to rural surroundings.
References (selected):
Thompson et al. (2022), Journal of Urban Ecology – Rapid adaptation in urban clover populations
Blanusa et al. (2019), Journal of Applied Ecology – Pollinator use in novel plant communities
Schroeder et al. (2021), Science of the Total Environment – Soil microbial adaptation to urban pollutants
Pearman & Preston (2018), BSBI News – Railway flora evolution in the UK
Vincent et al. (2020), Nature Communications – Hybridisation and divergence in urban gulls
DEFRA (2022), Soil health and urban land-use audit
Urban Food Forests Network (2021), European project directory
Angold et al. (2006), Urban Ecology – Brownfield biodiversity and adaptive plant traits
van der Veken et al. (2008), Global Change Biology – Range shifts and adaptation in European flora
London Natural History Society (2020), Flora of London brownfields
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