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Cats, dogs and farm animals are what come to mind when we think of domesticated animals. For ages, domestication has been portrayed as a uniquely human accomplishment, where species become domestic only through our deliberate control.

This belief is supported by the fact that human interference has not only reshaped the planet, but also significantly altered plants and animals; agriculture and rangelands now occupy about one-third of Earth's land surface. Humans, along with our pets and livestock, account for more than 90% of the global mammalian biomass.

While the idea that domestication is controlled by humans is not entirely false, it still fails to capture the full complexity of how the domestication process truly unfolds.

So what exactly is domestication? It is a question scientists have revisited time and again—yet there is no reliable, universally accepted and consistent definition for it.

To answer this query and rectify preconceived notions, a collaborative team of researchers from the U.S. and the U.K. proposed a universally relevant definition for domestication. According to their recent study in the Proceedings of the National Academy of Sciences, domestication should be viewed as an evolutionary process resulting from the interaction between two species, one of which is human, and the other a species that cannot sustain itself outside the environment created by human activities or an anthropogenic niche.

This perspective presents domestication as a form of evolution that, like any other, acts on individual populations. It challenges the longstanding false dichotomy that separates domestication, often viewed as the result of artificial selection, from the natural selection that drives evolutionary changes elsewhere in the natural world.

Previous attempts to define domestic organisms have heavily leaned on the construct of human control, intentionality and exceptionalism—a belief that humans are superior to other animals. They characterized domestic populations as those whose nutrition, safety and breeding are managed by humans.

Contrary to the popular notion, most populations that are typically considered domestic are not actually under direct human control. For instance, 76%–83% of dogs live beyond direct human control, and even the beloved blackberry can also act as a weed and spread into unwanted areas, causing damage.

After a thorough literature review of this field, the team identified the fundamental issues and inconsistencies in numerous previous attempts to define domestication. Drawing on the knowledge and its gaps, the researcher provided a new definition: Domestication should be understood solely as the evolution of a nonhuman population in response to a human-shaped environment. In addition, a population's domestication status should be judged only by its relationship with this anthropogenic niche and not by comparisons to some unseen or hypothetical ancestor.

The five main categories in the spectrum include: obligate recluses, which thrive in the absence of human disturbance; human avoiders, which exist where human disturbance is rare; human-tolerant species, which live in areas with occasional human presence; human exploiters, described as opportunists; and finally, obligate synanthropes or domestic populations, which require ongoing human activity to survive.

The researchers believe that this definition will allow us to understand why some species survive and thrive, while others struggle and go extinct in response to the conditions human societies create. In a world where human impact is rapidly transforming ecosystems, understanding domestication is more important than ever for preserving biodiversity.

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