Domestication is the multi-generational process of humans adapting wild plants and animals for their use, which has reshaped the planet’s biology by changing the geographical area where these species are found. For thousands of years, humans have selectively bred plants and animals, influencing their evolution to better provide resources like food and labor. The result is a global map of life dramatically different from what existed before human intervention.
From Localized Origins to Global Presence
Every domesticated species has a “center of origin,” a geographic area where its wild ancestors first lived and were brought under human management. Over millennia, human activities have expanded these localized ranges, transforming select organisms into a global presence on every continent except Antarctica.
Many important food crops originated in specific locales. Wheat and barley, for example, were first cultivated in the Fertile Crescent of the Middle East around 11,000 years ago. From this cradle of agriculture, they spread to become staple foods grown across the globe. Maize, known as corn, traces its ancestry to a wild grass called teosinte in Mesoamerica and is now a dominant global commodity grown far from its origins.
Modern cattle are descended from the aurochs, a large wild bovine that once roamed across Eurasia and North Africa. After their domestication in the Near East roughly 10,000 years ago, cattle were transported by migrating human populations across the world. Chickens trace their lineage to the red junglefowl of Southeast Asia. Now, they are the most numerous bird on the planet, raised for meat and eggs in virtually every country.
Mechanisms of Human-Driven Expansion
The global spread of domesticated organisms was driven by distinct human activities. Early farmers were the first vectors of this expansion, carrying the seeds of their crops and the young of their livestock as they migrated into new territories. This movement established domesticated species across continents, a process that accelerated as human populations grew. The spread of agriculture from the Fertile Crescent into Europe, North Africa, and parts of Asia was facilitated by these migrating communities.
Later, trade and exploration dramatically increased the speed and scale of this dispersal. The Columbian Exchange, initiated by voyages across the Atlantic in the late 15th century, was a significant moment in this biological globalization. European explorers introduced Old World species like horses, pigs, and wheat to the Americas. In return, New World species such as potatoes, tomatoes, and maize were transported back to Europe, Africa, and Asia, where they revolutionized diets and agricultural practices.
Industrial agriculture and modern transportation have pushed this expansion to an unprecedented level. Globalized supply chains, refrigerated shipping containers, and large-scale commercial farming have made it possible to produce and distribute agricultural products almost anywhere. This system relies on a few highly productive breeds and crop varieties, further homogenizing the distribution of these species. The efficiency of modern logistics ensures that a handful of domesticated organisms now dominate global food production.
Transformation of Habitats and Niches
The spread of domesticated species required altering environments to support them. Humans have actively reshaped natural landscapes to create artificial habitats tailored to the needs of their crops and livestock.
Vast areas of the planet’s forests, grasslands, and wetlands have been repurposed for farming. Native prairies and savannas were converted into pastures for grazing cattle, sheep, and goats. These agricultural landscapes are human-made ecosystems, maintained through plowing, irrigation, and fertilization. They support only the selected domesticated species and a few other organisms adapted to these modified conditions.
Beyond rural landscapes, human settlements have become novel environments for certain species. Cities and suburbs create a unique “urban niche” that a select group of organisms has successfully exploited. Species like the rock pigeon, house mouse, and brown rat have distributions now almost entirely linked to human settlements. These animals thrive in the artificial structures and abundant food waste that cities provide, a cohabitation dependent on human-altered environments.
Consequences for Wild Counterparts
The global expansion of domesticated species has had detrimental effects on their wild relatives. As human agriculture spread, the habitats of wild ancestors and other closely related species were destroyed or fragmented. This process has led to declines in the populations and geographic ranges of many wild counterparts, pushing some toward extinction.
A direct consequence is range contraction. The clearing of land for farms and pastures eliminated the natural ecosystems that wild species depended on. The wild aurochs, the ancestor of modern cattle, was driven to extinction in the 17th century due to habitat loss and hunting. Similarly, the wild junglefowl, ancestor of domestic chickens, faces threats from habitat destruction in its native Southeast Asian forests.
Another impact is genetic interbreeding between domesticated organisms and their wild cousins. When domesticated animals escape or are released into the wild, they can breed with native populations, a process sometimes called genetic pollution. This dilutes the unique genetic adaptations of wild populations. For example, interbreeding between escaped farmed salmon and wild salmon populations threatens the genetic integrity of the wild fish. Likewise, the hybridization of domestic dogs with wild wolves and coyotes can alter the genetics and behavior of these native predators.
Establishment of Feral Populations
When domesticated animals escape or are abandoned and form self-sustaining populations, they are known as feral. This phenomenon occurs when human-transported species establish themselves in foreign ecosystems without direct human control. These feral animals can become invasive species with profound impacts on their new environments.
Feral populations can cause ecological disruption by outcompeting native wildlife, preying on native species, and altering habitats. Feral pigs, descended from domestic swine brought to North America by European settlers, are a prime example. They cause widespread damage to crops and natural ecosystems through their rooting behavior and compete with native animals like deer and turkey for food. Their populations are widespread and difficult to control.
In Australia, feral cats have had a devastating impact on native fauna, preying on dozens of species of small mammals, birds, and reptiles and contributing to numerous extinctions. In the American West, feral horses, or mustangs, are descendants of horses brought by the Spanish. Their populations can overgraze sensitive arid lands, damaging vegetation and impacting water sources, which creates challenges for managing native ecosystems.