Biological diversity is enhanced through human movement from "summary" of The Next Great Migration by Sonia Shah
Human movement has long been a driver of biological diversity. When humans set out from Africa some 60,000 years ago, they carried with them a suite of plant and animal species that would become the basis of agriculture in their new lands. As they colonized the world, humans deliberately transported their favorite species—rice, wheat, and cattle, among others, which they used to transform the ecologies they encountered, altering habitats and creating new niches that encouraged diversity. Humans also inadvertently carried with them species that would become invasive, outcompeting native ones and sometimes driving them to extinction. But even as humans contributed to the extinction of some species, they helped to diversify others by inadvertently creating new habitats that favored the survival of certain species over others. In this way, human migration has shaped the diversity of life on Earth, often in unexpected ways.
The movement of people has allowed species to mingle in new combinations, producing novel genetic variations that can allow populations to adapt to changing conditions. As people migrated across continents, they brought with them the seeds of plants that had evolved in one place and were now being introduced to another. These plants—wheat, rice, corn, and more—crossed with related species in their new homes, creating new strains that were better adapted to local conditions than their ancestors.
Human movement has also facilitated the spread of diseases, which can have devastating effects on ecosystems by driving down the populations of certain species. But it has also helped to spread beneficial microbes, which can enhance the resilience of ecosystems by providing new functions or capabilities. Thus, human migration has been a double-edged sword for biological diversity, both harming and helping the web of life on Earth.
