Differences in physical traits between human populations accumulated slowly over tens of thousands of years. As people spread across the globe and adapted to local conditions, a combination of natural selection and cultural innovation led to physical distinctions. But these groups did not remain apart. Contact between groups, whether through trade or conflict, led to the exchange of both genes and ideas. Recent insights from the sequencing of hundreds of thousands of human genomes in the past decade have revealed that our species’ history has been punctuated by many episodes of migration and genetic exchange. The mixing of human groups is nothing new.
What is new is the rate of mixing currently underway. Globalisation means that our species is more mobile than ever before. International migration has reached record highs, as has the number of interracial marriages, leading to a surge of multiracial people such as Shewmake. While genetic differences between human populations do not fall neatly along racial lines, race nevertheless provides insight into the extent of population hybridisation currently underway. This reshuffling of human populations is affecting the very structure of the human gene pool.
People today are more likely to live in an environment for which they are not biologically well-suited. If the history of life on Earth can teach us anything, it is this: as conditions change, species either adapt or become extinct. In our time of considerable environmental change, humanity should consider its options. No species, even the almighty Homo sapiens, can stop evolution completely. But we can choose to limit our capacity for ongoing biological adaptation in an effort to remain ever the same by keeping populations isolated. Of course, such decisions are not made by humanity as a whole but by individuals and governments. Nationalism and xenophobia, on the rise in the US and Europe, threaten to decrease genetic exchange between populations, stifling our ability to continue evolving and adapting.
Alternatively, we can embrace immigration and globalisation in an effort to position ourselves for a brighter future. The underlying causes of the current high rates of human migration are likely to persist, and perhaps to increase, as the global human population continues to grow. Access to natural resources such as fresh water have long driven population movements, and these might become even more important drivers of migration as the world’s population expands. Likewise, as economic development proceeds, the amount of resources used by each person will continue to rise, putting further pressure on scarce resources and further motivating people to move in search of better conditions. Sea levels are expected to continue rising as a result of global climate change, and this is likely to drive large-scale population movements away from low-lying coastal areas as they become uninhabitable. In short, the reshuffling of populations that results from the movement of people around the world will continue to shape the structure of our gene pool – and, by extension, our future evolution – for many generations to come.