Claudio Sebastián Quilodrán Venegas

Biological invasions have profound impacts on biodiversity and ecosystem functioning and services, resulting in substantial economic and health costs estimated in the trillions of dollars. Preventing and managing biological invasions are vital for sustainable development, aligning with the goals of the United Nations Biodiversity Conference. However, some invasive species also offer occasional benefits, leading to divergent perceptions among stakeholders and sectors. Claims that invasion science overlooks positive contributions threaten to hinder proper impact assessment and undermine management. Quantitatively balancing benefits and costs is misleading, because they coexist without offsetting each other. Any benefits also come at a price, affecting communities and regions differently over time. An integrated approach considering both costs and benefits is necessary for understanding and effective management of biological invasions.

The worldwide expansion of modern humans ( Homo sapiens ) started before the extinction of Neanderthals ( Homo neanderthalensis ). Both species coexisted and interbred, leading to slightly higher introgression in East Asians than in Europeans. This distinct ancestry level has been argued to result from selection, but range expansions of modern humans could provide an alternative explanation. This hypothesis would lead to spatial introgression gradients, increasing with distance from the expansion source. We investigate the presence of Neanderthal introgression gradients after past human expansions by analyzing Eurasian paleogenomes. We show that the out-of-Africa expansion resulted in spatial gradients of Neanderthal ancestry that persisted through time. While keeping the same gradient orientation, the expansion of early Neolithic farmers contributed decisively to reducing the Neanderthal introgression in European populations compared to Asian populations. This is because Neolithic farmers carried less Neanderthal DNA than preceding Paleolithic hunter-gatherers. This study shows that inferences about past human population dynamics can be made from the spatiotemporal variation in archaic introgression.