Humans had begun to engage in activities that has led to the alterations in the distributions of a vast array of species across most, if not all, taxonomic groups by the Late Pleistocene, a new study published today on PNAS confirms ( PNAS, Special Feature: Perspective, 7 June 2016 vol 113 no 23). It’s important to note that “changes to biodiversity included extinctions, extirpations and shifts in species composition, diversity and communities structure”. Authors explain how the human ability to reshape global biodiversity is not a result of contemporary civilization : “the evolutionary trajectory of Homo sapiens has seen an exponential increase in the scope and impact of human niche constructing activities that have culminated in fundamental changes to planetary ecosystems”. The authors’ insight into microfossils and ancient DNA reveals “a pattern of significant long-term, anthropogenic shaping of species distributions on all of the Earth’s major occupied continents and islands (…) Few, if any, regions can be characterised as pristine. Extinction has been the starkest of these anthropogenic impact, but widespread changes to species abundance, composition, community structure, richness, and genetic diversity as a result of human niche construction are also increasingly demonstrable and of equally lasting impact”.
In settling the Planet, a lot of species stopped being only wild and became domesticated, invasive, commensal and pathogenic. “Diverse archeological assemblages from Africa, Europe and South Asia document the Late Pleistocene appearance of small, quick and difficult-to-catch game, such as fish, birds, rabbits, rodents and monkeys, that may signal anthropogenic impacts to resource availability. Other studies document decreases in the size of certain species as limpets and tortoise that may also reflect resource overexploitation”. We can see the same pattern in the current hunting for bushmeat in Angola ( find more at: UNEP : Angola, bushmeat trade threats eco-tourism ) and South East Asia. One of the main traits of Homo sapiens is the trophic plasticity related to cultural schemes.
But this study remarks also the importance of enormous urbanised settlements that have been creating interrelated networks of trade, economies, social interactions on a global scale. Cities are hot spots of the niche construction ability because they elaborate mindsets that indirectly affect ecosystems and species diversity. And defaunation too is an expression of it. “Defaunation is another enduring legacy of ancient human activities. The emergence of socially stratified urban societies in the Near East and Egypt, for instance, was linked to the extirpation of a number of wild animal species (…) Equus hemionus, Gazella subgutturosa, Alcelaphus buselaphus, Orix leucorix, Struthio camelus were all extirpated largely from ungulat mass kills. Ancient urbanisation contributed to a major reduction in large-bodied mammal species in Egypt, from 37 in Late Pleistocene/Early Holocene to only 8 today”.
One of the main point of the study is the striking link between present-day patterns and past-days patterns, that means we must think extinction processes historically and over time. “Most landscapes are palimsests shaped by repeated episodes of human activity over multiple millennia “( E.Ellis et al. quoted from 2013, Used planet: a global history, Proc Natl Acad Sci USA 110 (20): 7978-7985). The second remarkable point is that the speed of the process – it worked by pauses and accelerations – is both culturally and ecologically determined. But the third point crucial to our understanding of the problem – maybe the most relevant point – is that the dramatic change in species distribution across the globe has been the key factor to sustain an even bigger human population.
So, after two thousand years of evolution, can we still imagine a place for animals ? And is the common concept of species still relevant to us ?