This chapter examines the evolutionary influences of human activities, and considers the proposition that many species are threatened with extinction.

Humans: as animals practising extreme niche construction

Anatomically modern humans arose in Africa over 100 000 years ago, and by 40 000 years ago they were perhaps fully human in anatomy, behaviour and language (Diamond, 1992). Increasingly, as humans have migrated to almost all parts of the globe, they have influenced, modified, managed or transformed all the Earth's natural ecosystems by practising what has been termed ‘niche construction’.

Leland (2002) notes that, traditionally, ‘adaptation typically is regarded as a process by which natural selection molds organisms to fit a pre-established environmental template … yet in varying degrees, organisms choose their own habitats, choose and consume resources, generate detritus, construct important components of their own environments … destroy other components and construct environments for their offspring. Thus, organisms not only adapt to their environments but in part also construct them.’ In the case of humans, niche construction may be seen, therefore, as an evolutionary strategy that aims to maximise survival and reproductive success.

Human environmental activities through the development of cultural practices have many intentional effects. As Western (2001) observes, ‘the most universal and ancient features of our “humanscapes” arise from a conscious strategy to improve food supplies, provisions, safety, and comfort – or perhaps to create landscapes we prefer, given our savanna ancestry’. He points out, however, that there are many unintended side effects of human activities that lead to a multiplicity of consequences at every spatial scale, and his list includes: habitat and species loss; loss of keystone species; major changes to ecosystems resulting in reduced ecotones; truncated ecological gradients and changes to soils and accelerated erosion; introductions of invasive non-native species and diseases; side effects of fertilisers, pesticides, herbicides; over-harvesting of natural resources; nutrient leaching and eutrophication; pollution of soils, water and air; and ‘global changes to the lithosphere, hydrosphere, atmosphere and climate’.

Human impact on the environment

The formal geological term for the last 11 700 BP years is the ‘Holocene’, but human niche construction has become so universal and dominating that the present era has been called the ‘Anthropocene’ (Ruddiman, 2013). There has been a great deal of debate about when this era might have begun.