- In the first two chapters of The Origin of Species, Charles Darwin contrasted selection upon variation under domestication and under nature. The distinction is becoming increasingly blurred, with humans selecting for variants across all species that best tolerate the environmental conditions that we impose. Here, I discuss several unintended selection pressures that are altering the evolutionary trajectory of life on Earth (intended selection pressures, e.g. through antibiotic application or selective breeding, are not discussed). My goal is not to give an exhaustive list, but to highlight the range, potency and idiosyncrasy of selection pressures induced by humans (figure 1; see also [19] and references therein).
Figure 1.
Human-altered selective forces. (a) Selection in built environments: feathers left on a window illustrate the high death toll of birds colliding with buildings and automobiles [12], selecting against migratory behaviour [13] and for manoeuvrability [14]. (b) Selection to avoid hunting or harvesting: humans target individuals with preferred traits, selecting against traits such as long ivory tusks [15]. (c) Selection in novel communities: both abiotic and biotic selection pressures are reshaped when humans bring together species in new assemblages, as found in cardinals nesting in introduced honeysuckles [16]. (d) Selection on dispersal: fragmented landscapes select for individuals that can remain in hospitable environments, favouring non-dispersing seeds in Crepis sancta [17]. (e) Selection on inheritance systems: rapid evolution associated with human cultivation can alter the genome, with increased recombination rates and polyploidy found in many domesticated plants, such as oats [18]. Photographs: (a) Alan Hensel; (b) Sarah Otto; (c) Jeff Whitlock; (d) Susan Lambrecht; (e) Henrik Sendelbach.