Geography Reference
In-Depth Information
homes, and restrictions on redeveloping portions of the city—especially
places where buildings do not currently exist, so-called browni eld sites—are
needed if the sparrow is to once again thrive in its ancestral subirdia.
Rapid, explosive evolution in response to the novel environments humans
create is the new normal. The process that adjusts species to this dif erent
land has a name: contemporary evolution. It began in earnest during the In-
dustrial Revolution. In the latter half of the eighteenth century, cities such as
Manchester, England, were sooty from coal-i red textile mills and coal-burning
stoves that heated the homes of around a half million people. Coal's waste—
carbonic and sulfuric acids—poisoned the air, sickening humans and killing
most aquatic life. People expected to live barely forty years. Only house spar-
rows, starlings, and pigeons occupied the city center. Industrial England was
dark, so natural selection stepped up its pace and darkened the life that remained.
The peppered moth rests motionlessly on the trunks of trees during the
day, having l own and foraged all night. Its sole defense from its bird preda-
tors is to expertly match the color of the surface upon which it rests. Mostly
white with l ecks of dark, the most common form of the moth was well camou-
l aged against preindustrial English trees that stood white as birch, thanks to
an encrusting skin of lichen and bryophyte. When coal pollution killed the
bright epiphytic crust and blackened the trees with residues of soot and smoke,
the white moths were easy meals for starlings, sparrows, and the occasional
jay or robin. The occurrence of light-colored moths plummeted, but a melanic
form of the species quickly gained prominence. Butterl y collectors documented
the result of this natural selection. The population of moths had evolved to
match its new urban environment in response to predation. A variety of other
moth species as well as spiders, ladybird beetles, bark lice, and pigeons all
followed suit.
