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evolution of a new species from its ancestors that results from the gradual ac-
cumulation of isolating dif erences over time. Certainly we are already cultur-
ally distinct from our ancestors, but most biologists would not consider this
adequate to proclaim that we are truly a species apart from ancestral
Homo
sapiens.
They would require more lasting distinctions that make our DNA
incompatible with that of our ancestors.
I have no doubt that our new niche and culture are, in fact, promoting ge-
netic changes. As we prefer mates with new physical or cultural features, chal-
lenge our brains with the demands of new technologies, expose our metabolic
processes to new diets, and succumb to new mortality agents, we expose our
populations to new selective pressures that are capable of causing genetic,
evolutionary change. Old foes such as dim eyesight, dull hearing, disease,
and physical deformities no longer doom us to a short life with a reduced
chance of reproduction. In their place are new hazards of urban life: fatty
foods, carcinogens, inactivity, automobiles, and stress. And therefore, it is
only a matter of time (and I doubt very much time) before our new lifestyle
leads to speciation. Thus far, only about 250 generations of humans have been
exposed to the rigors of urban life—an icing on the cake of our evolutionary
history, as eminent evolutionary biologist Jerry Coyne points out. But I con-
tend that this icing is an inl uential force signii cantly distinct from our earlier
300,000 generations of hunting and gathering that is able to shift our evolu-
tionary trajectory. The day is near when we are no longer
Homo sapiens
(wise
person) but instead something entirely new. Perhaps we are already
Homo ur-
banus
(city person).
As urban people we live in a time when everything changes rapidly. Gone
is the Holocene, the geologic period that succeeded the Pleistocene, or ice
age, twelve thousand years ago. Then, the climate was stable and life changed
slowly. We now live in the Anthropocene—a period of chaotic change initi-
ated by humans several millennia ago. Our fellow creatures quickly adapt,
