Environmental Engineering Reference
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late eighteenth century. Already the migrants have developed reproductive incompatibility with their
cousins back home. They are, in effect, a new species. Similarly, European house sparrows have grown
apart from their forebears since arriving in North America in the mid-nineteenth century.
11
And sockeye
salmon in Washington State turned into a new species within fifty-six years, or thirteen generations, of
their introduction to new lakes. Nature doesn't hang about.
12
Native species evolve too, so they can take advantage of new arrivals. A new hybrid of the
Rhago-
letis
fruit fly in North America has developed the ability to colonize invasive honeysuckles, while its
parent species continues to feed on native plants.
13
All this will happen more and more often as a result
of alien introductions, says Thomas. “Evolutionary origination is accelerating, as populations and spe-
cies evolve, diverge, hybridize, and speciate in new surroundings,” he wrote in the unpublished original
version of his
Nature
paper.
Those who fear alien species also often fear hybridization. Simberloff calls genetic mingling
between natives and aliens “a sort of genetic extinction.”
14
He says that a “hybrid swarm” will take out
the pure natives and cites the case of Canada's ruddy duck's cuckolding with Europe's white-headed
duck. Another example is Scottish wildcats interbreeding with feral domestic cats. Such swamping can
happen, agreed Thomas. “But new genes from alien species usually only invade the genome of an ex-
isting species if they confer some advantage. They often help them thrive.” This is nothing more than
Darwinian survival of the fittest, he argues. We should look at what is gained, not what is lost.
Hybridization can turn minnows into monsters, but it can also create new species, new diversity, and
new virtues. If we want to encourage evolution, we must embrace successful alien species. In a world of
fragmented and abused nature, with many species under threat, nature needs them.
Thomas accepts that we will sometimes recoil at the kind of dynamic and unpredictable change he
is talking about. “Things are happening so fast that we see ecological transformations in our individual
lifetimes,” he tells me. “It is human nature to be worried about that. I sometimes pull up alien weeds
that I see in the fields around where I live. But that is an emotional response. Intellectually, I see noth-
ing wrong with most of them.” We should, he said, “not confuse change with damage or think of alien
species as bad and natives as good.” Nature is always changing and adapting. Species are going to have
to move to survive, whether in the face of climate change, other human activity, or simply the ongo-
ing change that constantly marks out nature. “A narrow preservationist agenda will reduce rather than
increase the capacity of nature to respond to the environmental changes that we are inflicting on the
world,” he said. “We need to think less about keeping things just the way they were—because it is im-
possible—and more about promoting the new.”
15
This amounts to the beginning of a manifesto for the new wild. It has many adherents. Christoph Kueffer
of the Swiss Federal Institute of Technology in Zurich says novel ecosystems “represent the wild lands
of the future, the self-organized response of nature to anthropogenic impacts.”
16
“There is no point in
debating what is natural and what is novel. It is all novel,” he says. The traditional idea that biodiversity
was “conserved most effectively by protecting nature from human influence does not work any longer.
Humans and their impacts are omnipresent; a new paradigm is needed for guiding conservation action.”
Conservationists invest their time and money to fight what he calls “the ghosts of past invasions,
always one step behind.” In doing so, said Kueffer, they “increasingly run the risk of preventing the
introduction of species that would be useful in the new circumstances.” Martin Schlaepfer of the State
University of New York agrees. “Any conservation strategy that eradicates species simply because they
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