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without any regard for nature's balance. This looked more like the world of Gleason with added math-
ematics.
The battle between the two camps is partly about the right to claim the legacy of Darwin. Clements
and his successors had long argued that natural selection would produce their climax ecosystems. But
the individualists and chaos theorists pointed out that, unlike Lamarck, Darwin never believed that evol-
ution delivered any kind of perfect order or natural balance. “One of the basic tenets of Darwinian evol-
ution,” said May, is that “all animals have the capacity to do more than replace themselves. . . . The
result is that most populations of plants and animals usually fluctuate.”
15
Evolutionary biologist Steph-
en Jay Gould wrote that “the Darwinian mechanism includes no concept of general progress or of op-
timization.”
16
Darwin held that natural selection allowed species to adapt to changing local environ-
ments—and that was all. Ecosystems were not perfect or imperfect, good or bad, healthy or sick. There
was no goal, no “climax,” no perfect model against which they could be measured. They just were.
Gould, a New Yorker, was one of the great evolutionary biologists of the twentieth century. He is
most famous for his ideas about “punctuated equilibrium,” holding that evolution wasn't a continuous
process but happened mostly in bursts after major disruptions such as asteroid hits or super-volcanic
eruptions. Gould said ecologists were wrong to see anything innately superior about stable ecosystems
because disruption was essential to evolution. It provided chances for new species to evolve. Similarly,
the notion that “native must be best, for native has been honed to optimality in the refiner's fire of Dar-
winian competition” was a “pervasive misreading of natural selection,” and an “evolutionary fallacy.”
17
Species are not coevolved to fit niches; they are free to do as they will. Species evolve to get by, not
to attain Clementsian perfection. If another species comes along that fits in better, it will supplant the
incumbent and become the new “native.” Or they might carry on together.
Gould pointed out that Darwin had always been fascinated by this chaos of evolution and the role of
alien species in it. The great man once wrote to a sailor who had been shipwrecked on Kerguelen Island,
a French outpost in the Indian Ocean, to ask if he remembered seeing any seeds growing from driftwood
on the beach. Darwin wrote several papers on how seeds crossed the oceans on rafts of vegetation, in the
guts of birds or in mud caked on their feet—“patterns of colonization [that] reflect historical accidents .
. . and not a set of optimal environments,” as Gould put it.
18
The new generation of ecologists making the case for rethinking aliens has taken up these themes.
They argue that if ecosystems are open and dynamic, then aliens have as much right as natives to join
in—and can be just as useful. “Nativeness is not a sign of evolutionary fitness,” says Mark Davis of
Macalester College, a leading critic of the idea that there is something unfit about aliens. “Don't Judge
Species on Their Origins,” he titled one paper. Doing so, he argued, said more about humans and their
cultures than about species and their ecosystems. “Classifying biota according to their adherence to cul-
tural standards of belonging, citizenship, fair play and morality does not advance our understanding of
ecology.” Alien species can sometimes be nasty, but so can natives. There is, he believes, a pervasive
“indoctrination” in the science community that builds negative stories about alien species. Aliens are
vilified for driving natives out. They are irredeemably “other.” But this dichotomy has no basis in scien-
ce and should be ditched.
19
If the debate about ecosystems and aliens is, as Davis says, cultural, then it is also political. And the
politics is quite toxic. Gould compared Clementsian ecological ideas about perfectible ecosystems with
theories that arose around the same time on eugenics, a social philosophy of improving human genetic
traits first developed by Darwin's half-cousin Francis Galton. The parallels are striking. The adherents
of both ideas claimed to have their origins in Darwin's theories, both directly translated their scientific
theories into a view about how the world should be run, and both had a disturbingly xenophobic world-
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