In April 1896, a flock of American passenger
pigeons was discovered nesting in a forest
outside Bowling Green, Ohio. Once the most
 ubiquitous bird in North America, the passenger
 pigeon had shrunk from countless billions to this
 single of flock of 250,000. News of the find was
telegraphed across the country, drawing hundreds
 of visitors to the area.
By this time, the great bison—a powerful symbol
of frontier America—had dwindled from a population
 of tens of millions to just a few hundred, all in zoos
 or reservations. Determined to prevent a similar
fate for the passenger pigeon, several states had
already enacted hunting bans. Seeing the birds
gave conservationists hope that the restrictions were
Thomas Fuchs

Unfortunately, the visitors to Bowling Green
weren't bird watchers but hunters, and Ohio
 had no such protective laws. They killed the
 entire flock in a day. Afterward, the train taking
 the carcasses to sell in New York City derailed,
leaving them to rot in a ravine. Eighteen years later,
 the lone survivor of the species—a female bird
named Martha, after George Washington's wife
—died in a cage in the Cincinnati zoo.
The death of Martha is part of a much larger story
 that has been dubbed the Sixth Extinction. (The
 term was coined in the 1990s by the Kenyan
paleontologist Richard Leakey ; it has been used
widely ever since, as in the title of Elizabeth Kolbert's
 well-reviewed recent book.) The previous five waves
 of extinctions began in the Ordovician era about 440
 million years ago, when global cooling led to the Earth'
s first intense ice age. A simultaneous drop in
 temperatures and sea levels brought about the
extinction of up to 88% of all species.
But even this paled by comparison to the catastrophic
 death toll during the third wave—the Permian extinction
—approximately 250 million years ago. In what's often
 known as "the Great Dying," megaton volcanic eruptions
 covered the planet with noxious gases, starting a chain
reaction that scientists estimate ultimately led to the
extinction of some 97% of the species on Earth. The
 wave that killed off the dinosaurs some 66 million years
ago in the late Cretaceous period—involving yet more
volcanic eruptions, perhaps coupled with a large
asteroid hit—was just a pale copy.
The Sixth Extinction actually started tens of thousands
 of years ago, when Homo sapiens discovered how to
 hunt the lumbering mammals that then populated the
 Earth: the mastodon, the giant sloth, the woolly
mammoth and more. By the time the first human
settlements were in evidence in 10,000 B.C., these
 mammals were gone.
Charles Darwin mistakenly believed that extinction
was an immensely slow and evolving process,
regrettable but natural. But by the time his "On the
 Origin of Species" was published in 1859, the
inhabitants of North America were already well
on their way to accomplishing a mini die-off that
would result in the loss of an estimated 1,000
species in just 500 years—including the colorful
 Carolina parakeet, the Merriam's elk, the Rocky
 Mountain locust and the hapless passenger pigeon.
Today, the World Wildlife Fund estimates that
3,879 species live under imminent threat. Among
 them are African elephants, whose ivory tusks
are so sought-after in China that the current rate
of poaching could lead to their extinction in less
than a decade.
The problem with the term Sixth Extinction is that
 it implies a sense of inevitability, as though humans
can't help being dangerous, like the weather and
 large asteroids. Yet the example of Theodore
Roosevelt shows that a man (or woman) can halt
 inevitability in its tracks. The 26th president couldn't
 save the passenger pigeon, but he did help rescue
the great bison by creating four national game reserves.
 He also protected 150 national forests, 51 bird
reservations and 230 million acres of pristine land.
We don't need to hug a tree or kiss a toad, but we
 should all stand up for the Marthas, big and small.