Last winter, a group of scientists met at Harvard Medical School to discuss restoring the passenger pigeon (Ectopistes migratorius) to its natural habitat. What was remarkable about the event is the North American bird, which once numbered in the billions, is extinct, and has been for nearly a century.
Now, researchers believe they have the technology to bring the pigeon and other extinct species back into existence. And while that’s great news for many conservationists the success of such an endeavor will depend on more than just genetics and advances in cloning.
The passenger pigeon’s habitat – made up in large part by American chestnut trees – was largely destroyed by blight, imported in Asian wood or chestnut trees. Without food to sustain the bird it would be futile to bring it back for any reason other than pure scientific study. But recent news from the American Chestnut Foundation (ACF) is hopeful.
A Tree for the Ages?
Since the 1980s the ACF has used a method called “back breeding” to create a potentially blight-resistant tree. When the pigeon takes flight there may well be the first generation of backcross bred “Restoration Chestnuts” waiting, and capable of bearing nuts.
The American chestnut once numbered four billion (or roughly one tree out of every four in eastern forests). The one hundred foot towering tree- an individual tree that stood near Waynesville, North Carolina measured 17 feet across- was reduced by blight that arrived from Asia (probably China) in the early 20th century to an understory shrub that seldom flowered.
By the 1950s the chestnut’s expansive range, which once stretched north from Maine to Georgia in the south, and bulged east from the Chesapeake Bay to the Ohio Valley in the west, was reduced to barely a half breath.
“Imagine that the world’s human population was reduced to the size of Chicago, and all that remained were children and teenagers – no adults,” said Paul Franklin, director of communications for the ACF.
“That’s the scope of the disaster that befell the American chestnut, and it’s been called the greatest environmental disaster of the 20th century.”
In 1983 a group of scientists formed the ACF, and decided to use a process called backcross breeding to create an American-Chinese hybrid. They then bred that tree back with American parents until they achieved a tree that was 94% American with blight resistance inherited from its Chinese parent.
In 2005, the ACF announced they had a first generation of 500 blight resistant seeds. Franklin said the foundation’s annual seed production has grown to over 12,000 and volunteers have planted over 300 breeding orchards across 19 states. There are also 10,000 potentially blight resistant trees planted in national forest lands.
“The purpose of the regional orchards is to create trees that have both great genetic diversity and regional adaptation,” said Franklin. “You need a hardy tree with genetic diversity. Otherwise it’s like turning a child loose without supervision. Think of what could happen.”
Chestnut Giants – Courtesy of The American Chestnut Foundation
The foundation’s main Meadowview, Virginia breeding facility contains over 60,000 trees at various stages of development, including B3F3’s or trees that have been backcrossed and interbreed for six generations. Franklin said the ACF expects 60-80 percent of the trees to survive to maturity in the wild with about 20 percent showing no sign of blight whatsoever, and eventually growing as strong and tall as their ancestors. Even those trees that are infected should live long enough to produce nuts.
“If you have a sunny spot, they will grow,” Franklin said. “Some will show some blight damage, but most will live and produce beautiful sweet nuts that humans, animals and, yes, passenger pigeons love.”
Martha- The Last of Her Kind
The last known passenger pigeon was named “Martha,” after the former first lady, Martha Washington. The bird lived out her final days as part of an unsuccessful captive breeding program at the Cincinnati Zoological Garden.
The pigeon was stunning, having a blue head and scarlet eyes. According to ornithologists passenger pigeon flocks measured a mile wide and up to 300 miles long.
In 1813 John James Audubon famously described viewing flock after flock of passenger pigeons fill the sky.
“I observed the Pigeons flying from north-east to south-west, in greater numbers than I thought I had ever seen them before… the birds poured in in countless multitudes…. The air was literally filled with Pigeons; the light of noon-day was obscured as by an eclipse… the continued buzz of wings had a tendency to lull my senses to repose.”
The passenger pigeon population constituted up to 40 percent of all birds in the United States. With the advent of the telegraph hunters realized they could send messages ahead of oncoming flocks. The population’s numbers- as many as six billion– plummeted and the species expired within 100 years.
After Martha’s death conservationists took concerted action to protect other species close to extinction, chiefly the iconic American Bison.
The plains (Bison bison), also known as the American Buffalo, and wood Bison (B. b. athabascae) once numbered 40 million, but overhunted, its population dwindled to 1,091 in the early 1900s. In 1907, the Bronx Zoo joined with the American Bison Society and reintroduced 15 Bison to the Wichita Forest Reserve in Oklahoma. Today because of the catastrophe that happened to the passenger pigeon there are approximately 450,000 in Mexico, the U.S. and Canada.
A Plan to Reverse History
The American chestnut and bison were heavy on the mind of Stewart Brand last January during the Harvard Medical School meeting, which he co-convened. Brand is a man who is perhaps better known as the founder of The Whole Earth Catalog than as someone who entertains notions of rebuilding long gone species. But in the last several years he’s says he’s been very aware and interested in thinking in the long term.
As co-founder and president of The Long Now foundation, Brand proposes human beings think and plan in terms of the far future, 10,000 years to be exact. With that in mind, the foundation’s Revive and Restore program plans to continue to bring together de-extinction experts from all over the world to consider restoration techniques that include cloning, homologous recombination, and back-breeding.
During the daylong conference the group considered several questions, including which species they could successfully clone, including Woolly mammoths, European aurochs, Pryrenean ibex, and others. They discussed probably time frames, habitats, cost and sustainability, as well as ethical questions such as the meaning of reintroducing species into an unfamiliar world.
When I asked Brand if he was concerned about people’s readiness to live with species that fall far out of the scope of modern day reality, such as a mammoth, he was nonplussed.
“We’re more comfortable at getting in to the guts of how life progresses – that is, genetics – than we used to be,” said Brand. “It’s gotten so inexpensive that anyone can do it. We want to ask all the questions now, since recent developments in biotechnology enable scientists to reconfigure genetic code much faster and at a much greater reduced cost than in the past.”
Brand said genomic analysis of degraded ancient DNA (found in museum collections of all places), viable cells from different frozen “zoos” around the world – the San Diego Zoo has about 400 different species – as well as backcrossing genes with similar related species living today will also enable scientists to better protect endangered species.
“We’ll learn what caused the extinction and we’ll be able head off future extinctions,” said Brand.
Because the passenger pigeon has a closely living relative, the the band-tailed pigeon, Brand said the decision was made to study its genome. The mammoth would come… later. The cloning of a mammoth, which is closely related to modern day elephants, is possible, but it would mean a far lengthier gestation period and process. A mammoth calf to a mammoth calf cloning process- until you have a fully genetically encoded calf- would take 24 years, compared to a passenger chick to passenger chick process, which Brand says would take six months.
“The passenger pigeon appears to be easy to work with,” said Brand. “It’s a lot easier to get into a pigeon egg than an elephant egg.”
Tinker… Tinker… Tinker – Restore
Ben Novak, a graduate student interning with the Revive and Restore program, is working at George Church’s bio-engineering lab at Harvard to refine the DNA sequence data from three passenger pigeon specimens.
“We want to learn about the process with precision and what is the cost and what are the stages,” said Brand.
At the same time, Novak will work to sequence DNA from the mourning dove— which the nonprofit cites as a possible hybridizing species with the passenger pigeon. Next, Brand said they’ll compare the data with the passenger pigeon genome to improve the quality of what they already have from the passenger pigeon.
“The pigeon is a keystone eastern deciduous forest species,” said Brand. “If the American chestnut comes back we might have a serious continental scale comeback for both from the Mississippi to the Atlantic. I grew up in Illinois and I’d like to see what the original forest might have looked like.”
While the bison was saved by conservation efforts, for the time being, the passenger pigeon has been relegated to a verbal memory that’s traveled down through generations to people like my father who’s grandmother witnessed the dense flocks passing over her rural home in Purcellville, Virginia. When science gives both the passenger pigeon and the chestnut tree a second chance at life it may well be the first time that verbal memory becomes tangible reality.
Marina Cords, a Columbia professor of anthropology in the department of Ecology, Evolution and Environmental Biology, recently coauthored a study of biodiversity in tropical rainforests that was published in Nature (July 2012). In an assessment of over 30 different categories of species, researchers found that about half of the forest reserves were “struggling to sustain their initial biodiversity” … and that “a failure to stem broad-scale loss and degradation of such habitats could sharply increase the likelihood of serious biodiversity declines.”
The decline of the earth’s ecosystems call for the same urgent action as Martha’s death inspired nearly one hundred years ago. That bet paid off big and saved the American buffalo. Today we find ourselves on a heady new path to sustainability. This time second chances are frozen in time – nitrogen to be exact – and are ready for withdrawal. All bets are on.