Passenger pigeons are now extinct, but the species could be brought back to life, per scientists.

The species vanished from the Earth 100 years ago, but passenger pigeons were once common throughout the United States. Using DNA, researchers may now be able to revive species that have not been seen on Earth for decades.

Revive and Restore is a new group aimed at bringing extinct species back into existence.

"De-extinction" candidates include the passenger pigeon, woolly mammoth, and the dodo. Genetic code decays over time, so bringing dinosaurs back to life as in "Jurassic Park" is unlikely to happen soon.

In the 19th century, biologists estimated there were roughly 5 billion passenger pigeons in existence worldwide. They swarmed in vast quantities, and tales were told of the animals blacking out the sky.

People hunted the species for food, and this close swarming behavior made them easy prey for hunters. At the start of the 20th century, the animals were completely eliminated from the wilderness. Just one individual animal remained; a 29-year-old female at the Cincinnati Zoo named Martha. That last specimen of the species died in 1914.

"The DNA of many extinct creatures is well-preserved in museum specimens and some fossils. Their full genomes can now be read and analyzed. That data may be transferable as working genes into their closest living relatives, effectively bringing the extinct species back to life," Revive and Restore officials wrote on its website.

The group was founded by self-described "serial entrepreneur" Ryan Phelan and Stewart Brand, co-founder of the Global Business Network.

Revive and Restore has already gathered viable DNA from remains of passenger pigeon. This genetic code could be enough to make the passenger pigeon the first species ever to come back through de-extinction.

The process would begin by breeding band-tailed pigeons, a close relative to the passenger pigeon. Pieces of DNA would then be inserted into the genetic code of the animals, slowly turning the population into the first live passenger pigeons seen since the opening days of World War I.

That last pigeon, Martha, and her ilk may someday have descendants if efforts are successful. Martha's preserved remains have been kept at the Smithsonian Institution for 100 years.

The body is being taken out of storage and displayed as part of an exhibit, reminding people of the possible effects of humans on wildlife. The display opens June 24, but not without controversy. Critics of de-extinction claim the ability to revive vanished species will discourage conservation efforts.

"It's very negative, very expensive and not going to achieve any conservation goal as far as I can see," David Ehrenfeld, Rutgers University biologist, told the press.

If Revive and Restore succeeds in its mission to bring back the passenger pigeon, Martha will not be the last member of her species.

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