In a letter to a friend on November 13th, 1789, Benjamin Franklin hedged his hopes for the newly minted United States Constitution with the now famous words, “…of course, nothing is certain except death and taxes.”

To death and taxes, one might add “extinction” to Franklin’s list of eternal certainties. Once a creature like the auroch or the dodo has vanished from the face of the earth — truly vanished, not simply gone AWOL, as in the case of the deep-sea Coelacanth or, one hopes, the Ivory-billed Woodpecker — it’s gone forever.

Or is it?

As a matter of fact, there are well funded international efforts underway to bring back some of the more popular extinct animals, like the woolly mammoth and the passenger pigeon.

Popularity is a key concept in the so-called “de-extinction” movement. No one — at least, no one in their right mind — would want to bring back a vanquished disease like smallpox or rinderpest, once it has finally been eradicated.

The passenger pigeon, on the other hand, an attractive and talented bird once so successful that it numbered in the billions, is an evolutionary loser that seems ripe for a “do-over.”

How does one go about resurrecting an extinct beast? First of all, you need a genetic sample. This is a lot easier to find for a passenger pigeon than it would be for a T-Rex, a la Jurassic Park. Passenger pigeons survived in captivity until 1914; stuffed or freeze-dried specimens found their way into many museum collections.

Once you have a bit of the extinct creature’s DNA, the next step involves finding the closest living relative, which will serve as a starting point for the recreation — the genetic scaffolding, if you will. In the case of the passenger pigeon, that would be the band-tailed pigeon.

The band-tailed pigeon happens to be an excellent genetic match for the passenger pigeon, but mapping the differences between the two species’ DNA is still a fantastically complex operation.

The scientists of the “Revive and Restore” project are wrestling with the mapping problem right now. They hope to have a working blueprint of the passenger pigeon genome within a few months.

But, as any contractor will tell you, a blueprint is just a pretty picture. Someone still has to build the thing.

Once they have the genetic blueprints in hand, scientists will still have to culture a band-tailed pigeon germ cell; synthesize the missing bits of passenger pigeon DNA; insert the synthesized passenger pigeon DNA into the living embryo of a band-tailed pigeon; and successfully breed several generations of the newly concocted pigeon.

Let’s just say, for the sake of argument, that all of this comes to pass. When the dust settles, and the world’s first passenger pigeon in more than a century coos into the waiting microphones, the scientists who created it will face a fundamental — and legitimate — question: is this resurrected Franken-bird truly a passenger pigeon at all?

Genetic makeup is only part of our story as living creatures: the “nature” part. But what about “nurture?” With no living parents to instruct the hatchling in the ways of the passenger pigeon; and with its natural ecosystem radically altered, or perhaps even completely gone, can any bird, even a genetically “de-extinctified” one, rightly be called a “passenger pigeon?”

The scientific community seems to be divided on this point. In fact, some conservationists think that the whole idea of “de-extinction” is a dangerous distraction. Biological extinctions are happening on a massive scale and at a frightening clip. The last thing the earth needs, in their opinion, is another reason for people not to take this global disaster seriously.

And I haven’t even touched on the question of ethics: i.e., whether it’s right to bring an animal back from extinction, no matter the means, even if it’s technologically feasible.

To my mind, the more pressing issue is a practical one: the potential risk to our own health as a species. Michael Crichton made precisely this point in Jurassic Park: nature is inherently chaotic, and our ham-handed attempts to create “designer animals” are bound to have unintended consequences.

You may remember that the creators of the dinosaur zoo in Jurassic Park thought they had a foolproof way to keep the animals from reproducing: they’d only make female dinosaurs! What they didn’t bargain for was that by splicing frog DNA into the dinosaur genome, they’d created a work-around for the dinosaurs. Some species of frogs have the ability to spontaneously change their sex, an evolutionary adaptation for times when one sex or the other predominates. In other words, by completing the fragmented dinosaur DNA with frog DNA, the scientists had created something entirely new: female dinosaurs with the ability to change into males, as needed. The population that they thought they’d neutered went on to produce very real dinosaur babies, and mayhem ensued.

I don’t envision a world where great herds of woolly mammoths run amok, or passenger pigeons go on cinematic rampages. But I am wary of the unintended consequences of gene splicing, whether in the form of the reconstituted genome of an extinct animal, or in the growth gland of a genetically modified farmed salmon.

Extinction may ultimately prove to be reversible, at least in certain limited cases, but I can think of another human certainty to add to Franklin’s list: hubris.