By Dr. Robert Thorson

Practically everyone has heard of the nursery rhyme “Humpty Dumpty,” and knows how it ends: “All the king’s horses and all the king’s men / Couldn’t put Humpty together again.” Indeed, many natural systems, once broken, can never be put back together again.

But this hasn’t stopped visionary conservationists from trying to reassemble the extinct passenger pigeon, one genetic trait at a time. Though I’m no specialist in ornithology, genetics or wildlife conservation, this sounds like a very bad idea to me, especially on ethical grounds. I don’t want to live in a world where Franken-birds substitute for those we senselessly destroyed before saying “oops.”

First, the facts. The passenger pigeon is one the best known extinctions in North America, and probably the most egregious cases of “shoot first, think later.” During the 19th century, billions migrated over the eastern United States in flocks so dense they darkened the skies. This gave sportsmen something to shoot at. The migrations also provided easy access to tasty protein for restaurant meals and family stewpots because the birds could be netted like aerial schools of fish. But as their numbers dwindled near the turn of the 20th century, some of the remaining pigeons were captured and kept alive in places like Cincinnati Zoo, where the last one died in 1914. Extinction.

Now there’s talk of bringing them back from the dead. Not as the real clone, but as a multi-species chimera, or a genetic collage, which was discussed in a news forum by Richard Stone published April 5 in Science. It describes a heated debate within the conservation community about whether this is a good idea. “Proponents say they are driven in part to right historic wrongs,” to atone for a shameful past. Opponents are concerned about the ethical choices involving what’s called “recreational conservation” and the potential harm to ecosystems. Should we say yes to resurrecting the ivory billed woodpecker because we think they’re magnificent? Should we say no to resurrecting the saber-toothed cats because they might stalk humans?

I’m not comfortable having lab scientists make those choices for me, doing what Mary Shelley’s fictional Dr. Frankenstein did, which was to create and release creatures into the environment. Would a reconstituted and reintroduced passenger pigeon be considered an invasive species? Would it disrupt the healing that’s already taken place? Would they be a vector for some new disease? Would the funding needed to accomplish this task undercut higher priorities elsewhere?

The good news is that the debate I’ve outlined pits wishful thinking against prudent caution. The technical genetic and behavioral obstacles haven’t been surmounted. No one has succeeded in cloning a living bird, much less an extinct one. This is why lab scientists are working on the radical, piecemeal alternative of splicing selected genes from a donor species like to the passenger pigeon to the framework genome of a closely related host species, in this case the band-tailed pigeon.

The first step is to reconstruct the entire genome from the extinct passenger pigeon, which will be the donor. This is an easily achievable task, given current technology and the plenitude of stuffed museum specimens. Second, we identify the salient genes in the donor we wish to attach to the host genome, for example the passenger pigeon’s orange-colored breast and long tail. Third, we sequence the host genome. Fourth, we splice the genes from donor to host. Fifth we figure out a way to get the newly spliced genome to reproduce through germ cells (sperm and egg). Sixth, and most challenging, we teach these chimera creatures to behave like the real birds of yore, which parented their hatchlings instead of killing them, and taught them to migrate from nesting to feeding grounds. The current plan is to use in-nest puppets and field training to support these essential tasks, respectively.

Given the technical challenges, I think our money would be better spent elsewhere than filling the skies with chimeras. The elsewhere I have in mind are programs that keep the memory of this bird holocaust alive.