To Rise From the Dead

“Extinction,” as they say, “is forever.”  It is the threat that has launched a thousand environmental campaigns. Despite being the ultimate fate of all species, extinction remains universally appalling in its finality. The thought of extinction serves as a chilling reference point for almost all conservation thinking.

Technologies being developed in the emerging Plastocene epoch promise to rewrite some of the most elemental truths of this earth. One of these truths is this bedrock claim about extinction.  Extinction, some biotechnologists think, is no longer forever. It can be reversed. Species can be brought back from the dead. The ethics that lurk within this possibility are nearly as stunning at the technology itself.

The end of the nineteenth century was not a good time for North American wildlife. Of the numerous catastrophic declines in wildlife populations during that period – think of wolves, bison, grizzly bears, and countless others – one of the most startling was that of a bird that never quite possessed the charisma to inspire a successful conservation story.

The passenger pigeon (Ectopistes migratorius) was an elegant, if not classically beautiful bird. It weighed in at just under a pound and stretched an unimpressive 15 inches from the tip of its beak to the end of its tail feathers. This relative of the rock and band-tailed pigeons commonly seen today in many city centers was in certain respects a somewhat unremarkable bird. In others respects, however, Ectopistes migratorius was one of earth’s most extraordinary phenomena.

In its mid-eighteenth century heyday, the passenger pigeon was an unimaginably prolific bird with a North American population of somewhere between 3 and 5 billion. (To give a sense of this number, if you placed just one billion of them in a line with the tip of one pigeon’s beak touching the end of the next pigeon’s tail, the line would circle the earth at the equator more than nine times). The birds gathered in gigantic flocks that were said to have darkened the sky. Early environmentalist John Muir reported seeing flocks of pigeons heading south in the fall so large that “…they were flowing over from horizon to horizon in an almost continuous stream….like a mighty river in the sky, widening, contracting, descending like falls and cataracts, and rising suddenly here and there in huge ragged masses like high-plashing spray.”

When they alighted in the deciduous forest to roost at night, huge branches would come crashing down under the weight of the birds. In the morning, the forest floor would be painted in a layer of fertilizer from the excretions of millions of digestive tracts. When flocks flew by, it was said you could kill birds by simply throwing a potato skywards or waving a long pole.

It is a sobering fact that a voracious market for bird meat, the desire to protect crops, and the clearing of thousands of square miles of forests for agriculture reduced passenger pigeon numbers from several billion to just a single bird by the early twentieth century. Like the story of the bison unfolding at about the same time, it was carnage on an astonishing scale. But unlike the bison, the killing did not stop in time. That one remaining pigeon, named “Martha” by her handlers, died a lonely death in a Cincinnati Zoo in 1914.

Would it ease our collective conscience if somehow we could bring this bird back from the dead? Scientists working with an organization called Revive and Restore certainly think so.

Martha’s carcass and those of several dozen other passenger pigeons were conserved in museums as items of interest to natural historians. Thanks to the genome reading techniques that have become commonplace in the last decade, tissues extracted from these carcasses allow for a pretty good read of some of the key sections of passenger pigeon genome.

This knowledge has value. Sequences of passenger pigeon genome can be set alongside the genome of a related bird such as the band-tailed pigeon to see where the main differences lie. A genome editing technique called CRISPR has recently become available to cut genomes in precisely targeted places and to replace the extracted DNA with a sequence of the scientist’s choice. In principle, you could find the defining parts of the band-tail pigeon genome and replace them with manufactured stretches of passenger pigeon genome.

At around a billion base pairs for a complete passenger pigeon genome, this transformation would be time-consuming work. Even when the band-tailed genome has been edited so that it looks mostly like a passenger pigeon genome, the challenges are not yet over. Unlike mammals, a bird genome cannot be stuffed into an ovum, stimulated with a small electric shock, cultured for a few rounds of cell divisions, and then implanted into a receptive womb.  For one thing, birds don’t have wombs. They have oviducts. In birds, embryo development takes place in a yolk inside a hard-shelled egg that is constantly in motion. The solution Revive and Restore is pursuing is to edit male and female sex cells of the band-tailed pigeon to turn them into passenger pigeon sex cells. These edited cells will be placed into male and female band-tailed pigeons where they will ready themselves in each bird’s gonads. When two of these doctored birds breed, the union of edited sperm and edited ovum will result in an embryo with a passenger pigeon genome.

If all goes according to plan, after about three weeks of incubation, the two doting band-tailed pigeon parents are going to be absolutely astonished to see their pure white egg crack open and a passenger pigeon emerge into the light of day.

Although the technology is not yet ready for showtime, it is getting close enough that ethicists are starting to pay attention. I have discussed some of the ethical quandaries raised by de-extinction here and here. One of the issues often raised involves animal welfare. In all this editing and gene splicing, our knowledge may not be as good as we think. Errors are almost certain leading to numerous failed hatches and deformed newborns. Is this fair to either the parents or the chicks? Maybe you don’t care enough about pigeons to worry about this but scientists are also trying to de-extinct a woolly mammoth using Indian elephant parents. Elephants are smart, social, and clearly feel both pain and grief. Is such experimentation justifiable?

Another question concerns the environment into which the de-extincted pigeons would be released.  Hasn’t life moved on and new species filled the void left after the nineteenth century slaughter? Can we be sure that placing a species back into an environment from which it has been absent for a century won’t wreak a new kind of ecological havoc? And, as we contemplate that worry, can we really be confident that we would be introducing an authentic passenger pigeon? The foundation of its genome would be band-tailed pigeon and its parents would possess neither the same genes nor the same behaviors as real passenger pigeon parents. Perhaps the expensive newborn is only a weird sort of hybrid.

The numerous ethical issues that come into play make what is sometimes called “resurrection biology” into an ethical minefield. But behind all of these questions lurks an even bigger one.

Before embarking on such a technology we might ask ourselves how much control our species is entitled to assume of the world around us? Certainly, we already exert a lot of influence on the earth. We mine it, we plough it, we pave it with cement, we heat it up, and we dam its mighty rivers. We transform it in innumerable ways to serve our purposes.

But taking up the technology of de-extinction ensures a future involving transformations unlike any others. We will for the first time be able to choose who lives, who dies, and even who stays dead forever.

As one enthusiast for de-extinction has claimed “We are as Gods and might as well get good at it.”

Is this really our proper role?

Image by Cotinis