How to Clone a Mammoth

by Shapiro, Beth

  Rearing the young is another challenge that was highlighted by the California condor project. What steps will need to be taken within a de-extinction project to identify or manufacture appropriate social surrogates? How important is rearing within a social group, and what will the effect be if that social group is not entirely natural? Will it be possible for the juveniles to avoid imprinting either to humans or the surrogate species? This is a particularly difficult list of questions, and the answers are likely to vary considerably from species to species. One way to minimize these problems may be to select for de-extinction only species that lack significant parental care, where behavior seems more likely to be genetically hard-wired than it is to be learned. That would be bad news for highly social elephants and not particularly good news for passenger pigeons, which bred in large colonies with up to 100 nests in a single tree and both parents tending to each chick. It does not, however, exclude all species as candidates for de-extinction. Most turtles and tortoises appear to have very little parental care, which has made them target species for a variety of captive-breeding and reintroduction programs. Intriguingly, releases of captive-bred sea turtles have been conducted for decades and have thus far resulted in zero successful establishments or reestablishments of sea turtle–breeding colonies. We simply do not yet understand the complexities of how some behaviors are learned.

  Another issue raised by the condor breeding program concerns the extent to which breeding in captivity alters behavior. California condors raised by puppets, despite their time served in aviary-based mentoring programs, displayed different behavior toward humans than did their siblings that had the fortune of being reared by actual condors. Puppet-reared condors integrated poorly with the rest of the condor community. Rather than shy away from humans, they preferred to play with garbage, hang about on roofs chewing on loose tiles, and stare disdainfully at rock climbers from above. Of course, with California condors, altered behavior was measured by comparison with the behavior of wild-reared animals. What constitutes “natural” behavior for species that have never been observed in the wild?

  Individuals that are raised by surrogate parents or by social groups comprising closely related species can also develop species confusion, where offspring develop behaviors that are more similar to behaviors of the foster-parents’ species than to their own species. If the foster parent is simply an unengineered version of the same species, it may be extremely challenging to establish and maintain behavioral differences using genome editing, and it might become necessary either to manufacture a surrogate social group or to use a more distantly related species. After release, another significant challenge will be to enforce reproductive isolation between engineered and unengineered populations of the same species. If the natural ranges of these groups overlap, uncontrolled breeding may quickly erode any genetic distinction between them.

  Another issue raised by the California condor program concerns the number of individuals that will need to be released in order to establish an effective, natural social structure in the wild. Now that there are more than 230 California condors alive in the wild, it is apparent that condors are social animals whose social structure is key to their survival. California condors mate for life, are highly protective of their mates and territories, and have a strong system of social dominance that determines who eats and when. This social structure did not become apparent to scientists until their population size was sufficiently large to allow it to form. Elephants are also strongly social animals. Females live and raise the young in large, multigenerational family groups. Within these groups, a dominant, older, and wiser matriarch is responsible for decision making, including where to go to find food and water and when to flee from a potential threat. If captive-bred populations are to survive in the wild, the initial release will have to include a sufficiently large number of individuals and a sufficient range in age and experience to allow these social structures to emerge.

  The Allee effect is a biological phenomenon that sometimes acts on very small populations. If a population is subject to an Allee effect, it is only stable when it is larger than a certain threshold size. If the number of individuals dwindles below that size, the population plummets suddenly to extinction. The idea behind the Allee effect is that individuals are more fit when the population is big. When the population is small, individuals are more susceptible to predation, have a harder time finding a mate, and are less efficient at discovering sources of food.

  The extinction of the passenger pigeon in eastern North America is often cited as an example of the Allee effect in action. As hunting pressure increased and passenger pigeon populations declined, individuals may have been easier targets for predators like hawks without the protection of their enormous flocks. Also, deforestation around the turn of the century meant that food in the form of fruiting beech and oak trees was becoming increasingly difficult to find. The smaller populations of passenger pigeons may have been less capable of locating this limiting resource than larger populations would have been. If it is true that passenger pigeons suffered as a consequence of the Allee effect and are only capable of surviving in very large populations, it could be tough to generate a sufficiently large population in captivity for passenger pigeons to ever establish self-sustaining populations in the wild.

  Ultimately, the goal of de-extinction is to create populations that are able to survive in the wild without human intervention. The California condor provides more insight here. Since their reestablishment in the wild, California condors continue to require considerable veterinary care. A main contributor to their decline, at least in the latter half of the twentieth century and continuing to today, has been lead poisoning. The birds eat fragments of lead bullets left behind in carcasses and gut piles, and the lead builds up in their system, making them very sick and eventually killing them. Lead bullets are being phased out of use in California, and the ban should be fully in effect by 2019. For now, however, lead bullets remain in use. Every condor is removed from the wild twice each year and put through extensive veterinary testing. Many of these birds are returned to captivity for treatment, specifically for the removal of lead from their blood. Without this expensive and time-consuming treatment, the birds would die.

  The sad fact is that most species reintroductions fail. Why reintroductions fail is likely to vary from case to case. If whatever it was that drove the species to extinction or near-extinction in the first place was not accurately identified or, as in the case of the condor, has not been adequately resolved, then the reintroduction has little chance of succeeding. Genetic, behavioral, and social anomalies may arise as a consequence of captive breeding, and these may make captive-bred individuals unfit for life in the wild.

  GENETICALLY MODIFIED ORGANISMS AS ENDANGERED SPECIES

  One additional and important consideration in this final phase of de-extinction is how resurrected organisms (or organisms with resurrected traits) will be regulated once they are ready for release. Most countries have laws that regulate the release of non-native species within their borders. These regulations will almost certainly apply to de-extinction projects that involve the genetic engineering of existing species. Elephants whose genomes code for mammoth traits would probably be regulated as invasive species in Siberia, for example. Bucardos, however, might not be considered invasive should they be released into their former range. Instead, the practicalities of bucardo re-release might be determined by public land use laws and perhaps even endangered species laws. There is another option, however. Because the organisms will all have been genetically engineered to some extent, they will fall into the category of genetically modified organisms, or GMOs, and—perhaps—under the purview of GMO legislation.

  The world has widely varying opinions about GMOs, including whether they should be considered safe, how they should be managed, and which laws should apply to their use and distribution. This diversity of opinion is reflected in the scope of laws in place to regulate GMOs. The United States is among
the least stringent countries when it comes to regulating GMOs and is one of the largest producers of GMO crops. The European Union has some of the most stringent GMO regulations in the world, but countries vary considerably within the EU with regard to whether they believe those regulations are necessary or even fair. New Zealand has among the strictest regulations of GMOs. If moa are someday brought back to life, would these rules exclude them from being released into the wild? Or from being eaten by New Zealanders?

  To explore the regulatory labyrinth to be navigated by resurrected organisms, let’s consider the release of passenger pigeons in the northeastern United States. If we succeed in creating band-tailed pigeons whose genomes contain some passenger pigeon DNA—for simplicity, let’s refer to them as passenger pigeons—they will have been produced using genetic engineering technologies, specifically genome editing and cloning via primordial germ cell transfer. They will, from a scientific perspective, be genetically modified organisms. However, they may also be nonnative, they will almost certainly have some effect on the environment into which they are released, and they may even be considered endangered. To which regulatory agency can we turn to determine whether and where we can release them?

  First, let’s consider their status as GMOs. In the United States, a framework was developed in the 1980s to regulate GMOs using existing federal agencies. These agencies were charged with evaluating the safety of and risk associated with specific types of GMOs. Following this framework, GMO-derived food and medicines are regulated by the Food and Drug Administration, while organisms that are characterized as GMO pesticides—for example, plants that have been engineered to express genes that make themselves resistant to viruses—fall within the remit of the Environmental Protection Agency. The risk that these GMOs pose to the environment and to agriculture is evaluated by the Department of Agriculture.

  While this framework seems straightforward, one important limitation stands out: these laws apply only to GMOs that are intended to be consumed. So unless our motivation for passenger pigeon de-extinction was to farm passenger pigeons and sell them to the hungry masses, resurrected passenger pigeons would not be considered GMOs in the United States, at least by federal laws.

  For the purpose of exploration, let’s say we do want to bring back passenger pigeons so that we can sell them as food. In this case, our edible passenger pigeons would be reviewed by the FDA as GMOs. If the FDA review found that GM passenger pigeons contained some sort of unusual substance that was not found in band-tailed pigeons (the unmodified food product), the FDA could then establish mechanisms to oversee their farming and production. FDA laws would not, however, address what might happen should passenger pigeons escape from the farm and take up residence elsewhere.

  At present, GMO regulations in most countries apply only to food. If, after escaping their FDA-regulated farms in the north-eastern United States, our grown-for-food passenger pigeons flew across the Canadian border to reestablish free-living populations across their once-native range, whether they were “allowed” to enter Canada would be determined by whether they were defined as an invasive species, not by their status as GMOs.

  Our intent is, of course, not to farm and sell passenger pigeon meat, but to establish natural populations of passenger pigeons in the wild. While this intent excludes resurrected passenger pigeons from federal regulation as GMOs, it does not exclude them from local GMO regulation. In the United States, local GMO regulations can be much more inclusive in their definition of GMOs, and many local laws ban GMOs even when they are not meant to be used as food. In Marin County, California, for example, an ordinance is in place that bans all GMOs except those that are used in enclosed, licensed, medical facilities. The ordinance defines GMOs as “an organism or the offspring of an organism, the DNA of which has been altered or amended through genetic engineering.” That definition would seem to exclude resurrected passenger pigeons from moving to Marin, even though this is where Stewart Brand and Ryan Phelan live, and where Revive & Restore—the organization that is behind their de-extinction—is based.

  In most countries, resurrected species will be regulated under environmental statutes—invasive species, public land use, and endangered species laws—rather than under GMO laws. It is relatively easy to understand why the first two categories apply: most (but not all) resurrected species will be nonnative, and many release programs will include public land. However, is it appropriate for resurrected species (or species with resurrected traits) to be protected as endangered species?

  Endangered species protection for resurrected species sounds good, but it would likely be a double-edged sword. Increased regulation would make it harder for breeding facilities and wildlife managers to manipulate the species, even if such manipulation were designed to benefit their recovery. At the same time, protection would provide a variety of benefits. For example, in the United States, it is illegal to kill individuals belonging to a protected species without an explicit permit. In addition, other federal agencies have to explicitly consider how their decisions or regulations would impact protected species. Critical habitat for the species also has to be identified and protected, and officially sanctioned plans have to be developed to recover their populations.

  For the passenger pigeon to receive protection under the US Endangered Species Act, it would first have to be listed as an endangered species by the US Fish and Wildlife Service. Species qualify for listing if they are affected by one or more of five factors: (1) real or imminent habitat loss; (2) overexploitation; (3) disease or predation; (4) inadequate protection by other regulatory mechanisms; and (5) other natural or manmade attributes that will affect its continued existence. Without a good idea of what its range might be, it is hard to know whether the passenger pigeon would qualify for listing on the grounds of having insufficient habitat. Given that regulations governing GMOs are not meant to protect the status of the GMOs (but instead to protect the world from GMOs), it would almost certainly qualify on the grounds of factor 4: insufficient protection. Passenger pigeons would probably lack genetic diversity, which would be a factor (manmade, in this instance) that could affect its continued existence (factor 5). Also, back-breeding with band-tailed pigeons could lead to the re-extinction of the passenger pigeon, and therefore band-tailed pigeons might be considered natural factors that also could affect their continued existence (factor 5).

  So, the passenger pigeon would probably qualify for listing within the United States as endangered, but what about as a species? This is trickier. Does a band-tailed pigeon with a bit of passenger pigeon DNA inserted into its genome constitute a separate species? The Endangered Species Act does not wade into the murky waters of defining a biological species but instead considers any subspecies or even (for vertebrates) “distinct population segments” as separate species, for the purpose of listing. Because resurrected passenger pigeons would really be band-tailed pigeons with a few or more extinct genes thrown in, this—as a distinct population segment of band-tailed pigeons—is the most likely avenue by which they might qualify for listing.

  In the unfeeling eyes of the law at least, passenger pigeons probably would qualify for protection as endangered species in the United States. Does protection by this mechanism make sense, however, in light of the purpose of the legislation? The Endangered Species Act and similar regulations were intended to protect living endangered species. Just as many food and drug laws were not developed with GMOs in mind, endangered species legislation was not developed with de-extinction in mind. Forcing existing regulations to absorb unextinct species, with their myriad additional challenges and uncertainties, could cause these often precariously balanced sets of rules and regulations to come tumbling down, with potentially dire consequences to the existing legal structure and to those species that are currently under protection.

  Clearly, regulations to protect endangered species were not envisioned to protect man-made species. But is a species that contains resurrected traits truly man-made? It might have an al
tered genome sequence, but the alterations evolved, naturally, within the genomes of now-extinct species. The traits themselves are natural, but the genetic combination of these traits and the genome of a living species is man-made. This semantic limitation—the necessity of distinguishing completely between natural and unnatural—is a limitation of existing environmental laws that illustrates how unprepared the regulatory sphere is for de-extinction.

  The International Union for the Conservation of Nature currently lists the band-tailed pigeon as a “species of least concern.” This is good news for the first phase of passenger pigeon de-extinction, as it limits what regulations govern the use of band-tailed pigeons in genetic-engineering and captive-breeding programs. But it’s less good news for the last phase of de-extinction. If the band-tailed pigeon were itself endangered, then the Endangered Species Act would have a convenient mechanism to provide the passenger pigeon with the benefits of protection but without the bureaucracy. To provide some flexibility for captive-breeding programs of endangered species, the Endangered Species Acts allows experimental populations of endangered species to be considered “nonessential,” in that the survival of that particular population is not absolutely necessary for the survival of the species. Nonessential populations must live in a geographic area that is completely separate from the essential part of the species range. Conveniently, living separately from other populations of band-tailed pigeons will also be important for ensuring the survival of passenger pigeons genes within band-tailed pigeon genomes.