16: Extinction - Biology

16: Extinction - Biology

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Table (PageIndex{1}) Major Extinction Events
EraPeriodEpochApproximate Duration of Era, Period or Epoch (millions of years before present)Major Extinction Evens
CENOZOICQuaternaryHolocenepresent - 0.01

(6^{th}) major extinction ?

(5^{th}) major extinction (end of Cretaceous; K-T boundary)

(4^{th}) major extinction (end of Triassic)

(3^{th}) major extinction (end of Permian)

(2^{nd}) major extinction (Late Devonian)

(1^{st}) major extinction (end of Ordovician)




(Carboniferous) Pennsylvanian

(Carboniferous) Mississippian325-360

Each of the first five mass extinctions shown in Table (PageIndex{1}) represents a significant loss of biodiversity - but recovery has been good on a geologic time scale. Mass extinctions are apparently followed by a sudden burst of evolutionary diversification on the part of the remaining species, presumably because the surviving species started using habitats and resources that were previously "occupied" by more competitively successful species that went extinct. However, this does not mean that the recoveries from mass extinction have been rapid; they have usually required some tens of millions of years (Jablonski, 1995).

It is hypothesized that we are currently on the brink of a "sixth mass extinction," but one that differs from previous events. The five other mass extinctions predated humans and were probably the ultimate products of some physical process (e.g. climate change through meteor impacts), rather than the direct consequence of the action of some other species. In contrast, the sixth mass extinction is the product of human activity over the last several hundred, or even several thousand years. These mass extinctions, and their historic and modern consequences are discussed in more detail in the modules on Historical perspectives on extinction and the current biodiversity crisis, and Ecological consequences of extinctions..


a species is assumed to be extinct when there is no reasonable doubt that the last individual has died (IUCN, 2002)
the complete disappearance of a species from Earth
Mass extinction
a period when there is a sudden increase in the rate of extinction, such that the rate at least doubles, and the extinctions include representatives from many different taxonomic groups of plants and animals

Stanford biologist warns of early stages of Earth's 6th mass extinction event

Stanford Biology Professor Rodolfo Dirzo and his colleagues warn that this "defaunation" could have harmful downstream effects on human health.

Elephants and other large animals face an increased risk of extinction in what Stanford Biology Professor Rodolfo Dirzo terms "defaunation."

The planet's current biodiversity, the product of 3.5 billion years of evolutionary trial and error, is the highest in the history of life. But it may be reaching a tipping point.

In a new review of scientific literature and analysis of data published in Science, an international team of scientists cautions that the loss and decline of animals is contributing to what appears to be the early days of the planet's sixth mass biological extinction event.

Since 1500, more than 320 terrestrial vertebrates have become extinct. Populations of the remaining species show a 25 percent average decline in abundance. The situation is similarly dire for invertebrate animal life.

And while previous extinctions have been driven by natural planetary transformations or catastrophic asteroid strikes, the current die-off can be associated to human activity, a situation that the lead author Rodolfo Dirzo, a professor of biology at Stanford, designates an era of "Anthropocene defaunation."

Across vertebrates, 16 to 33 percent of all species are estimated to be globally threatened or endangered. Large animals – described as megafauna and including elephants, rhinoceroses, polar bears and countless other species worldwide – face the highest rate of decline, a trend that matches previous extinction events.

Larger animals tend to have lower population growth rates and produce fewer offspring. They need larger habitat areas to maintain viable populations. Their size and meat mass make them easier and more attractive hunting targets for humans.

Although these species represent a relatively low percentage of the animals at risk, their loss would have trickle-down effects that could shake the stability of other species and, in some cases, even human health.

For instance, previous experiments conducted in Kenya have isolated patches of land from megafauna such as zebras, giraffes and elephants, and observed how an ecosystem reacts to the removal of its largest species. Rather quickly, these areas become overwhelmed with rodents. Grass and shrubs increase and the rate of soil compaction decreases. Seeds and shelter become more easily available, and the risk of predation drops.

Consequently, the number of rodents doubles – and so does the abundance of the disease-carrying ectoparasites that they harbor.

"Where human density is high, you get high rates of defaunation, high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission," said Dirzo, who is also a senior fellow at the Stanford Woods Institute for the Environment. "Who would have thought that just defaunation would have all these dramatic consequences? But it can be a vicious circle."

The scientists also detailed a troubling trend in invertebrate defaunation. Human population has doubled in the past 35 years in the same period, the number of invertebrate animals – such as beetles, butterflies, spiders and worms – has decreased by 45 percent.

As with larger animals, the loss is driven primarily by loss of habitat and global climate disruption, and could have trickle-up effects in our everyday lives.

For instance, insects pollinate roughly 75 percent of the world's food crops, an estimated 10 percent of the economic value of the world's food supply. Insects also play a critical role in nutrient cycling and decomposing organic materials, which helps ensure ecosystem productivity. In the United States alone, the value of pest control by native predators is estimated at $4.5 billion annually.

Dirzo said that the solutions are complicated. Immediately reducing rates of habitat change and overexploitation would help, but these approaches need to be tailored to individual regions and situations. He said he hopes that raising awareness of the ongoing mass extinction – and not just of large, charismatic species – and its associated consequences will help spur change.

"We tend to think about extinction as loss of a species from the face of Earth, and that's very important, but there's a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well," Dirzo said. "Ironically, we have long considered that defaunation is a cryptic phenomenon, but I think we will end up with a situation that is non-cryptic because of the increasingly obvious consequences to the planet and to human wellbeing."

AQA Trilogy Biology Unit 7 Lesson 16 Extinction or Survival

Lesson 16 of a complete unit of work for the new GCSE Biology Unit 7. Each lesson contains full objectives and challenge throughout.


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The population extinction pulse we describe here shows, from a quantitative viewpoint, that Earth’s sixth mass extinction is more severe than perceived when looking exclusively at species extinctions. Therefore, humanity needs to address anthropogenic population extirpation and decimation immediately. That conclusion is based on analyses of the numbers and degrees of range contraction (indicative of population shrinkage and/or population extinctions according to the International Union for Conservation of Nature) using a sample of 27,600 vertebrate species, and on a more detailed analysis documenting the population extinctions between 1900 and 2015 in 177 mammal species. We find that the rate of population loss in terrestrial vertebrates is extremely high—even in “species of low concern.” In our sample, comprising nearly half of known vertebrate species, 32% (8,851/27,600) are decreasing that is, they have decreased in population size and range. In the 177 mammals for which we have detailed data, all have lost 30% or more of their geographic ranges and more than 40% of the species have experienced severe population declines (>80% range shrinkage). Our data indicate that beyond global species extinctions Earth is experiencing a huge episode of population declines and extirpations, which will have negative cascading consequences on ecosystem functioning and services vital to sustaining civilization. We describe this as a “biological annihilation” to highlight the current magnitude of Earth’s ongoing sixth major extinction event.

The loss of biological diversity is one of the most severe human-caused global environmental problems. Hundreds of species and myriad populations are being driven to extinction every year (1 ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ –8). From the perspective of geological time, Earth’s richest biota ever is already well into a sixth mass extinction episode (9 ⇓ ⇓ ⇓ ⇓ –14). Mass extinction episodes detected in the fossil record have been measured in terms of rates of global extinctions of species or higher taxa (e.g., ref. 9). For example, conservatively almost 200 species of vertebrates have gone extinct in the last 100 y. These represent the loss of about 2 species per year. Few realize, however, that if subjected to the estimated “background” or “normal” extinction rate prevailing in the last 2 million years, the 200 vertebrate species losses would have taken not a century, but up to 10,000 y to disappear, depending on the animal group analyzed (11). Considering the marine realm, specifically, only 15 animal species have been recorded as globally extinct (15), likely an underestimate, given the difficulty of accurately recording marine extinctions. Regarding global extinction of invertebrates, available information is limited and largely focused on threat level. For example, it is estimated that 42% of 3,623 terrestrial invertebrate species, and 25% of 1,306 species of marine invertebrates assessed on the International Union for Conservation of Nature (IUCN) Red List are classified as threatened with extinction (16). However, from the perspective of a human lifetime it is difficult to appreciate the current magnitude of species extinctions. A rate of two vertebrate species extinctions per year does not generate enough public concern, especially because many of those species were obscure and had limited ranges, such as the Catarina pupfish (Megupsilon aporus, extinct in 2014), a tiny fish from Mexico, or the Christmas Island pipistrelle (Pipistrellus murrayi, extinct in 2009), a bat that vanished from its namesake volcanic remnant.

Species extinctions are obviously very important in the long run, because such losses are irreversible and may have profound effects ranging from the depletion of Earth’s inspirational and esthetic resources to deterioration of ecosystem function and services (e.g., refs. 17 ⇓ ⇓ –20). The strong focus among scientists on species extinctions, however, conveys a common impression that Earth’s biota is not dramatically threatened, or is just slowly entering an episode of major biodiversity loss that need not generate deep concern now (e.g., ref. 21, but see also refs. 9, 11, 22). Thus, there might be sufficient time to address the decay of biodiversity later, or to develop technologies for “deextinction”—the possibility of the latter being an especially dangerous misimpression (see ref. 23). Specifically, this approach has led to the neglect of two critical aspects of the present extinction episode: (i) the disappearance of populations, which essentially always precedes species extinctions, and (ii) the rapid decrease in numbers of individuals within some of the remaining populations. A detailed analysis of the loss of individuals and populations makes the problem much clearer and more worrisome, and highlights a whole set of parameters that are increasingly critical in considering the Anthropocene’s biological extinction crisis.

In the last few decades, habitat loss, overexploitation, invasive organisms, pollution, toxification, and more recently climate disruption, as well as the interactions among these factors, have led to the catastrophic declines in both the numbers and sizes of populations of both common and rare vertebrate species (24 ⇓ ⇓ ⇓ –28). For example, several species of mammals that were relatively safe one or two decades ago are now endangered. In 2016, there were only 7,000 cheetahs in existence (29) and less than 5,000 Borneo and Sumatran orangutans (Pongo pygmaeus and P. abelli, respectively) (28). Populations of African lion (Panthera leo) dropped 43% since 1993 (30), pangolin (Manis spp.) populations have been decimated (31), and populations of giraffes dropped from around 115,000 individuals thought to be conspecific in 1985, to around 97,000 representing what is now recognized to be four species (Giraffa giraffa, G. tippelskirchi, G. reticulata, and G. camelopardalis) in 2015 (32).


Metapopulation-type models are used to predict extinction thresholds. The classic metapopulation model is the Levins Model, which is the model of metapopulation dynamics established by Richard Levins in the 1960s. It was used to evaluate patch occupancy in a large network of patches. This model was extended in the 1980s by Russell Lande to include habitat occupancy. [1] This mathematical model is used to infer the extinction values and important population densities. These mathematical models are primarily used to study extinction thresholds because of the difficulty in understanding extinction processes through empirical methods and the current lack of research on this subject. [6] When determining an extinction threshold there are two types of models that can be used: deterministic and stochastic metapopulation models.

Deterministic Edit

Deterministic metapopulation models assume that there are an infinite number of habitat patches available and predict that the metapopulation will go extinct only if the threshold is not met. [1]

Where p= occupied patches, e= extinction rate, c= colonization rate, and h= amount of habitat.

A species will persist only if h> δ

δ= species parameter, or how successful a species is in colonizing a patch. [1]

Stochastic Edit

Stochastic metapopulation models take into account stochasticity, which is the non-deterministic or random processes in nature. With this approach a metapopulation may be above the threshold if determined that it is unlikely it will go extinct within a certain time period. [1]

The complex nature of these models can result in a small metapopulation that is considered to be above the deterministic extinction threshold, but in reality has a high risk of extinction . [1]

When using metapopulation-type models to predict extinction thresholds there are a number of factors that can affect the results of a model. First, including more complicated models, rather than relying solely on the Levins model produces different dynamics. For example, in an article published in 2004, Otso Ovaskainen and Ilkka Hanski explained with an empirical example that when factors such as Allee effect or Rescue effect were included in modeling the extinction threshold, there were unexpected extinctions in a high number of species. A more complex model came up with different results, and in practicing conservation biology this can add more confusion to efforts to save a species from the extinction threshold. Transient dynamics, which are effects on the extinction threshold because of instability in either the metapopulation or environmental conditions, is also a large player in modeling results. Landscapes that have recently endured habitat loss and fragmentation may be less able to sustain a metapopulation than previously understood without considering transient dynamics. Finally, environmental stochasticity, which may be spatially correlated, can lead to amplified regional stochastic fluctuations and therefore greatly affect the extinction risk. [1]

Next steps

What happens after an extinct genome is resurrected is less clear. For mammoths, Asian elephants may be a suitable maternal host, but cloning by nuclear transfer has not yet been achieved for elephants [12]. For other species, cloning is less likely to be successful. If the closest living species is evolutionarily distant or considerably different in size from the candidate species for de-extinction, incompatibilities between the developing embryo and the surrogate mother may mean that alternative technologies, for example artificial wombs (ectogenesis), will need to be developed. Some species, including birds, cannot be cloned by nuclear transfer [13] and other methods, such as germ-line engineering, will have to be used for these species. After birth, these organisms will be reared in captive environments, which will require knowledge of each species’ welfare needs. Captive breeding may also have lasting consequences for behavior and physiology, which may affect the organism’s survival after release into the wild. As genome-engineering technologies advance to the stage where the first phase of de-extinction — birth — is feasible, the second stage — release into the wild — will be enabled by ongoing work in conservation biology that aims to minimize the potentially negative consequences of captive breeding.

Organisms are, of course, more than just the sum of the nucleotides that make up their genome sequences. Embryos that are derived from engineered cells will be exposed to the developmental environment of a different species. Newborns will be raised in social groups that are necessarily different from those of their own species. They will be introduced to different habitats, will consume different diets, and will establish different microbiomes. All of these factors will influence phenotype, and these effects are likely to vary among species and environments. In summary, genome editing may someday create an organism whose genome sequence very closely matches that of an extinct species, but the organism that develops from those edited cells will not be the same as the organism that went extinct.

Rewinding the process of mammalian extinction

With only three living individuals left on this planet, the northern white rhinoceros (Ceratotherium simum cottoni) could be considered doomed for extinction. It might still be possible, however, to rescue the (sub)species by combining novel stem cell and assisted reproductive technologies. To discuss the various practical options available to us, we convened a multidisciplinary meeting under the name "Conservation by Cellular Technologies." The outcome of this meeting and the proposed road map that, if successfully implemented, would ultimately lead to a self-sustaining population of an extremely endangered species are outlined here. The ideas discussed here, while centered on the northern white rhinoceros, are equally applicable, after proper adjustments, to other mammals on the brink of extinction. Through implementation of these ideas we hope to establish the foundation for reversal of some of the effects of what has been termed the sixth mass extinction event in the history of Earth, and the first anthropogenic one. Zoo Biol. 35:280-292, 2016. © 2016 The Authors. Zoo Biology published by Wiley Periodicals, Inc.

Keywords: assisted reproductive technologies (ART) biodiversity conservation endangered species gametes induced pluripotent stem cells (iPSCs) public awareness rhinoceros.

Data gaps and opportunities for comparative and conservation biology

Biodiversity loss is a major challenge. Over the past century, the average rate of vertebrate extinction has been about 100-fold higher than the estimated background rate and population declines continue to increase globally. Birth and death rates determine the pace of population increase or decline, thus driving the expansion or extinction of a species. Design of species conservation policies hence depends on demographic data (e.g., for extinction risk assessments or estimation of harvesting quotas). However, an overview of the accessible data, even for better known taxa, is lacking. Here, we present the Demographic Species Knowledge Index, which classifies the available information for 32,144 (97%) of extant described mammals, birds, reptiles, and amphibians. We show that only 1.3% of the tetrapod species have comprehensive information on birth and death rates. We found no demographic measures, not even crude ones such as maximum life span or typical litter/clutch size, for 65% of threatened tetrapods. More field studies are needed however, some progress can be made by digitalizing existing knowledge, by imputing data from related species with similar life histories, and by using information from captive populations. We show that data from zoos and aquariums in the Species360 network can significantly improve knowledge for an almost eightfold gain. Assessing the landscape of limited demographic knowledge is essential to prioritize ways to fill data gaps. Such information is urgently needed to implement management strategies to conserve at-risk taxa and to discover new unifying concepts and evolutionary relationships across thousands of tetrapod species.

Keywords: Demographic Species Knowledge Index biodemography extinction fertility mortality.

Copyright © 2019 the Author(s). Published by PNAS.

Conflict of interest statement

The authors declare no conflict of interest.


Landscape of demographic knowledge for…

Landscape of demographic knowledge for tetrapods. ( A ) Reptilia. ( B )…

Simplified version of the landscape…

Simplified version of the landscape shown in Fig. 1. ( A ) Reptilia.…

Reported origin of the information…

Reported origin of the information across the 22 data repositories analyzed. Diagrams show…

Climate Change

Climate change , and specifically the anthropogenic (meaning, caused by humans) warming trend presently escalating, is a major extinction threat, particularly when combined with other threats such as habitat loss and the expansion of disease organisms. While scientists disagree about the likely magnitude of the effects, with extinction rate estimates ranging from 15 percent to 40 percent of species destined for extinction by 2050. Scientists agree that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them, in particular, the endemic species. The warming trend will shift colder climates toward the north and south poles, forcing species to move with their adapted climate norms while facing habitat gaps along the way. The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is the new range overlap between polar bears and grizzly bears (Figure 47.15). There are documented cases of these two species mating and producing viable offspring. Changing climates also throw off species’ delicate timed adaptations to seasonal food resources and breeding times. Many contemporary mismatches to shifts in resource availability and timing have already been documented.

Figure 47.15 Since 2008, grizzly bears (Ursus arctos horribilis) have been spotted farther north than their historic range, a possible consequence of climate change. As a result, grizzly bear habitat now overlaps polar bear (Ursus maritimus) habitat. The two species of bears, which are capable of mating and producing viable offspring, are considered separate “ecological” species because historically they lived in different habitats and never met. However, in 2006 a hunter shot a wild grizzly-polar bear hybrid known as a grolar bear, the first wild hybrid ever found. (Image credit: OpenStax Biology 2e)

Range shifts are already being observed: for example, some European bird species ranges have moved 91 km northward. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, and mammals.

Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The accelerating rate of warming in the arctic significantly reduces snowfall and the formation of sea ice. Without the ice, species like polar bears cannot successfully hunt seals, which are their only reliable source of food. Sea ice coverage has been decreasing since observations began in the mid-twentieth century, and the rate of decline observed in recent years is far greater than previously predicted.

Finally, global warming will raise ocean levels due to meltwater from glaciers and the greater volume of warmer water. Shorelines will be inundated, reducing island size, which will have an effect on some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains—a cycle that has provided freshwater to environments for centuries—will also be jeopardized. This could result in an overabundance of salt water and a shortage of fresh water.

Decades of globally coordinated work in conservation have failed to slow the loss of biodiversity. To do better—even if that means nothing more than failing less spectacularly—bolder thinking is necessary. One of the first possible conservation applications of synthetic biology to be debated is the use of genetic tools to resurrect once-extinct species. Since the currency of conservation is biodiversity and the discipline of conservation biology was formed around the prevention of species extinctions, the prospect of reversing extinctions might have been expected to generate unreserved enthusiasm. But it was not universal acclaim that greeted the coming-out party for “de-extinction” that was the TEDx conference and accompanying National Geographic feature in 2013. Why the concern, the skepticism, even the hostility among many conservationists about the idea of restoring lost species? And how does this professional concern relate to public perception and support for conservation? This essay explores the barriers to the acceptance of risky new genomic-based conservation tools by considering five key areas and associated questions that could be addressed in relation to any new conservation tool. I illustrate these using the specific example of de-extinction, and in doing so, I consider whether de-extinction would necessarily be the best first point of engagement between conservation biology and synthetic biology.

Decades of globally coordinated work in conservation have failed to slow the loss of biodiversity. To do better—even if that means nothing more than failing less spectacularly—bolder thinking is necessary. Among the strategies we should consider is engagement with the rapidly expanding field of synthetic biology, whose genetic editing tools suggest new techniques for protecting threatened species and limiting invasive ones, addressing what are currently intractable challenges in conservation. But far from embracing synthetic biology, many in the professional conservation community have responded with what ranges from disinterest to implacable opposition. There is some cautious optimism, but it is hard to find. The louder voices call for resistance. This statement from a civil society group on the prospect of using synthetic biology to address species threats stands out: “[I]n our view, recent proposals to move ahead with real world gene drive trials (e.g., the Genetic Biocontrol of Invasive Rodents project … and the gene drive mosquito in Hawaii) are reckless and irresponsible and do not reflect the essential values of the conservation movement. Such projects should not be funded or promoted.” 1

One of the first possible conservation applications of synthetic biology to be discussed and debated is the use of genetic tools to resurrect once extinct species, an application that has been given the name “de-extinction.” Since the currency of conservation is biodiversity and the discipline of conservation biology was formed around the prevention of species extinctions—prompting some in the field to call it a “crisis discipline”—the prospect of reversing extinctions might have been expected to generate unreserved enthusiasm—a chance to do more than just slow the rate of biodiversity loss, instead, to actually reverse it. But it was not universal acclaim that greeted the coming-out party for de-extinction that was the TEDx conference and accompanying National Geographic feature in 2013. 2 Why the concern, the skepticism, even the hostility among many conservationists about the idea of restoring lost species? And how does this professional concern relate to public perception and support for conservation?

In this essay, I will explore the barriers to the acceptance of risky new genomic-based conservation tools by considering five key areas and associated questions that could be addressed in relation to any new conservation tool. I illustrate these using the specific example of de-extinction, and in doing so, I consider whether de-extinction would necessarily be the best first point of engagement between conservation biology and synthetic biology.

Technological limitations: does the new tool deliver what it promises? “De-extinction” is a compelling and engaging term, seemingly promising that we can reverse irreversible loss. But can we? What exactly might be the resulting product from each of the three currently known de-extinction pathways of backbreeding, cloning, and genomic engineering?

Backbreeding, the artificial selection of domestic animals to produce a wild-type phenotype, assumes that descendant forms carry the genetic material and hence the potential to express the phenotype of an extinct ancestor. Thus, for example, selective breeding of some carefully chosen domestic breeds of cattle might result in a beast that has the size and coloration of the aurochs (Bos primigenius), from which cattle descended. 3 Clearly, however, while some original genetic sequences might be preserved and expressed, generations of hybridization and multiple selection pressures will limit the degree of genetic similarity between the final form and its aurochs ancestor. The best that might be produced is some phenotypic proxy of an extinct form, although genomic information could be used to better guide the creation of such a proxy.

Cloning seems to have the potential to truly resurrect a lost form, for isn't a clone an exact genetic copy? Well, nearly, but perhaps not in critical ways. While the technique of cloning has come a long way since Dolly the sheep and for some taxa is now relatively efficient and low risk, if you are wanting to use cloning to restore an extinct species, some challenges remain. For a start, doing so would require interspecies cloning: for mammals, for example, you would need an appropriate surrogate host that was a near relative of the extinct species to carry an embryo to term. But even before needing a surrogate host, you need an embryo of the extinct species, and unless you have cryo-preserved gametes (eggs and sperm), you will need a host cell in which to place the genetic material from a suitably preserved somatic (body) cell of your extinct form. So, for a start, without carefully frozen cells taken before extinction, cloning is not an option, restricting cloning as a de-extinction pathway to species that went only very recently and from which cells had already been preserved. Even with the right cells, the need to use a surrogate host means there will be genetic components inherited from the host, there will be epigenetic effects whereby the host environment might turn on or off the activity of some genes, and there will be inevitable postnatal differences from the original extinct species due to learning, the rearing environment, diet, and the resulting microbiome. 4

Without cryo-preserved cells, things get harder but not impossible, thanks to rapid advances in the ability to read and write DNA sequences. The genome of the extinct form must be deciphered from any available tissue, and the older the tissue, the more the DNA within it will have deteriorated, inevitably leaving gaps in the genome. These gaps need to be filled with the best approximation of the extinct sequences, likely from a nearest living relative, which can be used to create modified cell lines by replacing DNA sequences of the extant species with synthesized DNA in the extinct species sequence. Nuclei from such cells could then be used in cloning. Clearly, however, the result is not the resurrection of the extinct form, but the creation of a hybrid form with some expression of hybrid traits.

There is, therefore, arguably no such thing as true de-extinction. Rather, the current de-extinction pathways could usefully seek to produce functional proxies of extinct forms 5 —or phenotypic proxies, from a nonconservation viewpoint. But does this matter? What is the cost, the risk, or the harm of creating a proxy of an extinct species?

Opportunity costs: who pays, and what misses out as a result? Any new tool comes at a cost: the direct financial cost of research and development, the resource cost of implementation, and possibly an opportunity cost—the loss of alternatives when a course of action is taken. A major and oft-repeated concern about de-extinction is that even attempting it will divert scarce conservation funding away from extant species and systems that desperately need help, and it's not as if we are turning the tide of biodiversity loss and can afford to let up on traditional conservation. A counterargument is that conservation funding is not a zero-sum game, because the kinds of people or sources of funding for exciting new technology are not the same as for biodiversity conservation. 6 We do not have to fire a wildlife ranger to obtain the funding for mammoth cloning. The prospect of de-extinction might actually increase conservation-related funding, mightn't it?

But it's not quite that simple. We could consider any de-extinction project as consisting really of two distinct and significant projects: (1) resurrecting suitable numbers of suitably diverse proxies of an extinct species and (2) placing them out into an appropriate environment to establish a new population in order to restore lost biodiversity and ecosystem processes and thus enhance ecosystem resilience. I'm assuming for simplicity's sake that de-extinction can be justified by a conservation benefit, rather than for research, advocacy, or commercial gain, although the first so-called de-extinction projects might well derive from nonconservation objectives, so far as the policies and legislations of any host nation allow. So, the project of creating proxies might well obtain funding from those excited by the promise of new technology, but the project of placing them in the environment seems likely, in large part, to become the responsibility of existing biodiversity managers who are already juggling competing priorities and trying to spread scarce dollars across a growing number of threatened species. It would be naïve to assume that the (re)introduction of a proxy of an extinct species would not carry some cost to extant species, either directly through unanticipated ecological effects after the proxy's release or indirectly by demanding limited conservation resources. 7 No new conservation tool will offer a free lunch—someone must pay, and something will lose out. The hard part of that equation, though, might not be who will pay but, rather, the management of risk and uncertainty and the balancing of possible gains and losses.

Moral hazard: who bears the costs if things go wrong? A moral hazard is a situation in which one party takes actions whose risks would be borne by another party. Any new technology for conservation will carry risks: risk of failure and lost resources, of undesired consequences, and so forth. Much of conservation management is about understanding and managing risk, but in general, day-to-day conservation decisions do not involve moral hazard. New conservation tools that employ synthetic biology would, however, carry significant risks, and they would pose a moral hazard if the decisions to implement them resulted in costs to people not involved in those decisions, including future generations—for example, somehow woolly mammoths lead to a resurgence of some mammoth pathogen that wreaks havoc on Siberian communities (which I regard as quite unlikely, to say the least). In the de-extinction debate, a moral hazard would arise if de-extinction were seen as providing a techno-fix to the crisis of species extinctions and biodiversity loss and that perception undermined societal and political support for efforts to prevent species extinctions. 8

Another hazard would arise if the implementation of a new tool had a deleterious effect that could threaten or reduce extant biodiversity and leave recipient ecosystems more impoverished. For example, the environmental release of a proxy species carries the risk that the introduced form will not perform ecologically as predicted because of key differences compared to the extinct form or because of ecological and environmental changes since extinction. There is a risk that the project will fail, as introduced individuals die, but also a risk of impacts on extant biodiversity through novel interactions, and even a risk that the proxy species will become invasive, threatening both ecological integrity and human livelihoods. To a degree, these are the risks associated with any translocation of species for conservation purposes, particularly assisted colonization (moving a threatened species outside its historic range) and ecological replacements (introducing a new species to fill the ecological role of a lost one). 9 The release of any proxy of an extinct species can be defined as a conservation translocation, 10 and it would be appropriate to apply existing International Union for Conservation of Nature (IUCN) translocation guidelines to those releases. 11 Those guidelines urge consideration of alterative actions and efforts to understand and minimize risks.

Public perceptions: will this garner or reduce public support? Most resurrected forms will, by definition, be genetically modified organisms and subject to national and international legislation. They will also be vulnerable to the “Monsanto effect,” whereby there is suspicion that commercial motivations might override concern for risks to human health and livelihoods and environmental risks. Will a GMO in the form of an extinct species’ proxy be acceptable? Within captivity, probably released into the environment, less likely but possible. There remains public skepticism about commercial GMO products in many parts of the world, as concern grows about the potential for health and environmental risks. Greater acceptance of GMOs in the service of conservation could, however, come with victories, such as the genetic rescue of critically endangered species or species threatened by disease processes. 12 A good example is the development of transgenic American chestnut trees resistant to the pathogenic fungus Cryphonectria parasitica. 13 Will people be worried that the trees carry genes from other plants, such as wheat, grapes, pepper, and the blight-resistant Chinese chestnut? Or will they simply rejoice in the return to good health of North America's eastern forests?

Similarly, while none of the current pathways of de-extinction would result in a facsimile of an extinct species, detailed concerns about epigenetic effects might not mean much to a general public coming face to face with a reasonable phenotypic proxy of some extinct form. A hybrid Asian elephant with mammoth genes expressing hairiness might well be accepted as the re-creation of a mammoth. So, how might that hybrid change public perceptions? Would extinction no longer be forever, in the public mind? This seems to be a very real possibility, especially given the growing disconnect between humans and the natural world, with most people around the globe having become urban dwellers who may have little connection and perhaps less understanding about their natural heritage. Cynically, one might argue that the prospect of de-extinction would at least not make things worse most humans are focused on health, safety, well-being, social justice, and economic security, anyway, rather than on biodiversity conservation. What might really pose problems for conservation are public perceptions of “Jurassic Park scenarios”—of commercial avarice and scientific hubris. Such a response might reinforce antiscience sentiments and force the professional conservation community to allay public fears. But can a bunch of conservationists beat Hollywood when it comes to public perceptions?

Conservation community: will practitioners support and use the new tool? Conservation practitioners and conservation biologists are, in general, conservative and precautionary. Their focus is on preservation and restoration, limiting human impacts, and slowing or halting biodiversity declines. They have been characterized as looking to the past and being risk averse. 13

C. P. Snow's famous 1959 Rede lecture posited the emergence of two cultures, those of science and the humanities, disengaged from and distrusting of each other. As Stefan Collini has paraphrased Snow's thesis, the “profound mutual suspicion and incomprehension in turn has damaging consequences for the prospects of applying technology to the alleviation of the world's problems.” 14 The conservation community's reluctance to engage with potential new tools for conservation, particularly those involving manipulation of genetic material, is analogous to the literary culture's distrust of science. But while there is some mutual incomprehension, the suspicion is not mutual. The incomprehension is because there is little overlap in the two communities’ respective training, fields of practice, and views of the future. 15 But there is no reason to expect synthetic biologists to be opposed to biodiversity conservation it seems more likely that many are, for the most part, simply unaware of the issues. By contrast, because conservation practitioners have a general aversion to risk, in their limited engagement with new genetic-based approaches, they appear to be focusing more on what they assume to be risks of harm to biodiversity. They are little inclined to proactively engage with the proponents of potential new tools and solutions in order to fully understand the likelihood and management of those risks—even though, ironically, the discipline of conservation biology was founded on a mindset of proactive engagement. 16

What is the way forward? Can we engage a skeptical and cautious conservation community, harness the enthusiasm of the public imagination, and ensure that risks are understood and managed? Despite the IUCN's interest in developing guidelines for de-extinction, perhaps the way is not through this early and controversial point of engagement between conservation biology and synthetic biology. Perhaps the way is through cautious application of synthetic biology in applications that are closer to conservation's familiar mode of addressing threats to extant species. These applications might include the reintroduction of lost genetic diversity in critically endangered species that have suffered from historical genetic bottlenecks, the control of wildlife diseases and zoonoses through genetic manipulation of vectors, and the eradication of invasive pests through genetically engineered sterility. 17 Early and demonstrable success in tackling, even in controlled trials, these types of intractable conservation challenges will do much to start a more informed debate about human management and manipulation of the natural world.

Watch the video: Η Εξαφάνιση - S1 - Επεισόδιο 17 (May 2022).