Forever or not?

Could we, and should we, bring back extinct species? (13 minute read)

When I walk in the forest, I notice what isn’t there as much as I notice what is. In the little reserve where I’m helping with restoration, I notice that there are few mature trees, because it’s an area where the forest was almost completely cleared. In Khandallah Park, there are large trees forming a canopy, but certain species are missing, such as rīmū, because large, valuable timber trees were logged before the park was protected. In Ōtari/ Wilton’s Bush, there are some ancient, giant trees, including an 800-year-old rīmū, but only a few species of bird. In Zealandia, the birdlife is like no other forest in Wellington, but the plant life is still centuries away from being as good as Ōtari or Khandallah Park.

In none of these forests, though, do I hear the sharp, whistling cry of the piopio, the trills, rasps and seeps of the mātuhituhi, or the doleful shrieks of the whēkau or laughing owl. I’ve never turned my head towards a rustling and crashing in the bushes and seen a moa. I’ve never seen a flash of white-tipped tail feathers and wondered if it could be a huia.

I don’t often notice these absences, because all of these birds were gone before I was born. But I do wonder about them. I wonder how different our forests would have been with large birds moving through the undergrowth, browsing on twigs and leaves in an entirely different way from deer, goats and possums. I wonder how the distribution of plants would change with more large birds to eat and disperse their fruit. I wonder what our forests would sound like with all the missing birdcalls.

I’m haunted by the recording, made in the late 1940s, of Hēnare Hāmana whistling huia calls he’d not heard since childhood. Hēnare had been part of an expedition to find the birds in 1909. The expedition hoped to find a pair which could be moved to an island such as Te-Hauturu-o-Toi (Little Barrier). Hēnare did succeed in calling one bird, a male. I imagine that bird, alone in the forest, hearing the familiar call but, when it approached, seeing only humans.

Image credit: Melanie Newfield

In less than 1000 years, New Zealand has lost around half of its land vertebrates, 59 birds, three reptiles, three frogs and one bat. It’s a catastrophic loss, not only because the species themselves have gone, but because they were once part of a complex network of interactions, an ecosystem, which is altered beyond recognition by their absence. The extinction of one species can trigger further losses too. The huia, for example, had a tiny parasite which lived on its skin. Since it lived on no other bird, it disappeared along with its host. Perhaps such a parasite doesn’t seem like a great loss, but we must have lost countless such species without ever knowing.

While we can debate the impact of losing tiny parasites, the extinction of some species has had clear effects on whole ecosystems. The Mascarene Islands – Mauritius, Rodrigues and Reunion, volcanic islands in the Indian Ocean – once had five species of giant tortoise, as well as that icon of extinction, the dodo. All are now extinct. As a result, large-seeded species with fleshy fruits, which would have been eaten by tortoises, dodos and other large fruit-eating animals, are now suffering a lack of dispersal. Low-growing plants are threatened by the dense growth of larger species, both native and introduced, which dominate without tortoises to graze on them. On the island of Guam, birds, bats and lizards were important pollinators and seed dispersers for native trees. The introduction of the brown tree snake has driven many of these native animals to extinction. As a result, the island’s native trees are either producing fewer seeds, due to lack of pollination, or the seeds are not being dispersed. Although it’s not clear whether there have been similar impacts from New Zealand extinctions, there is evidence that the reduction in bird numbers and regional extinctions of birds such as hihi and korimako has affected some plants.

We have made remarkable progress in bringing some species back from the brink, but extinction has long seemed final. This understanding has seeped into common knowledge, in phrases like dead as a dodo and the kua ngaro i te ngaro o te moa (lost as the moa was lost). But as gene technology has advanced, the possibility of de-extinction has become more widely discussed. We are closer than ever to being able to bring a species back. But what would it really take to revive a species such as the huia or one of the nine species of moa? And even if we could, should we?

The earliest attempts to revive an extinct species date back to the 1920s. Two German zoo directors attempted to recreate the wild cattle of Europe, known as the aurochs, by cross-breeding domestic cattle with similar traits. They did the same with horses, attempting to revive an ancient breed of horse known as the tarpan, which had died out only a few decades earlier. They did breed cattle and horses which were more wild in appearance and nature, although the cattle didn’t really resemble the aurochs. At the time, some of the cattle were released into the Białowieża forest in Poland, where they were hunted by high-ranking Nazi officials, including Hermann Göring.

These cattle, as well as hardy breeds of horse, have been used since the 1980s in projects to restore some ecosystems in Europe, as a substitute for a range of large herbivores which are now extinct. They have also been used for further breeding. However, this can’t really be considered any kind of de-extinction. Breeders have been mostly aiming to reproduce an appearance. It’s really an example of what scientists refer to an analogue species, which is a related species brought in to replace the role of an extinct species in a particular environment. This is the approach Mauritius using. After some careful experiments, they have introduced tortoises from Aldabra atoll (a remote island in the Seychelles) to some of their protected areas.

Since European domestic cattle were descendants of the aurochs, bringing back the extinct ancestor from selective breeding wasn’t an unreasonable approach. But to truly bring back an extinct species requires more than just selective breeding to create something which looks similar. It requires the DNA of the extinct species.

But how do we get from DNA to a live animal¹? First, the DNA needs to be in a living cell, otherwise it’s just a molecule. In a few cases, scientists have been able to recover whole cells from extinct species and clone them, which makes the prospect of reviving that species easier. Easier, but certainly not easy.

This has already been attempted, with a kind of wild goat from Spain. In 1999, there was only one of these goats remaining, and scientists collected and cultured skin cells from it before it died. But it’s no simple matter to grow a new goat from skin cells. So, they took eggs from domestic goats, removed the nucleus, which is the part which holds the DNA, and then injected a single cultured skin cell into the coating for the domestic goat’s egg. They then fused the two cells together with an extremely short pulse of electricity and induced the resulting egg cell to divide and form an embryo using a series of different chemicals. Finally, they transferred the embryos to a related wild goat, or to wild/domestic goat hybrids.

They managed to create hundreds of reconstructed eggs, and transferred dozens into live goats. Only a small proportion of the transfers resulted in a pregnancy, and from those, only one live wild goat was born, and it lived for only a few minutes.

If cloning worked, it could, theoretically, serve as a backup plan for highly endangered species, just in case more conventional conservation efforts failed. The problem is that, so far, it barely works. The first cloned mammal, Dolly the sheep, was born in 1996, but we are still struggling to clone mammals effectively. The process is extremely inefficient – it still takes many attempts to produce a live animal. The animals which are born often have health problems and age prematurely, because although their bodies are young, their chromosomes (the structures which hold their DNA), are not. And we still can’t clone birds.

What if we don’t have whole cells? If we want to bring back the huia, or the moa, or even the more recently extinct tutukiwi (South Island snipe), we need to look to a different approach – gene technology. Despite all that we can now do with gene technology, this is still a difficult prospect.

The first thing we need to do is recover the DNA of the extinct species we want to bring back. If we are looking at a very recently extinct species, there might be material which has been stored with that precise aim. In such cases, recovering the entire set of genes, known as the genome, would be straightforward.

For most species, though, we will only be able to recover fragments of DNA. This can be done either from museum specimens or inadvertently preserved material, such as material from certain types of fossil. Piecing the fragments together is not like doing a jigsaw, because although we might have a reasonable idea of what the animal looked like, this doesn’t tell us much about its genome. The main approach to reconstructing a whole genome is to start with the genome of a related species and use that as a guide to where the genes should go. This has worked to some extent with species such as woolly mammoths, which shared a common ancestor with elephants only 3-5 million years ago. However, in attempting to recover the genome of an extinct rat species which had several living relatives, scientists found that they still had significant gaps, more than 4% of the genome. The rat species they were studying had shared a common ancestor 2.3 million year ago. Reconstructing the genome would be a great deal harder with any moa species, since they diverged from their closest living relatives, the tinamous of Central and South America, around 60 million years ago.

Assuming we can get something resembling the genome of an extinct animal, it’s still a long way from having a living animal. The easiest way, and one which bypasses the difficulty of getting the reconstructed chromosome into a living cell, is to genetically modify a related species so it resembles the extinct species. The problem here is that there’s a large gap between the number of genetic modifications we can practically make and the number of differences between, for example, an elephant and a woolly mammoth. It doesn’t sound like much when I say that the two species have more than 99% of their DNA in common. However, that still works out to around 1.4 million individual differences in the chemical code. I haven’t been able to figure out exactly how many changes we can now make at once, but in 2017 the most we had managed was 62.

To put things in perspective, the “dire wolf” which was hyped in the media earlier this year was created from a grey wolf genome with around 20 genetic changes. The scientists who created it modified traits which they considered important – mainly focused on appearance. The genome, though, is still a long way from being that of a dire wolf. And the genetic modification process still involves cloning, with all the difficulties that represents. So they won’t be resurrecting the moa any time soon, no matter what the hype says.

Soon, we may achieve the de-extinction of a very recently extinct species, one where we managed to save some whole cells and store them correctly. But if we don’t have cells and are working from DNA fragments, then it’s a different story. We can create genetically modified animals which resemble extinct animals in various ways. In future, I’m sure that we will be able to recover DNA better from museum specimens or other material, and make larger numbers of modifications, so that the genetically modified animals will be even closer to extinct species. How close? That isn’t clear, but I think it’s debatable whether animals created in this way can really be considered the same as the extinct species.

Process for “de-extinction”, which is really just modifying related species to have a few extinct species genes (image credit: Melanie Newfield)

Even if we could, that doesn’t answer the more important question – whether we should. The idea certainly has appeal. I’d love to see huia scampering up and down the branches of our forest trees, to hear the doleful shriek of the whēkau and to know that somewhere in the distant hills there were moa. I’d love to admire the blooms of Adams’s mistletoe, or some of Hawai’i’s lost hibiscus and lobelia species. I’d love to know that the Australian thylacine and the quagga of South Africa and the tortoises of Mauritius and Rodrigues still existed, even if I never saw them.

But this doesn’t mean that it’s a good idea. As much as I want all these extinct species to exist, I’m not convinced that what is possible within the foreseeable future would really be bringing them back. Nor am I convinced it is a good use of resources. The efforts I’ve written about are hugely expensive, and we are struggling to protect the species we have. We have brought species such as the tīeke back from the brink simply by providing it with forests free from introduced mammals. But others, such as the kākāpō, kakī (black stilt), karure (black robin) and tuturuatu remain critically endangered despite our efforts. If we can’t stop species becoming extinct – and at the moment it certainly seems as if we can’t – then is there any point in bringing them back only for them to become extinct again?

One reason that species such as karure are still critically endangered is inbreeding. All of the karure in existence are descended from a single female bird, known as Old Blue. The birds are extremely inbred, which results in poor survival of young birds and vulnerability to disease. For de-extinction to really help conservation efforts, we will need to restore genetic diversity rather than bring back a pair of animals. What is currently proposed seems more like a high-tech version of an old-fashioned zoo – the kind which displayed animals for our entertainment rather than being part of genuine conservation efforts.

There’s also an argument that if we can bring back extinct species, that will become an argument to put less effort into conservation – a moral hazard argument. I’m don’t think I agree with this one. To me, that’s like saying we shouldn’t develop treatments for preventable diseases, because people then won’t get vaccinated or practise safe sex. Perhaps that is partially true, but I still think we should have treatments for preventable diseases.

There are valid arguments that some extinctions have endangered other species, as is the case with the extinction of tortoises and the dodo in Mauritius. In these cases, it could be argued that de-extinction may have a wider conservation benefit. However, the tortoises from Aldabra seem to be achieving the same aim, at a fraction of the cost. Would it really be worth the expense of creating a version of the Aldabra tortoise which has been genetically modified to be more like Mauritian tortoises? In the majority of cases, I suspect that the answer will be no. There are still issues with using these so-called analogue species, but they are surely less than using genetically modified and cloned animals which have some resemblance to the extinct species.

I do think that it’s worth considering the idea of preserving material which could be used to clone our most endangered species. Even if these species don’t become extinct, this may help us preserve more genetic diversity. But gene technology and cloning are a long way from bringing back species which are already extinct, and it’s not clear that this will ever be possible. Despite the hype, extinction is still forever.

1. There are extinct plants, as well, of course. However, most discussions are about reviving extinct animals. The process for plants is also likely to be quite different because they reproduce very differently.