Extinction, death and dinosaurs

The loss of a species was once thought to be as final as the demise of its last survivor but now, thanks to advances in biotechnology, reviving an extinct species is no longer pure fiction. But instead of asking “can it be done?” the conversation is changing to “should it be done?” The possibility of bringing species back from the grave – a process known as de-extinction – was widely popularised by Michael Crichton’s 1990 book, and Spielberg’s 1993 film, Jurassic Park. Inspired by the advent of genetic engineering, Crichton’s tale gained cult-status, but just as Aldous Huxley’s vision of artificial reproduction was brought closer with the advance of IVF technology, so the process of de-extinction has moved from sci-fi concept to real life science. In 2003, a team of French and Spanish scientists achieved the impossible task of bringing a species back from the dead, although only temporarily.

The Pyrenean Ibex was a large, mountain-dwelling member of the goat genus Capra that went extinct due to grazing pressure from domestic and wild ungulates in 2000. When the last Pyrenean Ibex died, its cells were preserved and, later, a nucleus from these cells was injected into a denucleated domestic goat egg, which was then implanted into a surrogate mother. In 2003, a clone was born. For the first time ever an animal had been brought back from extinction. Sadly, the baby ibex died shortly after birth due to lung defects. Rather than rejuvenating the Pyrenean Ibex, it served only to provide an unfortunate demonstration of the obstacles that remain in reproductive cloning technology.

Not only that, but of the 439 eggs used, only 57 developed into embryos, only four made it to full term, and only one survived to birth – a pretty poor survival percentage. Despite these problems, this breakthrough gave hope to the emerging de-extinction movement and, propelled by a combination of curiosity and conservation, many more de-extinction attempts are on the horizon.

The Tasmanian tiger and the passenger pigeon are just two of the candidates being vetted for resurrection. Furthermore, in March 2013, a team from the University of New South Wales announced that they were attempting to bring back the gastric brooding frog – a bizarre creature that used its stomach as a womb.

The birth of the ibex has also fuelled more ambitious and controversial ideas. For instance, could such technology be applied to ancient, long-dead species?

Unfortunately, it doesn’t seem like dinosaurs will be brought back any time soon as DNA decays with time, and cloning technologies require pristine DNA for success. Within hours of death, cells start the process of apoptosis, which releases enzymes that shatter DNA into an indecipherable mess. As it ages, DNA also undergoes chemical changes that alter the nucleotides – the base guanine changes into adenine, and cytosine changes to thymine.

So much time has passed that it’s inconceivable the full genome of dinosaurs such as Tyrannosaurus Rex, which died out around 65 million years ago, would have survived to the present day. Could a woolly mammoth be a more realistic goal? Disappearing between 6,000-10,000 years ago, well-preserved mammoths are routinely dug out of the Siberian tundra and scientists have been able to collect enough DNA fragments to piece the genome back together. Sadly, cloning requires much more than a reconstructed genome.

Artificially assembling DNA can be done easily with current technology, but free-floating DNA is of little use to a cell. The real challenge is packaging the DNA into chromosomes and inserting this into a nucleus. The shape of the DNA affects how it interacts with chemicals in the cell, and these interactions control gene expression, a factor every bit as important as the DNA itself. Finding a living mammoth cell would sidestep such difficulties, and a Japanese-Russian collaboration is currently leading the hunt for such a cell. The team plan to use a technique pioneered for cloning mammals from frozen tissue, which was successfully implemented on a mouse that had been frozen for 16 years.

The idea is for an elephant to then be used as an egg donor and surrogate to grow the properly packaged DNA. If a good soft-tissue sample is found, the researchers say a woolly mammoth could be born in a matter of years.

Even so, there is a great difference between bringing back an individual and bringing back a viable population. De-extinction would at best produce a handful of individuals that may or may not reproduce. And how can we engineer the mammoth’s social structure and behavioural adaptations? Despite these challenges, ambitious plans have already been made for a Pleistocene Park in North-Eastern Siberia.

In a similar spirit to the Jurassic Park of literary fiction, the dream is to restore the tundra to the mammoth steppe, a vast grassland habitat. Bison and reindeer have already been reintroduced, but the arrival of the mammoth may take a little longer.

Unsurprisingly, de-extinction is highly controversial. The implications of such initiatives are hard to predict, and there are questions regarding the well-being of the clones. Recent sequencing of Neanderthal DNA has made cloning the homo species theoretically possible, bringing us into unfamiliar ethical territory.

Even efforts to resurrect recently extinct animals are divisive. While advocates say that we have a moral responsibility to bring back the creatures we drove to extinction, critics argue that such strategies hinder efforts to save the habitats and species that remain.

Perhaps resources would be put to better use by boosting the populations of currently endangered species. In anticipation of this, San Diego Zoo has created the ‘Frozen Zoo’ project, a biobank storing tissue from over 1,000 extant species.

In a similar vein to the Millennium Seed Bank Project, it is hoped that the Frozen Zoo can help the survival of critically endangered species as well as providing a kind of insurance policy against extinction.

Like it or not, de-extinction technology does have a future. When science is this exciting we just can’t help being curious. After all, who wouldn’t jump at the chance to see a real life woolly mammoth? Whether or not it leads to the all-action sci-fi ending remains to be seen.

Find this article, alongside many more on the theme of life and death in I, Science this week!