Breeding pre-history
Reintroducing extinct species is doable (if you’re not aiming for Jurassic Park), but which ones and how similar to the original?
The big thing in cutting-edge conservation is re-wilding – returning animals hunted to extinction to those environments they were once part of. Beavers have been returned to Scotland and Devon, wild boar to Sussex and wolves to Yellowstone Park, with more re-wildings planned. The next big thing, however, may be de-extinction – returning extinct creatures to life if not, perhaps, nature. All very Jurassic Park, but less ambitious: scientists are aiming for thylacines, mammoths and great auks rather than dinosaurs. Dinosaur blood from insects in amber (as in Jurassic Park) is too old to retrieve, and amber destroys DNA captured within it. However, museums have preserved specimens of more recent creatures from which reasonably intact DNA could be extracted to reconstruct their genome. This could then be inserted into the egg cells of closely-related species and brought to term in a surrogate mother.
The science for most of this is proven: it’s essentially work pioneered in stem cell research and cloning, so technically there is no obstacle to raising this kind of dead. However, there is a gap between it being technically and practically possible, and it is this gap that Beth Shapiro explores in How to Clone a Mammoth.
The complexity of de-extinction goes back to the selection of the species to bring back: carnivore or herbivore? Big or small? Naturally extinct or killed by humans? One that has an ecosystem to which it can be returned or one that needs it to be re-created? Then there’s the question of whether the genome can be extracted intact from preserved specimens or enough bits found for one to be stitched together – and if so, is this close enough to the original? Mammoths look like good candidates; there is a decent chance of getting good DNA from intact specimens preserved in the permafrost of Siberia. Thylacines – assuming they are extinct – are less promising: their remains are mainly preserved in alcohol or as chemically treated taxidermy specimens, and neither method is great for DNA.
DNA needs to be kept free of contamination, which is not as easy as it sounds. You need to get your DNA into the egg cell of a related species, and get that cell dividing as if it were an egg. This is how we got Dolly the sheep, so we know it works – for sheep. Every species is different: this process works for some but not for others. Dolly was the only one of 277 embryos that made it through to birth and she died prematurely because of problems originating in the cloning. For the one deextinction of an extinct animal to have produced a live result (that of the Burcado or Spanish Ibex), good-quality cells from a recently deceased donor were used – an individual’s cells had been banked when it was known that the organism was down to its last few specimens. The resulting creature lived less than 10 minutes because of problems similar to those that shortened Dolly’s life.
Shapiro makes it clear that whatever science we are capable of, de-extinction by cloning faces some major obstacles. She explores other paths, though. Could we breed our way back? By selectively breeding close relatives for features that make offspring most like the lost creature, could we come up with something almost identical? It takes time, but is possible; the Nazis did this to recreate Aurochs, the primæval cattle of the German Wald, resulting in a large, mean and unmanageable cow that closely resembles Aurochs. There’s been some success in returning ancient chicken breeds this way, but they are merely lookalikes.
Shapiro asks how authentic do de-extinct creatures need to be: would a hairy elephant satisfy those who want to return Mammoths or would it really need that similarity right down to the genetic level?
None of these questions is simple to answer, but Shapiro has done an excellent job in asking them.