In the late 2000s there was a lot of talk about how the Tasmanian devil was going to go extinct because of devil facial tumor disease. I expressed the thought that we need to be really cautious thinking that disease could drive the devils to extinction. This was not based on detailed knowledge of the biology of the devils. It was based on the fact that complex organisms are often subject to disease, and populations do crash, but it is clear that even if census size gets rather small, unless a population is very small and restricted disease itself and alone probably won’t eliminate an organism because there will be an evolutionary response. That’s one of the main arguments for why complex organisms tend to be predominantly sexual lineages despite the process’ two-fold cost. From what I recall many of the researchers expressing alarmist sentiments were ecologists, who often do not have evolutionary responses foremost in their mind.
But, there are reasons to be worried. The devil went extinct on the mainland ~3,000 years ago. The reason was probably the same as with the Tasmanian tiger: competition with the introduced dingo dogs. Probably more dangerous to the long term viability of the devil is that it is now restricted to an island the size of the Republic of Ireland (and much of the habitat on Tasmania is not devil optimal), where it is subject to habitat loss, and competition with introduced species.
Mind you, I am somewhat worried about the possible loss of the devil. But I thought it was frankly somewhat sensationalistic to assume that the devil’s disease was sui generis, and we just happened to be living at the time when the whole species was going to go down after persisting in Tasmania for ten thousand years despite various ups and downs. Diseases come and go. What is sui generis is the terraforming inclinations of our own species. We are the necessary and often sufficient condition.
A new open access paper suggests I may have been on the right path, Rapid evolutionary response to a transmissible cancer in Tasmanian devils:
Although cancer rarely acts as an infectious disease, a recently emerged transmissible cancer in Tasmanian devils (Sarcophilus harrisii) is virtually 100% fatal. Devil facial tumour disease (DFTD) has swept across nearly the entire species’ range, resulting in localized declines exceeding 90% and an overall species decline of more than 80% in less than 20 years. Despite epidemiological models that predict extinction, populations in long-diseased sites persist. Here we report rare genomic evidence of a rapid, parallel evolutionary response to strong selection imposed by a wildlife disease. We identify two genomic regions that contain genes related to immune function or cancer risk in humans that exhibit concordant signatures of selection across three populations. DFTD spreads between hosts by suppressing and evading the immune system, and our results suggest that hosts are evolving immune-modulated resistance that could aid in species persistence in the face of this devastating disease.
Again, we need to be cautious about these results. They’re preliminary. Just as we needed to be cautious about the original extreme claims.