I spent Saturday down in Hawkes Bay, running at Scholarship Biology preparation day at Lindsfarne College. (I would have spent Sunday happily idling through the lovely Art Deco parts of Napier, & visiting a few vinyards, but the weather forecast made me reconsider this option & I ended up driving back to Hamilton once the teaching was done. But I still managed a most excellent very late lunch at Crab Farm Winery, nomnomnom. The wines are also excellent.)
Anyway, we finished the session by working through one of the questions in last year's Schol Bio paper, on whether mammoths (Mammuthus primigenius) could, & should, be brought back from the dead (as it were). As for the other two questions, candidates were provided with a lot of resource material about the biology, ecology and phylogenetic relationships of mammoths, and were asked to
Discuss how a modern biological technique could be used to bring mammoths back to life, and the implications of having mammoths living again. In your answer:
explain biological techniques that could be used to bring back the mammoth and produce a self-sustaining wild population. Evaluate the likely success of this process.
Analyse the evolutionary and ecological implications of having a population of mammoths living on earth again and justify whether or not we should bring back the mammoth.
(This is a question that I really wish I'd thought of - I'm seriously considering adapting it for an essay topic for my own students next year!)
This generated a lot of discussion, some of it very wide-ranging, & a couple of times I needed to remind everybody to focus on the question. The examiner wasn't asking for a consideration of the ethics around this concept, or for statements abotu the likely cost. Remember - it's really important to apply critical thinking skills to both the question itself, and to all the information you could potentially use to answer it. What info is directly relevant, and what's interesting, but not really applicable to the issue at hand?
The biological technique is fairly straightforward - scientists have been able to extract nuclear DNA from the tissues of frozen mammoths, so the most likely option is cloning. That is, placing this mammoth DNA in the fertilised, enucleated egg of an elephant and implanting that into a surrogate mother. Mammoths were roughly the same height as Asian elephants, but heavier & stockier, so African elephants would be the best choice as surrogates. Also, mammoths & African elephants apparently had 98% of their nuclear DNA in common, so their physiology should be similar, which might maximise the success of any resulting pregnancies. (Don't go into extra detail of how to do the cloning - the question is clearly about the use of this technique rather than how to carry it out.)
Now, the 'self-sustaining, wild population' part. If it's to be self-sustaining, then your mammoths will need to be breeding, so both males and females would need to be cloned. You'd also need to minimise the effects of inbreeding (as far as possible), so your clones would need to be from as many different individuals as possible. The more genetic variation in your population, the better. We talked quite a bit about the minimum population size to aim for, & the need to minimise the effects of inbreeding depression.
What are the odds of success? Very low. As things stand at the moment, the success rate for cloning is not high - between 0.1 & 3%. Researchers have to produce a lot of cloned embryos in order to produce just a few viable individuals, and for the mammoth resurrection to work you'd need many, & of both sexes. It's possible that cloned individuals may have shorter lifespans, if the telomeres from those cloned cells can't be re-set, and this would have implications for that self-sustaining population as some individuals might not reach reproductive age. And of course, with the surrogate mother coming from a different species, the odds are probably lower as well, nothwithstanding the similarity in nuclear genomes. (Differences in mitochondrial DNA could have an effect here.)
In evolutionary terms, even if we were successful in getting a population going, it probably wouldn't have much of a long-term future. A combination of the founder effect and inbreeding would see some alleles lost from the gene pool and others fixed, thus increasing homozygosity and reducing genetic variation. A likely outcome of this is inbreeding depression, where there's a drop in both reproductive success and overall survival.
As for the ecological outcomes - well, the most obvious question is, where would we put this population of mammoths? This particular pachyderm was very well-adapted to a climate colder than anything available now, so conditions today would be rather unsuitable for them. The only possible habitat would be above the Arctic circle, on the tundra of North America & Eurasia (it might well be cold enough in Antarctica but they'd definitely be short of things to eat!)
However, they would eat A LOT of food - at least as much as modern African elephants, & they chomp through 170-225kg of food each day. This would mean that existing consumers would be missing out, so their numbers would drop, & that would have a flow-on effect through the food chain. On the other hand, while polar bears & wolves probably wouldn't take on a full-grown mammoth, they could take down a calf. So a mammoth population could perhaps increase survivorship rates for those top predators. For a while - because as the herbivore populations decline this will affect the predators as well: big, K-selected mammals have a slow reproductive rate and there won't be very many baby mammoth to go round. The other thing is that elephants can be quite destructive, uprooting saplings & pushing over small trees. That, combined with their voracious appetites, would mean that the tundra ecosystem sustain considerable damage.
Which leads on to that last question - should we/shouldn't we resurrect the mammoths? The group was really doubtful about this. They tentatively suggested putting the animals in some sort of controlled environment, to minimise the risks of disease, and carrying out a selective breeding program to increase genetic diversity as much as possible. But, they said, why would you? The likelihood of a second extinction is high, so it would be a waste of resources that could be better put towards conserving existing species and their ecosystems. Plus someone pointed out that the African elephant is itself a conservation priority, so it seemed odd to be using one such species in a dubious attempt to bring back another. The lack of a suitable environment, the risks to existing species, and the impacts of low genetic diversity were also reasons why the students felt that we should not be putting mammoths back on the planet. There is more to taking a particular action, we agreed, than to do it just because we have the technology.