Duhhh. . . . Guardian touts a “new” finding that thylacines are more closely related to kangaroos than to dingos

December 11, 2017 • 1:15 pm

Below is the headline of a new science piece in the Guardian (click on screenshot to read it), reporting on a paper that was just published in Nature. I haven’t read that paper, so I won’t comment on it; rather, I’ll comment on the science writing, which in this case is abysmal. It’s sensationalistic, misleading, and, sadly, the scientists whose work is reported appear complicit in the sensationalism.

But what’s a thylacine? It’s a fascinating creature: a carnivorous Australian/Tasmanian marsupial (Thylacinus cynocephalus) that looked like a dog. It’s been called the “Tasmanian wolf” or, because it was striped on the back, the “Tasmanian tiger.” The species lived until recently, going extinct in Australia about 2000 years ago (sightings are reported in the 1830s, though), and on Tasmania until 1930, when the last known one was shot. (Sightings are still reported there, but none have been credible.) Here are two from a Washington, D.C. zoo in 1906:

Why did they go extinct? Certainly hunting was a major factor, but others that have been suggested are disease, habitat loss, and competition with dingos. Dingos are the descendants of wild canids introduced into Australia, and are, unlike thylacines, placental mammals. The physical resemblance between the thylacine and a canid is an independent evolution of form, or an evolutionary convergence. 

There are two results given the headline: “genetic weakness” of the thylacine and “the closer relationship of the thylacine to kangaroos than dingos”. We’ll take these in order.

First, the “weakness”, which I take to mean “lack of genetic variation”, which could make a species more susceptible to extinction because it can’t evolve in a way that would help it cope to new environments or conditions like disease. (Evolution requires genetic variation.) The paper reports a genomic sequencing of a preserved, 106-year old thylacine. Since I haven’t read the paper, the lack of variation in the species would have to have been deduced by finding that this individual was largely invariant in its genome: that both copies of every gene were more similar than in other species.  But earlier work in 2012, based on several thylacines, already told us that they were largely invariant in their mitochondrial DNA. So this conclusion isn’t new.

Did the thylacine go extinct because it was genetically depauperate, though? We have no idea, and the Guardian even suggests it didn’t:

“But what we found is that the population declined about 70,000 years ago, long before it was isolated meaning it probably had more to do with changes in the climate back then.”

While overhunting was “without doubt” responsible for the animal’s extinction in 1936, Pask said its genetic weakness would have made it more susceptible to disease had it survived.

Yes, and if my aunt had testes she’d be my uncle. What we have here is pure speculation. It does appear that thylacines were genetically depauperate, but whether that played a role in their extinction is unknown. After all, they were shot willy-nilly.

But the worst part is the second “conclusion”: the breathless report that thylacines are more closely related to kangaroos than to dingos, with a quote from associate professor Andrew Pask from the University of Melbourne (my emphasis):

The researchers also found that despite its similarities to the Australian dingo, the thylacine’s DNA actually has more in common with the kangaroo.

Scientists consider the thylacine and the dingo as one of the best examples of what’s known as “convergent evolution”, the process where organisms that are not closely related independently evolve to look the same as a result of having to adapt to similar environments or ecological niches.

Because of their hunting technique and diet of fresh meat, their skulls and body shape became similar despite the Tasmanian tiger’s DNA having more in common with a kangaroo.

Pask said the genome showed the Tasmanian tiger was an “unbelievable” example of convergent evolution, because it proved how distant the two species were.

“Their similarities are absolutely astounding because they haven’t shared a common ancestor since the Jurassic period, 160m years ago,” he said.

For crying out loud, WE ALREADY KNEW THIS! Thylacines are marsupials, like kangaroos, and dingos are placentals, like dogs and most other mammals we know. They belong to different infraclasses of mammals (the next level below the class Mammalia), and their ancestors separated about 159 million years ago. In contrast, the thylacine and kangaroo last shared a common ancestor about 62 million years ago. We’ve known that this is a case of convergent evolution for decades, and no biologist would be surprised at the subheadline above. They’d say, like Greg, Matthew, and I did, “Yeah, so?”

You can attribute that subheadline, perhaps, to a nonbiologist interested in writing clickbait, but it appears that Dr. Pask is guilty for fostering some of this hype, for he knows full well that the relatedness and time data have been around for years.

As Greg said when we were discussing this piece (it was sent by Matthew Cobb), “Any scientist who can pretend, in order to garner press attention, that it’s a novel discovery that Tasmanian tigers are indeed marsupials should be shunned as a publicity-seeking charlatan.”

Amen!

67 thoughts on “Duhhh. . . . Guardian touts a “new” finding that thylacines are more closely related to kangaroos than to dingos”

  1. … no biologist would be surprised at the subheadline above. They’d say, like Greg, Matthew, and I did, “Yeah, so?”

    Hmm, I’m going to stick up for The Guardian a little. Yes, biologists would have known it, and it’s not new, but many readers of the Guardian would not know it and might find the article interesting and educational. And, for the article to be accepted by the editor of a newspaper, there has to be some “novelty” angle about it, even if a manufactured one. There’s few enough straight-science reports in mainstream newspapers that I’d be lenient on them.

    1. Well, I’d say that their responsibility, then, was to SAY that this finding is well known (as is the genetic depauperateness, which is also not new). There’s also plenty of good new science out that hasn’t been done before.

      But again, I’m going on this report, and vetting the journalism, not the original paper, which I haven’t yet read.

      1. (I was just firing up my OpenAthens login to see what was in this week’s Nature. Will have a read, and snarf the PDF for interested readers.)

  2. Heck, you don’t need to be a professional biologist to recognize that bit of silliness. You just need to know the difference between marsupials and mammals!

    1. “You just need to know the difference between marsupials and mammals!”

      Or, perhaps, between marsupials and placentals, you eutheriocentric chauvinist?

      I spent several hours helping another journalist with that paper (who wanted to know about the morphological convergence issue —- quite a few overstatements in that paper) and never even got an acknowledgement of receipt of my contribution. I’m vowing off talking to the press ever again.

      2. I love “eutherocentric chauvinist”!

        Journalist are sometimes bloodsucking parasites. Every time I talk to one I ask for a link to whatever they publish. I get that link only about 30% of the time. Ingrates!

          1. A harsh and sweeping judgement surely? Like most professions journalism has its good and its bad practitioners but it is in itself an important and useful job that they do. How else are we supposed to know what is going on in the world? As well as those journalists who are just peddling tittle tattle there are plenty risking their lives to keep us informed about what is happening and why in conflict zones and other dangerous environments around the world and it is often (usually?) thanks to assiduous investigation by journalists that the misdeeds of governments, corporations and other bastions of the powerful are brought out into the light of day.
            Of course journalists have to publish their work somewhere and the outlets for their work bear a big part of the responsibility for the degree of sensationalism, partisanship, integrity, etc in what they publish. This in turn reflects the demands of the market – sadly the Daily Mail and Fox News have much greater market share than more rigorous and unbiased news outlets. To some extent therefore the onus is partly on us to vote with our wallets/viewing/browsing habits to encourage good journalism and shun the bad.
            So, in short, by all means continue to call out bad journalism wherever it occurs but let’s not damn all journalists for the sins of a few any more than we would accept the notion that all scientists must be cheats and frauds because of the actions of a Jan Hendrik Schon.

  4. “As Greg said when we were discussing this piece (it was sent by Matthew Cobb), “Any scientist who can pretend, in order to garner press attention, that it’s a novel discovery that Tasmanian tigers are indeed marsupials should be shunned as a publicity-seeking charlatan.””

    Having had my words “interpreted” by the press to mean things drastically different from what I had said, I recommend a little forbearance. It is altogether likely that the scientist was simply trying to explain the basic facts to the reporter who then thought to couch his explanation in the manner of a “discovery” to put a little “sizzle” in the article.

    Many media types not only know little, they are not interested in facts because they are judged by audience response.

    1. Carl Zimmer is interested in facts. Why is everybody excusing the laxness of journalists? We should be holding their feet to the fire to make sure that, at a minimum, the science is presented accurately.

      1. I’m not excusing it, I just have no hope of changing it. The forbearance I suggested was for the scientist who may have been misrepresented.

        1. Further to the above, I have worked as a credited technical advisor on a TV series and as a technician on two Hollywood movies.

          The fact that I have no hope of changing it is based on experience.

          1. Agree completely. Once you go that route you have no real control. “Extinction events” in science stories are common. Quotes can be worse. In my own experience a journo will plant phrases and you end up being quoted saying something you’d never imagined, or completely out of context of a wider discussion. One option is try to do a live interview, at least then you have some direct control over what you are supposed to have said.

    2. That was unexpectedly hilarious.

      You know what else looks like a wolf? Any animal if photoshopped enough.

  6. If this DNA is comparatively recent – i.e. from a period not long before extinction – could the apparent lack of genetic diversity just be because the population towards the end was low and inbred, but tell us little about the genetic diversity when they were more common?

    In other words the low genetic diversity was because of impending extinction rather than the other way round?

    1. They only sequenced the one (as far as I can see from glancing at the paper, the sample was 108 years old.

      https://www.nature.com/articles/s41559-017-0417-y.epdf

      So it doesn’t tell you anything about diversity on its own. As they say themselves in the abstract they did this to “clarify the phylogenetic position of the thylacine within the carnivorous marsupials”

      3. The animals that were called marsupial cats are now better called quolls (Dasyurus sp.). In the same family than those “cats” (Dasyuridae), you will find marsupial “mice” and marsupial “rats”.

        In cas you didn’t know, there are elephant-shrews that are not shrews and far less elephants.

        And for the flying foxes… probably another big title in the Gardian: “Flying foxes are not foxes, true Englishmen should have known” 🙂

        1. Actually, elephant shrews (or “Sengis” as they’re often now called) are much more closely related to elephants than they are to shrews. They belong to a clade of mammalian orders identified by molecular genetics, and termed “Afrotheria”. As the name suggests, this group appears to have arisen in Africa, and includes elephants, sengis, hyraxes, sirenians, aardvarks, and the Madagascan tenrecs.

          1. You’re true, I should have said “far less shrews”. I know that they are more closely related to elephants than to shrews, but they are not representative of the “common” Proboscidae either.

    2. And that see urchins are not closely related to chestnuts. But food journalists suspected it already.

        1. You may hope, Fred, that we are not in the queue, but evolution suggests that we are.
          No species survives indefinitely.

          2. “No species survives indefinitely.”

            True, but they do not all end as dead ends like the dodo. Some leave some traces in a successor like the Neanderthals did.

          3. I do not think that Neanderthals have left any successor species (or maybe yes, if I think of some guys I know), Homo sapiens being either their cousin species (they coexisted during tens of thousands of yers) or maybe conspecific to Neanderthals. I think now they are rather considered to be different species but when I was studying biology 35 years ago, the anthropology professor at University of Zurich would call the Neanderthals Homo sapiens neandertalensis, i.e a subspecies of H. sapiens.

          4. The average human has about 2% of it’s DNA from Neanderthal ancestors, and similar amounts of Denisovan DNA. This finding was somewhat controversial when it came out (8 years ago? A bit longer?), but it’s quite well confirmed now and the variation between populations of humans is the subject of research.

          5. That average would be for Euro-Asians, no? As I understand it there is very little of that Neanderthal DNA that seeped back into Africa.

    2. This film shows that they would often place the whole of their hind feet on the ground, I mean including tarsus and metatarsus. Sort of switching between digitigrady and plantigrady, whereas canids are completely digitigrade.
      Does anybody know what kind of sound they produced?

      1. Yes and when they are in plantigrade mode they look a lot more like kangaroos than canids.

    3. True. Recently, I assembled images comparing marsupials and eutherians from public-domain photos. I selected ones that looked maximally similar. So I took a wolf photographed on snow, an almost monochrome image, to match the black-and-white thylacine photos, and thought how this poor species didn’t survive to color photography.
      I dream that one day they may reconstitute it, using sequenced genomes.

  13. From the conversation article it is clear the researchers were looking to see if the strong morphological convergence was mirrored with convergences in genetic sequences. They aren’t. That is interesting (though perhaps not unexpected). It was pure bad journalism that mangled their real findings into “thylacines closer to kangaroos: new discovery”.

  14. Hello everybody, please donate to my science project. I have a radical theory that needs DNA testing. It is my view that Dingos are actually more closely related to cows than they are to thylacines.

  15. they were largely invariant in their mitochondrial DNA.

    Question for Jerry or anyone else: couldn’t this be just a result of sampling bias? I.e. that we only have Tasmanian thylacine DNA to look at?

    After all, if the population that made it to the island was small to start with, then the Tasmanian thylacine varaince might not be representative of mainland thylacine genetic variation.

  16. I don’t know how it’s surprising to anyone in any way that a marsupial is more closely related to other marsupials than a placental mammal.

  17. Minor comment:
    The last known thylacine in the wild was shot in 1930; the last known living thylacine died 7 September 1936 in a zoo.

  18. Humans -and accompanying placental dogs turning into dingos- arrived in Australia at least 50 to 60.000 years ago (not far from the 70.000 years thhe Thylacine genome appears to have started to decline). The scenario where the Thylacine progressively went extinct and a small population survived in Tasmania -dingos never reached that island-, appears to be a reasonable explanation for the lack of genetic variation in the Tasmanian Thylacines. Same for TasmanianDevils (Jerry or other, please correct me if I’m wrong there, if that speculation is improbable).
    So, humans appear to be responsible, first the big works in continental Australia by causing the dingo, and later, very recently, finishing them off by bounty-hunting in Tasmania.
    I find that scenario, which is not new at all btw, quite plausible.

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