Railing about rails again: No, Science, it’s NOT THE SAME SPECIES!

May 17, 2019 • 8:45 am

UPDATE: Science has now corrected its post by issuing the addendum below.  As you’ll see in the comments below, author Alex Fox credits this post for the correction, which is gentlemanly of him. Thanks to reader Barry for the spot.


It is a truth universally acknowledged that the two most prestigious science journals in the world are Science, published in the U.S., and Nature, published in England. One would think, then, that their science reporting would be more accurate than the slipshod stuff you see in the science pages of the major media (the NYT is an exception). But Science slipped up this time when reporting on the independent evolution of flightlessness on the island of Aldabra twice: in an ancient white-throated rail that colonized the island and went extinct when sea levels rose, and then in more modern times (i.e., several hundred thousand years ago) when birds from the same flying lineage colonized Aldabra again and once again evolved flightlessness. (Islands lack predators and so flying, which is metabolically expensive, can often be dispensed with to gain other advantages.)

A few days ago I wrote about how nearly all the major media—tabloids and respectable papers alike—mis-reported this finding, saying that the two flightless rails were really the same species, one that had been “resurrected” or “had come back from the dead.” In reality, the three white throated rails (Dryolimnas cuvieri) are designated as subspecies, so even that reporting is wrong. But that’s minor compared to the repeated claim (see my earlier post for screenshots of the distorted headlines) that the very same species had evolved twice.

This was a big boo-boo because calling the modern flightless rail and its extinct flightless analogue members of “the same species” depended only on the similarity of two bones: a wing bone and a leg bone. There was no other fossil evidence, of course, about what the extinct rail looked like, how it behaved, or anything about the rest of its skeleton, its habits, its DNA, or its physiology. It’s simply a misleading whopper to assert that the “same species” evolved twice.

Further, the species concept used by nearly all evolutionary biologists deems two individuals members of the same species if, where they meet in nature, they can mate and produce fertile offspring. It’s a concept based on reproductive compatibility and incompatibility. Doing such a test is not possible in this case because the extinct species never had a chance to cohabit with the modern species. Just as we can’t say whether modern Homo sapiens are members of the same biological species as Homo erectus (note that they’re even given different names, but that’s based on physical differences), so we can’t say whether the ancient and modern flightless rails are members of the same biological species—much less subspecies.

As someone who spent his whole career working on speciation, including species concepts, I was thus disheartened to see this news report in the journal Science:

Note that while the report does call this “iterative evolution” (“convergent evolution” would be clearer to evolutionists), and notes the independent evolution of flightlessness, it also passes on Gizmodo’s report that evolution had “resurrected the lost species.”

Nope, that’s not true. We know nothing about the genetics, morphology, behavior, and physiology of the extinct species compared to the new one. Science had no business talking about “resurrection”, but it did.

Of course only a petulant evolutionary biologist who works on speciation would single out this error. But it’s pretty bad when one of the world’s best science journals makes a totally unwarranted claim like this.

35 thoughts on “Railing about rails again: No, Science, it’s NOT THE SAME SPECIES!

  1. Catchy headline writing, snappy writing seems to have gotten through the cracks – perhaps a new rule : when in doubt, write predictably. No poetic stuff. And don’t use attention-catching words like “resurrected”… I mean who says that?! Resurrected. That doesn’t ever happen ever.

    Im glad PCC(E) notes this stuff because I learned a lot from the rails story.

  2. Just wondering but does the Science Journal rely on subscribers to exist? And possibly sharp, but wrong headlines help sell it. It would still be no justification but maybe this is a PR guy.

    1. You can buy an individual subscriptions, but I would expect that most of their money comes through university subscriptions. Most scientists and academics get papers through their university’s subscriptions.

  3. I saw the item this morning and I was surprised to see the secondary reference to Gizmodo. The site does some reasonably good summaries of science news, but I thought it odd (and a bit lazy) that Science would rehash the Gizmodo report. Science has a staff perfectly capable of going back to the primary research paper and discussing it accurately. Again, the real news here is convergence and how it helps to illustrate evolutionary processes.

  4. Thank you for the science post which are always more appreciated than the number of comments might suggest.

  5. I didn’t read (couldn’t access) the article, but how did they confirm that it was in fact the re-evolution of flightlessness, rather than, for example the re-introduction (or back introduction) of the same flightless species from Madagascar? (There are other islands that appear to be within about 50 miles of each other that could link to Madagascar. I mean, if lizards made it over there, it’s not impossible that a flightless bird could too.)

    Did they sequence the genome of the two extant species to see how deep in time their relationship is, and were they able to sequence the DNA in any of the fossil flightless bird bones?

    1. The Science blurb is the entire article. If you mean the original one, I can get it for you if yu want to read it.

      The flightless species on Madagascar isn’t really flightless, and at any rate couldn’t get there from Madagascar. Plus the one on Madagascar is different from the extant one AND the extinct one.

      No, there was no sequencing.

    2. Did they sequence the genome of the two extant species to see how deep in time their relationship is

      Tropical islands with a reasonably damp climate are not a good recipe for preservation of DNA. Neither the heat, nor the presence of environmental water is good for preservation.
      The oldest fully-sequenced genome is from a horse in Alaskan tundra from about 700,000 years ago. That’s in excess of 40 Kelvin lower temperature.
      You might strike lucky and be able to get coherent sequence for a protein – one involved in binding mineral grains into bone, for example, and from that being able to infer a corresponding part of the DNA sequence, which you could compare with a homologous sequence from the inferred ancestor sequence. But one protein would be in the order of 0.003% of the coding genome, and an awful lot of genetics happens in non-protein-coding DNA (promoter genes, inhibitor genes, etc).

  6. Apart from the clickbait headline, is it possible in principle to conclude that the antique rail and the modern one could have interbred given sufficient information? For instance, suppose a good DNA sample could be extracted from the antique flightless rail bones to compare to the modern one and suppose the DNA was very similar. Is it possible we could conclude that they could have interbred? Would this suffice to label them the same species? Just curious.

    1. It’s always dicey to use DNA similarity to judge species status. For instance, a change in as little as one gene affecting a species habitat preference, or two genes affecting mate preference, could cause speciation, but you would still see a gross similarity of DNA sequence. There will of course be differences in DNA sequence between any populations, but it’s dicey indeed to use those to make proxy judgments about reproductive compatibility.

    2. s it possible in principle to conclude that the antique rail and the modern one could have interbred given sufficient information? For instance, suppose a good DNA sample could be extracted from the antique flightless rail bones

      See my reply to “Divalent” at #5 above.
      The tropics are not friendly to DNA preservation.
      Moisture is not friendly to DNA preservation.

      Is it possible we could conclude that they could have interbred?

      In palaeontology, we don’t generally dream of getting a sequence, we have to go on a “morphological species” concept. From what I’ve seen, we wouldn’t have grounds to call them different species, but we know that the “morphological species” concept is very inadequate. There have been a couple of bruising controversies going on in the Cretaceous of America (there, because of high sampling density, and an abundance of palaeontologists) for the last few decades over whether several species of the ceratopsian dinosaur family (Triceratops et al) are actually sexually dimorphic, or just closely related. Tyrannosaurs, lather rinse and repeat. Basically, we know that we don’t know. And that is in an area with hundreds of thousands of specimens of hundreds of species.

  7. No, it is not just an evolutionary biologist who would be upset. I am a geologist, and I’m upset.

    The idea of natural selection beginning back an extinct species is so impossibly improbable I’d think such an event would suggest that evolutionary theory is ripe for a major revision. It would be a MAJOR scientific observation.

    Instead, what actually occurred is cool and interesting, but within the bounds of what natural selection is expected to be able to do.

    Science Magazine should NOT be implying that an entire field is ripe for revolution!

      1. Well, I’m a one-time chemist (I took off my last lab-coat 44 years ago), and even *I’m* upset!

  8. The point here is that with successive convergent evolution, mutations that gave rise to similar external traits, such as the sizes of bones and flight ability, are almost certainly different. For example, there are numerous metabolic pathways (and mutations) that produce melanism in animals, and just because different species of melanic moths share the same wing pigment provides no evidence for homologous mutations.* In the case of Dryolimnas, as time goes on, and 100,000 years isn’t very long in evolutionary terms, the rail lineages would continually diverge on the biochemical level and inevitably (strong word?) undergo biological differentiation. Anolis lizards have done this on Caribbean islands.

    What I take home from the study is the speed at which wing reduction and ecological replacement (can the technical term “homology” be used here; the two birds appear to have homologous ecologies?) has happened. In this case adaptive evolution would indeed have resurrected, from a sister species, not the same species, but an identical or near-identical ecological role or “station in the economy of nature”, as Darwin might have put it.

    My skeptical side tells me not to discard the possibility that the extant flightless rail is a lineal descendant of birds that, against all odds, survived the catastrophic food. I await DNA evidence or 120,000-year-old fossils to resolve this question.

    *A figure in the following link shows how several different mutations in one receptor can give rise to melanism in mammals.

    1. What I take home from the study is the speed at which wing reduction and ecological replacement (…) has happened.

      Flight is expensive. Said the kiwi, the emu, the rhea, the dodo …

      I await DNA evidence or 120,000-year-old fossils to resolve this question.

      Put it at somewhere more likely than the lottery card coming up, but less likely than that ‘flu shot paying off. Certainly, don’t’ hold your breath waiting.

      survived the catastrophic food

      You didn’t let a Texan near the chilli bowel did you?

      1. Aldabra Atoll is said to be the home of hundreds of endemic species and subspecies of birds, lizards, insects and plants. A good but perhaps not impossible job of recovery, I’d say, for a place that was completely underwater 125,000 years ago (See Wikipedia and http://whc.unesco.org/en/list/185 )

        I have no quarrel with the assertion that wings are expensive and should tend to become lost where they become a drag. My view is that 100,000 years seems a short interval to obtain extreme wing reduction. The kiwi, dodo, and flightless Hawaiian goose were likely isolated on their island homes for millions of years to get where they did in historical times. That is why I suggested that great similarity of the extant species with the ‘extinct’ form may be due to ancestry and not eco-evolutionary convergence by a recent island invader.

        The fact that, despite feral cats, the island is rich in endemics, including a couple of land-birds, lizards, and a giant tortoise, suggests that during high sea-levels (the island has an elevation of abt. 8 m today), dunes now lost may have built up and allowed part of the old biota to survive.

        Another way to test whether Aldabra’s flightless Dryolimnas is derived from old stock vs. quickly evolved from a recent invader is by obtaining a molecular clock estimate of its time of isolation from its supposed sister taxon.

        I have not been able to download the pdf of the original paper and cannot comment on their evidence that the island had been swept clean.

        1. There’s something just a bit complicated about the assertions of the atoll being submerged in the vicinity of 125 kyr ago (136k, 100k, various numbers). At about that time, the global sea level was around 100m below the present. So, between ground movement and the loss / gain of height in the shell debris dunes, to have been submerged in that time range the atoll itself would need to have dropped in elevation by approximately 100m.
          Now, that’s perfectly reasonable. There’s a complex tectonic situation in that corner of the Indian Ocean (oh, 4 hours of papers in one morning on different contradictory plate motion reconstructions for the opening of the Indian- African- Malagasy-Comoros- South African- Antarctic multi-way junction ; the conference papers volume should be out soon. Hopefully I get some paying work out of it, eventually. ) and postulating a bit more of the old “land going up and down like organ stops” isn’t going to shock anyone. Well, no geologist, anyway.

          by obtaining a molecular clock estimate of its time of isolation

          Molecular clocks have a poor reputation for both sensitivity and accuracy, and for good reasons. Trust them with … caution.
          Feral cats typically follow people in their habitations, and the whole of that region is groaning with people needing land. While that persists, and I see no prospect of it ending, then the prognosis for the endemic species is not good.

  9. Thanks for writing this and for holding Science and myself accountable.

    Our story has been corrected.

      1. Although I appreciate your willingness to correct your mistakes, Alex, changing the title doesn’t go nearly far enough. The URL for your article (www.sciencemag.org/news/2019/05/evolution-brings-extinct-island-bird-back-existence) still asserts the magical re-evolution of an extinct bird, which Hume and Martill (2019) never claimed. In addition, I question a number of your other uncorrected assertions:

        1) What peer-reviewed reference led you to claim “iterative evolution” is a rare phenomenon?
        2) What source defines “iterative evolution” as you have?
        3) Why do you still argue that “nearly identical species [have evolved] from the same ancestor at different times” when you know Hume and Martill (2019) don’t make this claim?
        4) Finally, how does an ecosystem “cause” the evolution of flightlessness?

        Your summary is not drawn from Hume and Martill’s (2019) research; it is obviously drawn from someone else’s faulty summary of their findings. Your conclusions in the “corrected story” are the same misrepresentations of biological evolution that mislead the public in your original.

      1. Except you can willfully misread it, if you take it to be about how many times a bird can fly on the same island, and at what interval of time:

        “This bird lost the ability to fly twice on the same island, thousands of years apart.”

        It’s a wonder it had that ability in the first place!

        We often say a species evolved a particular trait, but we don’t seem to have a good way to say a species un-evolved a trait.

        Maybe “This bird twice lost the ability to fly on the same island, thousands of years apart” would be clearer?

  10. David Steadman’s 1995 paper (in Science)summarises fossil evidence suggesting that flightless rails – totalling many hundreds or perhaps more than 1000 species in all – formerly lived on almost every habitable island in the tropical Pacific until the first Polynesian colonists ate them into extinction.


    It seems that rails are very good at reaching remote oceanic islands, and almost invariably become flightless after doing so. Given those tendencies, it isn’t at all surprising that two separate, successive flightless lineages could have evolved on Aldabra. That’s a far more interesting evolutionary story than the “bird species evolved twice” idea being pushed by the media, and it’s all the more depressing to see Science repeating the same fake news.

    1. I agree, Dave – nearly all the science-news outlets missed the value of this research because the implanted raised-from-the-dead fantasy turned off their brains.
      I appreciate how challenging it must be for science-news journalists to read and digest the avalanche of published research, and then produce effective summaries. But this is a case of many such sites following the leader (BuzzFeed?) and repeating the same mistakes (e.g. The Smithsonian, LiveScience, ScienceDaily, ScienceAlert, IFLScience, and Science). Mistakes include:

      1) that a species re-evolved by natural selection,
      2) that “iterative evolution” is “extremely rare,”
      3) that “iterative evolution” is defined as “nearly identical species evolving from the same ancestor at different times,”
      4) and that the predator-free atoll ecosystem CAUSED the Aldabra rails to become flightless.

      I expect science gaffs like these from major media organizations like CNN, but not from good science-news outlets. Although I appreciated Mr. Fox’s improved title, much of the faulty content remains (including all four mistakes listed above). ANY qualified editor – hell, any qualified biologist – should have blanched at the claim of a species re-evolving (not just “a petulant evolutionary biologist who works on speciation”).
      I’ve found only one independently and competently written summary of Hume and Martill’s 2019 study – from the Natural History Museum of London (https://tinyurl.com/yymjlz7h).

  11. A small detail: “and then in more modern times (i.e., several hundred thousand years ago)”
    I was under the impression the last extinction of the flightless rails on Aldabra atoll was during the Eemian, only about 120.000 years ago.
    Or am I mistaken?

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