Scientists Study How We Evolved To Stand On Our Own Two Fins

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By Scott Neuman

Scientists examining an unusual African fish that can walk and breathe air think they’ve learned a thing or two about how our distant ancestors made the leap from the oceans to terra firma some 400 million years ago.

The modern fish they studied is called Polypterus senegalus, which has both gills and lungs, as well as a remarkable ability to use its pectoral fins for locomotion. The lobe-like fins are positioned so the fish can walk, albeit awkwardly. Polypterus “looks very similar to the ancient fish that eventually evolved into tetrapods. That’s why scientists examined this species in order to learn a bit more about its unusual characteristics,” Science World Reportsays.

The Toronto Star writes that the results of the study, carried out by researchers from McGill University in Montreal and published in Nature, “suggest much about the evolution of complex pieces of anatomy such as arms and legs.”

“What we wanted to pin down was: If you change the environment of this fish, does it change its behavior or does its anatomy change?” said Emily Standen, now at the University of Ottawa.

22 COMMENTS

  1. I have come up with an argument that really smokes the believers and leaves them speechless . . . . it follows . . .

    “Can anyone imagine the logistical nightmare of trying to crowd 7,770,000 species inside a small ship of only 2,033,500 cubic feet? Even ignoring the fact that they would not fit, can you image one family organizing this, preparing the ship, all the provisions . . . today?

    Keeping them from eating each other, feeding them every day for about a year . . . . hauling out all the dung . . . . on a ship at sea?

    24 hours x 60 minutes =1440 minutes a day
    1440 minutes a day x 60 seconds = 34,560 seconds per day
    7,770,000 species / 34,560 = time allotted to feed each species, and clean out their dung . . . . in seconds per day = .0044479 seconds

    Well, I guess that blows that theory out of the water, and that is not even considering that species come in pairs, that those who feed the animals must feed themselves, defecate, and sleep . . . . ”

    Feel free to or use it, revise it, or edit it!

  2. Anatomically, their pectoral skeleton changed to become more elongate with stronger attachments across their chest, possibly to increase support during walking, and a reduced contact with the skull to potentially allow greater head/neck motion.

    As I frequently say, this is not my field, but is this seems to be coming close to Lamarckism, without actually saying so. I suppose the answer is that those finny ancestors who were better at turning their heads, or walking along dressage style, were the best breeders – but still, it raises the question about how the first generation acquired these characteristics, how they were able to develop them and pass them to the next generation, and how subsequent developments occurred in their descendents.

    Don’t worry lads, I don’t think it was Himself.

    • eejit Aug 30, 2014 at 12:31 pm

      Anatomically, their pectoral skeleton changed to become more elongate with stronger attachments across their chest, possibly to increase support during walking, and a reduced contact with the skull to potentially allow greater head/neck motion.

      As I frequently say, this is not my field, but is this seems to be coming close to Lamarckism, without actually saying so. I suppose the answer is that those finny ancestors who were better at turning their heads, or walking along dressage style, were the best breeders – but still, it raises the question about how the first generation acquired these characteristics, how they were able to develop them and pass them to the next generation, and how subsequent developments occurred in their descendents.

      That is an easy question for any marine biologist.
      A whole host of marine animals including vertebrates, walk along the sea floor on fins or appendages.

      Only a few (when deprived of the buoyancy water for support) walk up beaches, or have adapted to low-oxygen conditions requiring other breathing mechanisms to supplement their gills.

      The origin of tetrapods – http://evolution.berkeley.edu/evolibrary/article/evograms_04

      Mudskipper: The Walking Fish – http://www.youtube.com/watch?v=mJhUKzEq47U

      However, on any tidal shoreline, there will be organisms which can tolerate varying amounts of exposure to sunlight, wind, and rain, according to how far up or down the beach they are situated.

  3. Doesn’t this answer the frequent question from Creationists, “how come we never see anything evolving today?” This fish is a perfect example of something evolving from one form to another, isn’t it? I mean, it has gills and lungs, right? It’s a fish that is walking on land! What more could you possibly ask for?

    • Strange how creationists require proof of others but ignore that requirement in their own thinking. Invoke the 2 infinite variables god and satan and all answers are not merely possible but easy to acquire and it removes the necessity to think any further.

    • I’m not sure that it is evolution. There is no evidence of genetic difference having developed between the control group and the experimental group. The differences seem to be due to the action of the environment on the pre existing organisms. Where did this specific adaptive ability come from, and how would the animals in nature have maintained it, if they did not use it?

      • No, it isn’t evolution. It’s plastic development. Development: changes in an organisms over time; Evolution: changes in a population over time.

        In some ways it plays into a creationist fantasy that adaptive change is not a result of Darwinian processes but of pre-designed “front-loaded” plasticity that allows individuals to adapt in response to environmental change, and possibly pass those changes on to their offspring in a Lamarckian manner. That’s why creationists and IDists are so keen on epigenetics.

        But it does have implications for Darwinian evolution of tetrapods, by means of the Baldwin effect, by which plastic changes that enable individuals to exploit a new niche alters the adaptive landscape such that that niche becomes “elevated” – there will be positive selection of traits that best enable an individual to exploit that niche better than its fellows.

      • Sorry, I didn’t mean that the study was evidence of evolution in action. I meant the fish itself is evidence, since it clearly seems to be in a transitional state between a sea-dwelling creature and a land-dwelling feature. “You expect me to believe that millions of years ago a fish just decided to walk out of the water and start walking on land?” Sure, in fact, here’s a fish doing it right now…

        All life is a product of evolution, no?

        Well, yes. Obviously. But Creationists don’t see things that way. They want “proof” of evolution, which usually means either a transitional fossil (showing some characteristics of one species and some characteristics of a completely different species) or evidence that some species is clearly evolving into a completely different species right before our very eyes. Obviously, all life is currently in the process of slowly evolving from whatever species are distant ancestors were to whatever our distant descendants will someday become, but that’s not good enough for Creationists. No, they won’t believe it until they see a creature that is half crocodile and half duck.

        Of course, we all know that if a crocoduck ever did get waddle onto the scene, the Creationists would just claim that it proves nothing since God obviously made it that way…

        • godzillatemple Aug 31, 2014 at 3:31 pm

          Sorry, I didn’t mean that the study was evidence of evolution in action. I meant the fish itself is evidence, since it clearly seems to be in a transitional state between a sea-dwelling creature and a land-dwelling feature.

          I think this explanation, tracks the evolution.

          @OP – link http://www.polypterus.info/
          The Polypteridae are ancient, snake-like fish whose origins date back to the time of the dinosaurs! All of the present-day Polypterids come from the freshwater rivers and lakes of Africa. They are able to breathe air via a lung-like modification to their swim bladder,

          What we have here are fish which have adapted their breathing to the oxygen depleted waters of lakes, ponds, and swamps, by supplementing (or replacing) oxygen via their gills with the oxygen from a gradually modified evolving swim-bladder. (A similar adaptation to frogs absorbing oxygen through their skins). Oxygen depleted waters are often depleted because of rotting organic matter which also makes visibility poor, so many species in such environments crawl along the bottom, feeling their way.

          There are of course quite a few living species of fish which can come out of water and cross areas of land. – Such as eels or walking catfish!
          Walking Catfish in Florida – http://www.youtube.com/watch?v=mjaJdDPHZTQ

    • No, it doesn’t. A single fish growing up as a walking fish is not an example of evolution, it’s an example of development. Development: changes in an organism over time; Evolution: changes to a population over time.

      To some extent it plays into some creationist fantasies – that it’s not Darwinian processes that cause adaptation but pre-designed, “front-loaded” plasticity that enable organisms to respond plastically to a new environment.

      There’s a discussion on Talk Rational about it, with Per Ahlberg participating, here.

      One possible link with evolution (which Per is a bit dubious about, but it’s still potentially interesting) is the Baldwin effect, whereby plasticity allows an organism to occupy a new niche, thereby upping the competition between individuals whose genetics best allows them to thrive in that niche, and thus leading to a fitness landscape in which that niche is “elevated”.

        • Sure, the fish is the result of evolution. But the behavioural and morphological changes that the authors observed were due developmental plasticity in response to an environmental change, not evolutionary adaptation to the new environment.

          • Thanks for that Elizabeth, but I’m still left confused about how the observed developmental plasticity in the individual fish, relates to evolution. Do the head turning, dressage walking fish have to hang around until a suitable mutation occurs, when they can spread the gene amongst the gang, and move on to the next stage?

          • Well, it doesn’t necessarily.

            But it firstly indicates that modification of gene expression by the environment can result in a walking fish, suggesting that modification of actual regulatory genes could do the same.

            Secondly there is a mechanism called the Baldwin effect (check the wiki link I gave) by which plastic changes that help an organism exploit its environment essentially create competition between individuals to exploit those changes and thus result in selection of traits in which those features are genetically “hard wired” as it were.

            Check out Per Ahlberg’s comments though in that Talk Rational thread. He’s one of the world’s leading researchers on tetrapod evolution.

  4. I don’t think this is evoultion. But this fish can give us a lot of ideas how the ancient fish developed their fin when they colonized a new environment.
    Of course, this fish means nothing to creationists. , All they have to say is: “Well, see? It’s still a Polypterus senegalus, right? It’s still in the same baramins or kinds.”
    The real interesting part is when creationists ask for a “transitional form”, it usually means you need to give them a creature or a fossil that must match their own imagination or invented creature. Like the crocoduck (So , why don’t the creationists call the platypus an “duckotter”? Correct me if I’m wrong, but isn’t that a duble standard? ) So, they can almost deny any transitional fossil, and keep yapping their “baramins”. You can’t win these people.

  5. Yue Aug 31, 2014 at 10:45 pm

    Of course, this fish means nothing to creationists. , All they have to say is: “Well, see? It’s still a Polypterus senegalus, right? It’s still in the same baramins or kinds.”

    The terms “baramin” and “baraminology”, were invented so that ignorant kids could be told by YECs to look up the cretinist’s pathetic attempts to write a classification system (based on the KINDS of animals on Noah’s Ark) as a simplistic alternative, avoiding them seeing the evolution based INTERNATIONAL CODE OF ZOOLOGICAL NOMENCLATURE – http://iczn.org/iczn/index.jsp, which is used world-wide by REAL scientists to classify zoological species!

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