Mar 19 2013

We drive evolution

Cliff swallows’s wings got shorter to survive on road.





We see a sharp decline in bird mortality over the last 30 years. It is not even 100 years that birds getting killed in America. But birds have already evolved to have shorter wings. Can changes take place so quickly? I am amazed. But is it true?

Let’s see what scientists say.

Eighty million US birds are killed by traffic each year. Cliff swallows (Petrochelidon pyrrhonota) have taken to nesting on road bridges, so may be especially vulnerable.

Charles Brown of the University of Tulsa in Oklahoma has been picking up dead swallows for 30 years. Roadkill numbers have steadily declined since the 1980s, even as the number of roadside nests has risen. The killed birds have longer wings than birds caught in mist nets for research, and on average the caught birds’ wings have got shorter.

It makes sense: shorter wings are better for a quick vertical take-off, and improve manoeuvrability.

“Everything fits with the idea that it’s vehicular selection,” says Ronald Mumme of Allegheny College in Meadville, Pennsylvania.

So, evolutionary changes have been occurred not by ‘natural selection’ but by unnatural selection, artificial selection, practical selection or vehicular selection! Isn’t it amazing?
Birds get killed by feral cats too. But they have to survive. Birds with Shorter wings are better to escape quickly.

Cliff Swallows are the new victims of human influenced evolution! We have made fish grow quickly!
Roads, vehicles, humans’ commercial greed are perhaps part of nature. We should think twice before calling those selections unnatural selections.


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  1. 1

    Artificial selection, from the way I see things, involves humans making decisions about the traits they are looking for in a breed or species, such as dog breeding. In this case, the vehicles, while made by humans, have become part of the environment of the birds, and there is no intent on any human’s part to breed shorter wings. So while the cars may be artificial, this is still a case of natural selection IMHO.

    1. 1.1
      No One

      Human beings are part of nature. I find it amusing that we categorize things as natural or unnatural. It’s all part of the same universe.

      1. Kilian Hekhuis

        “Human beings are part of nature” – It wholly depends on what you define to be “nature”. In common understanding, “nature” refers to biology, not technology.

        1. No One

          In common understanding wind, waves, volcanoes, and gravity are part of nature. So are birds nests. Humans consider themselves and their artifacts as separate. But they are not. Common understanding is flawed.

    2. 1.2
      Kilian Hekhuis

      “this is still a case of natural selection IMHO” – IMHO, there’s very little IMHO about it. If the birds weren’t selected by humans, the selection is natural, just as the selection of the famous Peppered moth went from white to black to white again, even if it was triggered by humans (heavy pollution).

  2. 2
    Kilian Hekhuis

    Seconded. But wait… this is bound to be micro evolution, isn’t it?

  3. 3
    Kilian Hekhuis

    “Better able to eat the insects stuck on their wings.” – You misread the article Taslima. It says “birds with shorter wings were better able to capture the remaining insects still on the wing”, i.e. the insects still flying (as in: not dead).

    1. 3.1
      Taslima Nasreen

      I did not think insects were dead. Anyway, I deleted that part. I do not think it is a good cause for shorter wings.

      1. Kilian Hekhuis

        Well, according to the article, apart from the human-driven evolution, a major factor may be a recent starvation caused by lack of insects, which allowed short-winged specimens to catch the remaining insects. So it may not be only, or even predominantly, human-driven, but the result of a “lucky” event that was not human-driven, but allowed the remaining birds to more effectively dodge traffic.

        1. Taslima Nasreen

          Thanks for your advice. Now that part is restored. Anything else?

          1. Kilian Hekhuis

            No, I think that’s it :)

  4. 4

    RE: “Scientists what us to believe it [evolution].”
    It isn’t a belief when you have evidence. You don’t have to take it on faith, you just have to explain the data. And Mobius is correct; this is natural selection.

  5. 5
    Taslima Nasreen

    It is not about believing in evolution. It is about believing in certain studies. Some times some evidences that some scientists show, are not very convincing.

    1. 5.1
      Kilian Hekhuis

      While true, if they are genuine scientists, they don’t “want us to believe” anything, they want to present us with their conclusions (hypothesis) based on the evidence they have gathered. By saying “scientists want us to believe X”, you use framing language often used by creationists, environmental denialists and the like. This may be due to less-than-optimal command of the English language, so it is worth pointing out. Having read the article you linked to, it seems that at least their evidence gathering (measuring the wing sizes of road-killed birds) is ok, and given that they explicitly mention an alternative to their hypothesis (at least as a contributive factor) makes it seem legit. Since I haven’t read the study, it’s difficult to say whether they tested alternative hypotheses (e.g. driven purely by changes in prey, or sexual selection etc.).

      1. Taslima Nasreen

        I still have doubts. I think thirty years or so time is too short for birds to evolve to have shorter wings. I do not believe in every study scientists produce. Like I do not believe in bigfoot thing. Remember a team of DNA scientists published their study on Bigfoot DNA? http://www.huffingtonpost.com/2013/02/14/bigfoot-dna-results-final_n_2681135.html

        1. Kengi

          That Bigfoot “study” wasn’t actually published in an actual scientific journal. It wasn’t science, which is why you should doubt it.

          I’m not sure what you base your claim of 100 years being too short of a time for a species to evolve shorter wings it. Can you link to a valid study which demonstrates this claim?

          There are many evolutionary forcings which can produce rapid changes in species. One forcing you need to consider is the reproduction rate of the species. The more generations per time period, the less actual time it takes to reinforce changes in the species.

          Another major factor in rapid changes is the size of the population in question. The smaller the population, the more rapid changes can occur. See, for example, this well-cited peer-reviewed article from an actual science journal:


          You may then want to search Google Scholar for other studies which have researched the rate of evolutionary change and how they occur. DNA studies, for example, have demonstrated that changes in even an individual protein can have a major morphological impact when those genes are expressed. It doesn’t take too many generations for that change to establish itself if the correct forcings are in place, such as a rapid change in environment.

          Usually those rapid changes happen when a subset of a species migrates and establishes itself in a new environment, but that’s functionally equivalent to having the environment change rapidly around an existing species.

        2. No One


          Here is a Nat Geo article about the rapid evolution in lizard stomachs:


          The changes happened in 36 years.

          1. Taslima Nasreen

            Cool. Thanks.

        3. Kilian Hekhuis

          “I still have doubts. I think thirty years or so time is too short for birds to evolve to have shorter wings.” – It’s not the years that count, but the number of generations. Small song birds typically produce a new generation every year, so you’d have thirty generations. That’s quite a lot, and more than enough to have a variation in the size of a specific part of anatomy be restricted to a smaller ranger, if that range is more advantageous. If I understand correctly, the study concerned average wing length, and did not claim that the minimum wing length has changed.

  6. 6

    The article you pointed to failed to provide any sort of link to actual science, so it’s right to have doubts since journalists often fail to properly report on what the science or scientist actually said.

    A quick search in Google Scholar failed to produce any recent published studies on wing size in Cliff Swallows by either of the two people mentioned in the article, so it’s impossible to evaluate the science from just that reporter’s small amount of text. No part of the basic claim, however, disagrees with well established evolutionary science. In other words, while it’s an interesting observation, it’s not an extraordinary claim (like the Bigfoot nonsense was).

    If you mean to continue to present opinions on science, perhaps you should read up on how to read a scientific paper as a start, then always look for the paper a popular article is based upon. Before making a scientific claim yourself, check with some experts in the field to see if they agree or not and why.

    Definitely learn how to use Google Scholar as well as PubMed when looking into the state of research in any field. Pay attention to what journals papers are in, and try to get a feel about their reputation, if any. For new papers, check which other papers the authors have cited to support any assumptions they make. See if that supporting citation has been cited by others or not.

    Most of all, though, instead of making wild claims of your own in a subject you know nothing about, do some research into that field to learn something about the processes involved. Ask questions when you don’t understand how something works.

    As has already been stated, scientists never ask for belief. They present conclusions based upon experimental evidence as well as assumptions from well-supported previous research. They always present that evidence for others to evaluate, and any critiques should be based upon that evidence rather than personal unsupported beliefs of your own.

    1. 6.1

      Here’s a nice recent article on how different characteristics of species, with special attention paid to physiological properties, can change or not even over the short time period of anthropomorphic climate change. It includes references to other studies on bird populations.


    2. 6.2

      One final thought about this particular claim. It could very well be that the population of Cliff Swallows being discussed already had a range of wing sizes covering everything from the smaller size mentioned in the blurb to the larger size. The observation may simply be that the new forcing of the new environment has eliminated most of the population with longer wings, leaving only the shorter wing birds in the population. This would still be considered an evolutionary change in the species, without even requiring a physiological change in individual birds.

      When talking about evolution, we need to always remember that we are talking about populations and not individuals.

      Of course, without access to the study, all of this is pure speculation…

      1. Kilian Hekhuis

        I see you beat me to it (see comment above) :)

  7. 7
    Taslima Nasreen

    Kengi, you are very harsh. Thank you for your advice though. You will definitely find many people who read and analyze research papers accurately and make perfect comments. I did not write this blog for a serious discussion on science. I have expressed my opinion on evolution of birds that I think by natural selection while the scientists think by vehicular or unnatural selection. I may sound stupid to you and many other experts. But stupid people also have the right to express their opinions. And there are also people who like to say and hear things that are simple and understandable. I believe in freedom of expression. I hope you do too.

    1. 7.1

      Of course I believe in your right to express bad information about science, and I have the right to correct it on a blog of my own. I’m particularly pleased you have given me the chance to correct it on your blog, which you didn’t have to do.

      And yes, I’m harsh. I apologize.

      1. Taslima Nasreen

        I do not think I have given any bad information. Please give me your blog address, I would like to read your blogs about science.

        1. Kengi

          I don’t have a blog, which is why I appreciate you allowing me to comment on yours.

          1. Taslima Nasreen

            Do you want to be a guest blogger? Send me your write up. I would publish if it is very good.

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