That’s not how evolution works

Update: the BBC reports that North American bird species are getting smaller, likely in response to increased temperatures.

In a Mother Jones article, Julia Whitty says, “Birds are rapidly evolving different shapes to cope with clear-cut forests.” Now, she may be accurately quoting the source paper by André Desrochers, and she’s certainly not the only one to describe evolution this way, but that doesn’t make it any less misleading and stupid.

How Evolution Works (with only a trace of self-importance)

It’s not that hard to get it right. Evolution is the “…change in the genetic material of a population of organisms through successive generations.” [wikipedia] This happens because of two opposing processes:

  • Over time, the genetic diversity of a population tends to grow. Taking humans as an example, we have tens of thousands of genes. Each individual is a random mix of the genes of her parents, and is potentially a unique/novel combination. Each individual may also have mutations, making their collection of genes not only not a perfect selection of genes from her parents, but again potentially unique/novel. Finally gene transfer can also increase genetic diversity, although I don’t know of any proven instance of this happening in humans.
  • Opposing the increase in genetic diversity is natural selection. If a particular combination of genes is unsuccessful — if the person with those genes has bad eyesight and can’t hunt, or has a bad complexion and can’t get a mate — then those genes don’t get passed on, and assuming some other genes do, the species has evolved. (if other genes don’t get passed on either, the species goes extinct)

You can think of evolution as something like a bush in a topiary garden: left to its own devices it will simply grow larger — that’s genetic diversity at work; but if the gardener (in the form of natural selection) comes along and trims here and there, you end up with an elephant.

This is where the stupid comes in

If you have a four-foot-high bush, no amount of trimming is going to turn it into a ten-foot-tall image of an elephant. The article in Mother Jones starts with “A new study shows how North American birds have changed the shape of their wings in the past century as the landscapes around them have been fragmented by clear-cutting.” Bzzt, wrong. It’s not like at the annual convention the bird-leader said, “Guys, the trees are getting farther apart. We have to fly so far, and it’s tiring! I say let’s switch to those new streamlined wings. All in favor?” Again, think of the bush. The change observed in the birds’ wings took place over the last century; it’s not the bush growing, it’s the gardener trimming.

As another example of this aspect of evolution, consider Thoroughbred racing. The Kentucky Derby has been run at one and a quarter miles for over a hundred years. There is tremendous prestige, not to mention money, involved in producing the fastest horses, and breeders have worked very hard over the last century to improve their mounts’ times. Yet the average time of the last ten winners of the Derby is less than a 6% improvement on the time of the first ten winners. Even that overstates the situation, since training methods and riding techniques have presumably improved significantly over that time span as well. The reason for this modest improvement is simple: you can’t trim the bush taller. If you could, horses would be running the Derby at sixty miles per hour by now.

So what’s almost certainly happening with the birds is that previously there was some amount of genetic diversity in the shape of the birds’ wings. This may or may not have manifested in actual variations in the birds’ wing shapes; it’s possible for significant genetic variation to hide. As a gross simplification, one bird might have gene variations A1, B1, and C1. A1 contributes to more pointed wings, but only when accompanied by B3 and C2. Another bird might have A2, B3, and C3. If the two birds mate, none of their offspring will have more pointed wings because they all have either C1 or C3. Even if one of their offspring has A1, B3, and C3, it might then go on to mate with another bird that has A2, B1, and C1, and produce offspring that have A1, B1, and C1, putting us back at the start.

But some subset of the birds have A1, B3, and C2, and thus have more pointed wings. It doesn’t matter much how many of them there are, or even if any of them exist in a particular generation of birds; we have a century to work with here, and about a hundred generations of birds. As long as somewhere along the way A1, B3, and C2 show up and prove beneficial, we’re set. As we trimmed the forests, the bird population declined, and those with A1, B3, and C2 didn’t decline as much. They were better suited to the new environment, where before they were just average among the population. As birds without A1, B3, and C2 failed to compete as well and died off, the percentage of birds with more pointed wings went up: evolution happened.

The more harsh the environment is to the bird status quo, the faster this die-off and re-jiggering of the genetic population happens. The birds are “rapidly evolving,” but only in the sense of the herd being rapidly thinned. As another example, consider if we lined up every human being on the planet and killed off all of them who couldn’t run a mile in six minutes. We’d be left with a much smaller, much fitter population. But if we killed off everyone who couldn’t run a mile in three minutes, we’d be extinct. Doing it in stages wouldn’t help much. If we started with six minutes, and every ten years lowered the limit by ten seconds, we might find in 150 years that there were a number of people who could run sub-3:30 miles, but the human race would be only a few years away from extinction as the required time continued to drop. Again, you can’t trim the bush taller.

“Evolving” is a transitive verb

While it’s not technically wrong to say the birds are rapidly evolving, it’s more accurate and less prone to misunderstanding to say that we are rapidly evolving the birds. We have a history of doing this, and not just recently: we evolved dogs from wolves, we evolved cattle from aurochs (which we then eradicated), and the list goes on and on.

So don’t say that the birds are rapidly evolving. They aren’t hurrying ahead of us, morphing their genes to stay viable as we remake their world. We are changing their environment, and those least suited to the new situation are dying off. To paraphrase Darwin, the fittest birds are surviving, and they are surviving us.


A note about the use of the term “gardener”

In most instances where it appears in this entry, the “gardener” is us — mankind. In those instances where it isn’t, it is a metaphor for natural selection. Do not make the mistake of thinking this article supports intelligent design, or that I am in any way swayed by the temper tantrums put forth as arguments by its supporters. If you misquote me to support your falsehoods I will hunt you down and lecture you mercilessly.

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7 thoughts on “That’s not how evolution works

    1. gcanyon Post author

      (facepalm) I’m reminded of a Far Side comic that shows a flying saucer with stairs leading down from it. There are two aliens at the bottom of the stairs and people looking on, and one of the aliens is on the ground, obviously having fallen down the stairs. The other one is saying, “Well, so much for impressing them.” (or something like that, I haven’t seen the comic in fifteen years)

      Anyway, thanks for pointing out _my_ stupidity.

      Reply
  1. Rob Goldstein

    Hello, I wrote the original article on my website Conservation Maven and I suspect that Mother Jones used some of my language.

    First, I understand perfectly well the concept of natural selection spurring evolutionary change in response to stochastic events like increased forest fragmentation.

    There are two strong arguments for why I think I can write “birds changed wing shape” to reflect evolutionary change:

    1) By “change” I am saying “displayed change.” We use the term leaves changed color even though the leaves are not actively making a decision to modify their color. Rather we mean that the leaves are displaying a color change

    2) When people say “birds evolved pointier wings” or “birds changed their wing shape,” they aren’t referring to the actual organisms or population of organisms. Instead they are referring to the larger concept of “species” which includes the actual organisms, their functions, and their relationship to their environment. In the context of this bigger definition of species, I think it’s accurate when people say “birds evolved pointier wings”

    I think the Ecological Society of America agrees with me since they published the study and included the following language in the abstract:

    “songbirds evolved in response to recent changes in the amount of available habitat.”

    In the end, it’s just semantics. People express themselves differently.

    The problem I have with you is for using the word “Stupid.” Why throw around harsh language that’s going to ruin someone’s day just because you think they have their facts wrong.

    Reply
    1. gcanyon Post author

      First, thanks for taking the time to respond.

      1. Leaves do change color, birds don’t change wing shape. Further, I don’t think anyone is confused by the statement that leaves change color. No one would ascribe leaves changing colors to the tree’s desire to look pretty in the fall. On the other hand, I read an article recently that talked about why trees in North America chance to red, while trees in Europe apparently only change to yellow. The article described a pest that the trees in N.A. are subject to that isn’t as prevalent in Europe, and the red coloring is due to a chemical that helps protect the trees from the pest. If you said “The trees evolved to produce chemical X to protect themselves from Y,” that could be misleading, wouldn’t it?

      2. The opening sentence could be written as “A new study shows that over the past century the wing shape of some North American bird species has changed in response to the landscape being fragmented by clear-cutting.” That’s just a quick effort, but I think it’s clearer because a. it makes it obvious that it’s the wing shape of the species as a whole, not individual birds; b. it makes it clear that the change happened over the course of the century, not at some time within it; c. it states that it’s some bird species in particular in the study, not all bird species; d. it states that the change was in response to the clear-cutting, not just in parallel. It still doesn’t address the underlying issue of how evolution works, but I don’t see a good way to put that in a sentence. It would have to be addressed in the rest of the article.

      “I think the Ecological Society of America agrees with me…” Since you haven’t given any evidence of the expertise of the Ecological Society of America in evolution, or even science in general, this is exactly the fallacy I make fun of with the name of my blog. You did notice the name of my blog, right? 😉

      Saying “In the end, it’s just semantics,” is insulting to the study of semantics. Words have meaning, and can be clear or unclear, enlightening or misleading. There are many people who misunderstand evolution, and one of the common misconceptions is that animals as a species, or even individuals, evolve because they want to or need to, and that (for example) the giraffe could grow its long neck simply because the trees were taller. This idea needs to be corrected, and language such as that used in this article doesn’t help.

      By the tone of your writing it doesn’t seem your day was ruined by my use of the term “stupid.” This essay was labelled “rant” for a reason. If you’re offended, I apologize and suggest that the internet is a large place and it’s easy to avoid me. (but I still appreciate your taking the time to respond — thanks!)

      Reply
  2. Rob Goldstein

    Technically leaves don’t change their color. In most cases, environmental stressors induce the leaves the to stop producing chlorophyll which unmasks color in the leaves . To say that the leaves change their color might give someone the impression that the leaves are making decision to change their colors when in fact that is not how the process works. Yet no one cares when we say that leaves change color because it’s an easier way to communicate a more complex reality.

    In a similar vein, species change their wings over time because stochastic events (i.e. habitat loss) causes certain individuals with traits to die while others are able to live to pass on their genetic material. Similar to the leaves, the species is not actually changing its wing shape. Rather environmental stressors are inducing the change to happen in the species over time.

    As with the “stupid” comments, it didn’t ruin my day, but it irritated me – given the hard work I put into my site to provide a service to the conservation field, it’s frustrating to see people smear me as not understanding basic concepts of ecology when in fact it’s just a matter of a grammatical misunderstanding.

    Finally, the Ecological Society of America, founded in 1914 is the oldest and largest (I believe) professional society of ecologists in America. Their journal Ecology is among most important academic journals in the field. I agree that doesn’t make it the word of God, but I was just trying to point out that much smarter people than myself use similar language to describe the concept.

    Reply
  3. Rob Goldstein

    Another way of looking at is that certain birds are actually changing the wings of the species – i.e. the birds who are able to survive and reproduced despite habitat loss. They may not be making a conscious decision to change the wing shape of the species, but they’re working certainly work hard as hell to survive and spread their genes.

    Reply
  4. gcanyon Post author

    http://www.conservationmaven.com/frontpage/bird-wing-shape-changing-as-possible-adaptation-to-environme.html

    I read your article on the same subject, and I have to say that now I’m not sure why you disagree with me. The article in Mother Jones may be based on your blog entry, but yours is _far_ better written from the standpoint I’m complaining about. Your first line:

    “A newly published study in the journal Ecology finds evidence that the wing shape of birds in North America has changed over the last 100 years as an adaptation to the loss of forest habitat.”

    …is dramatically more clear than the Mother Jones article’s first line that I quoted. In particular, you say “the wing shape of birds in North America has changed over the last 100 years.” Compare that to “North American birds have changed the shape of their wings in the past century,” and I think my point is made. Further, you describe the change as an adaptation, where in Mother Jones it is simply described as coincident.

    In addition, in your article, you use the words “species” three times in your article, all three times in the context of the species changing or evolving. The Mother Jones article uses the word only once (apart from quotes) and then not in relation to change or evolution.

    In summary, your article is more clear and informative, and not misleading as the Mother Jones piece is. I would never have used the word “stupid” to describe your article, and in fact at the time I wrote my essay I didn’t know about you or your article, so obviously I didn’t intend to smear you.

    That said…

    You don’t see the difference between the individual leaves on a tree changing their color and the average wing shape of a bird species changing over time? As described at http://en.wikipedia.org/wiki/Autumn_leaf_color#Chlorophyll_and_the_green_color, the leaf acts in ways that eliminate chlorophyll. Further, as I alluded to above, the red pigment is actively produced by cells in the leaves. So yes, leaves _do_ change color. They may do it in response to external stimuli, but they do change. Individual birds on the other hand are not changing their wing shape in response to their environment; the average shape of the wings of a species change.

    Further, I’ve never heard anyone ascribe sentience to leaves because they change colors, while _many_ people misunderstand and misconstrue expressions related to lifeforms (animals in particular) changing in response to evolutionary pressure.

    Regarding the Ecological Society of America, again I point to the title of my blog. Appeal to Authority, or http://en.wikipedia.org/wiki/Argument_from_authority is the argument that something is true simply because someone smart or knowledgeable said it. I reject that, and the title of my blog is intended ironically.

    Finally, you say, “Rather environmental stressors are inducing the change to happen in the species over time.” This strays close to misinformation. Saying that stressors induce a change implies either that they can make the change happen themselves, or perhaps makes the assumption that species have the inherent ability to change and the stressors have the ability to force the species to undertake the change. At the risk of being repetitive I will say that you can’t trim the bush taller. If natural variation hasn’t produced an individual with a particular characteristic, a species cannot evolve to have that characteristic no matter how beneficial it might be.

    Repeatedly people hear that we are breeding superbugs by overuse of antibiotics, that animals humans hunt are evolving to be smaller and breed sooner, and that they are evolving “faster” than other species. Statements like this imply that evolutionary change is something animals can do at will, when this is completely false. As someone interested in conservation, I assume you understand that the result of more selection pressure is (beyond a certain point) not faster evolution, but extinction. A wider understanding of this fact can only help your cause.

    Reply

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