5 ms·

Urban Evolution: How Species Adapt, or Don't, to City Living

28 points by Thevet 10y ago

itchyjunk 10y ago
"The moths evolved to become dark in order to match the background of these trees." "Those guppies evolved to be very colorful, over the course of just two years." "Over ten years they evolved significantly shorter legs." Remember, the variation already existed. There were already white and dark months in the population and natural selection caused increase or decrease in the ratios. The black moth did not evolve into white. The variation for short and long legs already existed. Short legs probably increased reproductive fitness in once case and not the other. Causing the number of individuals with certain trait to increase or decrease. My professor has repeated this the entire semester and she wants us to never forget that mutation is the only source of variation. If the variation is not already present, natural selection cannot trigger it. This is how some species go extinct. Natural selection is one source of evolution. Also, distinction between micro vs macro evolution is important here. [0] "But there's no reason to believe this. Why shouldn't they be adapting to our conditions just like any other evolutionary situation?" Because natural selection doesn't cause variation. Mutation is the only source of variation. Variation must already exist in a population for natural selection to work on it. "What she found was that in each case they had changed. The lizards in the city had evolved longer legs—presumably useful for hanging onto broad surfaces, like walls—and they had evolved bigger toe pads—again, presumably to hang on to the smooth surfaces in cities. " Giraffe's neck get longer with usage is a Lamarackian theory which is an outdate model because we know only changes in the sex genes are passed on to offspring. [1] "Evolutionary biologists have become very interested in recent years in a higher-level analog of this, and that is the mixing of different species—hybridization—when two different species interbreed and are able to successfully reproduce." Depends on your definition of species, there are many. [2] The biological definition is one where if they fail to see each other as potential mate naturally and produce sterile offspring, they are different species. So I am not sure which of the 13ish popular definition I am supposed to apply to this. And genetic definition always considered more variations to be good. So that one won't work here either. "When wolves were around, coyotes were small. But, you get rid of the wolf, suddenly, there's this great opportunity for coyotes to evolve to get bigger and eat the bigger food that the wolves aren't taking, such as deer." There is no selective pressure so both big and small coyotes would increase in number. I know where this is from though, we watched the video in class. It's called "How wolves change the river."[3]. It's really good, please watch it. "Are they just mutations for larger size that then get taken advantage of by natural selection? That can happen, it might play a role, but it seems more likely in the case of a coyote that it's the result of hybridization" So the author is aware of the concepts but it just brushing them off? "Think about weightlifters, for example. If you spend your life lifting weights, you'll develop very big muscles and thick bones. But that is not a genetic change. You have not evolved. " Correct, it means that variation "genotype[4]" is already present. "Those differences will not be passed on to your offspring." Incorrect. there is a change that the genes that allowed for larger muscles in you will be passed on. Just the "phenotype" won't pass. The kid wont be born with big muscles, but like you, if he exercises, he might get similar muscle. I don't see citation for any of the claims on the articles. If I missed it, I apologize. I am not an expert and these are just my opinions based on my very limited understanding on the subject matter. Feel free to correct me. ------------- [0] http://evolution.berkeley.edu/evolibrary/article/evoscales_01 http://evolution.berkeley.edu/evolibrary/article/evoscales_0... [1] http://natureinstitute.org/pub/ic/ic10/giraffe.htm http://natureinstitute.org/pub/ic/ic10/giraffe.htm [2] http://evolution.berkeley.edu/evolibrary/article/evo_41 http://evolution.berkeley.edu/evolibrary/article/evo_41 [3] https://www.youtube.com/watch?v=ysa5OBhXz-Q https://www.youtube.com/watch?v=ysa5OBhXz-Q [4] https://en.wikipedia.org/wiki/Genotype https://en.wikipedia.org/wiki/Genotype Edit: Added white space for clarity as suggested.
- imartin2k 10y ago
  May I ask: If you are not an expert and only have opinions and "very limited understanding on the subject", and if we consider this subject to be extremely complicated and research-heavy, why do you then put so much effort in writing a lengthy comment and what's the value of it for others? Or are you actually an expert and were just trying to be humble?
  - itchyjunk 10y ago
    I came across evolutionary theory in an Anthropology class. I am not asking anyone to take my word for it, but maybe at least inspire some to double check the information provided. I get a lot out of HN comments and this is just my attempt to give back.
    - kwhitefoot 10y ago
      Having taken, and paid attention to, an anthropology class makes you considerable more expert than most people, including I think most of us on HN. I'm not totally familiar with US terminology, I presume this means a course in anthropology, perhaps lasting one term or semester? But, "came across", sounds a bit accidental. Isn't evolutionary theory central to anthropology? I'm just an interested layman in this field (with a book shelf full of Richard Dawkins, Charles Darwin, Stephen J. Gould, Daniel Dennett, Steve Jones, as well as sundry textbooks).
      - itchyjunk 10y ago
        Yes, the course is called Introduction to Physical Anthropology (1020). It's a 1 semester 3 credit class. Yup, most of the course introduced what evolution is, how it's studied, variation, macro-micro evolution etc. It than applies this to living primates and Hominin remains. I phrased the way I did because our professor said that other than some fundamentals, no one agrees completely on anything and there is a lot of school of thought. So the author might subscribe to some other school of thought, I wouldn't know. But it contradicts a lot with what I was taught so I felt I should point it out.
kwhitefoot 10y ago
I think that was a rather confusingly written article. It uses the word evolution in several different senses which means that it is hard to see if the writer really understands the subject. Yet, he is a professor at Harvard so I think it is safe to assume that he really does understand it. The problem is that a careless reader could quite easily skim the article and conclude that the moths, for instance, had undergone genetic changes as a result of the environmental changes when all that had happened was that the proportion of the population that was darkly pigmented had increased, presumably because predators were able to see the lighter variants more easily. If it had continued long enough it is quite possible that this variation in frequency could have become fixed by driving the light coloured variants out entirely. But evolution, as I understand it anyway, is the combination of mutation plus the fixation of that mutation through differential survival; that is we have to include the origin of the light and dark varieties as well as the differential survival of them. Lastly this: > The moths evolved to become dark in order to match the background of these trees. That's backwards. The dark variants already matched the trees, selection pressure (differential predation) caused that variant to become more frequent in the population when the environment changed. It would make sense to say: The moth population evolved to become dark because they matched the background of these trees thus resulting in fewer of them being eaten by birds. But even that is open to misinterpretation because not everyone will distinguish between the moths and the population. There is no shortage of well written works on this subject so it is a pity to see a confusing one mentioned on HN. I personally recommend Almost Like a Whale: The 'Origin of Species' Updated by Steve Jones for a popular rendering and The Blind Watchmaker and The Extended Phenotype by Richard Dawkins for those wanting a more technical explanation. A disclaimer: unlike itchyjunk I really am not an expert, just a moderately well read engineer with physics degree.

28 points by Thevet 10y ago

"The moths evolved to become dark in order to match the background of these trees." "Those guppies evolved to be very colorful, over the course of just two years." "Over ten years they evolved significantly shorter legs." Remember, the variation already existed. There were already white and dark months in the population and natural selection caused increase or decrease in the ratios. The black moth did not evolve into white. The variation for short and long legs already existed. Short legs probably increased reproductive fitness in once case and not the other. Causing the number of individuals with certain trait to increase or decrease. My professor has repeated this the entire semester and she wants us to never forget that mutation is the only source of variation. If the variation is not already present, natural selection cannot trigger it. This is how some species go extinct. Natural selection is one source of evolution. Also, distinction between micro vs macro evolution is important here. [0] "But there's no reason to believe this. Why shouldn't they be adapting to our conditions just like any other evolutionary situation?" Because natural selection doesn't cause variation. Mutation is the only source of variation. Variation must already exist in a population for natural selection to work on it. "What she found was that in each case they had changed. The lizards in the city had evolved longer legs—presumably useful for hanging onto broad surfaces, like walls—and they had evolved bigger toe pads—again, presumably to hang on to the smooth surfaces in cities. " Giraffe's neck get longer with usage is a Lamarackian theory which is an outdate model because we know only changes in the sex genes are passed on to offspring. [1] "Evolutionary biologists have become very interested in recent years in a higher-level analog of this, and that is the mixing of different species—hybridization—when two different species interbreed and are able to successfully reproduce." Depends on your definition of species, there are many. [2] The biological definition is one where if they fail to see each other as potential mate naturally and produce sterile offspring, they are different species. So I am not sure which of the 13ish popular definition I am supposed to apply to this. And genetic definition always considered more variations to be good. So that one won't work here either. "When wolves were around, coyotes were small. But, you get rid of the wolf, suddenly, there's this great opportunity for coyotes to evolve to get bigger and eat the bigger food that the wolves aren't taking, such as deer." There is no selective pressure so both big and small coyotes would increase in number. I know where this is from though, we watched the video in class. It's called "How wolves change the river."[3]. It's really good, please watch it. "Are they just mutations for larger size that then get taken advantage of by natural selection? That can happen, it might play a role, but it seems more likely in the case of a coyote that it's the result of hybridization" So the author is aware of the concepts but it just brushing them off? "Think about weightlifters, for example. If you spend your life lifting weights, you'll develop very big muscles and thick bones. But that is not a genetic change. You have not evolved. " Correct, it means that variation "genotype[4]" is already present. "Those differences will not be passed on to your offspring." Incorrect. there is a change that the genes that allowed for larger muscles in you will be passed on. Just the "phenotype" won't pass. The kid wont be born with big muscles, but like you, if he exercises, he might get similar muscle. I don't see citation for any of the claims on the articles. If I missed it, I apologize. I am not an expert and these are just my opinions based on my very limited understanding on the subject matter. Feel free to correct me. ------------- [0] http://evolution.berkeley.edu/evolibrary/article/evoscales_01 http://evolution.berkeley.edu/evolibrary/article/evoscales_0... [1] http://natureinstitute.org/pub/ic/ic10/giraffe.htm http://natureinstitute.org/pub/ic/ic10/giraffe.htm [2] http://evolution.berkeley.edu/evolibrary/article/evo_41 http://evolution.berkeley.edu/evolibrary/article/evo_41 [3] https://www.youtube.com/watch?v=ysa5OBhXz-Q https://www.youtube.com/watch?v=ysa5OBhXz-Q [4] https://en.wikipedia.org/wiki/Genotype https://en.wikipedia.org/wiki/Genotype Edit: Added white space for clarity as suggested.

imartin2k 10y ago
May I ask: If you are not an expert and only have opinions and "very limited understanding on the subject", and if we consider this subject to be extremely complicated and research-heavy, why do you then put so much effort in writing a lengthy comment and what's the value of it for others? Or are you actually an expert and were just trying to be humble?
- itchyjunk 10y ago
  I came across evolutionary theory in an Anthropology class. I am not asking anyone to take my word for it, but maybe at least inspire some to double check the information provided. I get a lot out of HN comments and this is just my attempt to give back.
  - kwhitefoot 10y ago
    Having taken, and paid attention to, an anthropology class makes you considerable more expert than most people, including I think most of us on HN. I'm not totally familiar with US terminology, I presume this means a course in anthropology, perhaps lasting one term or semester? But, "came across", sounds a bit accidental. Isn't evolutionary theory central to anthropology? I'm just an interested layman in this field (with a book shelf full of Richard Dawkins, Charles Darwin, Stephen J. Gould, Daniel Dennett, Steve Jones, as well as sundry textbooks).
    - itchyjunk 10y ago
      Yes, the course is called Introduction to Physical Anthropology (1020). It's a 1 semester 3 credit class. Yup, most of the course introduced what evolution is, how it's studied, variation, macro-micro evolution etc. It than applies this to living primates and Hominin remains. I phrased the way I did because our professor said that other than some fundamentals, no one agrees completely on anything and there is a lot of school of thought. So the author might subscribe to some other school of thought, I wouldn't know. But it contradicts a lot with what I was taught so I felt I should point it out.

kwhitefoot 10y ago

I think that was a rather confusingly written article. It uses the word evolution in several different senses which means that it is hard to see if the writer really understands the subject. Yet, he is a professor at Harvard so I think it is safe to assume that he really does understand it. The problem is that a careless reader could quite easily skim the article and conclude that the moths, for instance, had undergone genetic changes as a result of the environmental changes when all that had happened was that the proportion of the population that was darkly pigmented had increased, presumably because predators were able to see the lighter variants more easily. If it had continued long enough it is quite possible that this variation in frequency could have become fixed by driving the light coloured variants out entirely. But evolution, as I understand it anyway, is the combination of mutation plus the fixation of that mutation through differential survival; that is we have to include the origin of the light and dark varieties as well as the differential survival of them. Lastly this: > The moths evolved to become dark in order to match the background of these trees. That's backwards. The dark variants already matched the trees, selection pressure (differential predation) caused that variant to become more frequent in the population when the environment changed. It would make sense to say: The moth population evolved to become dark because they matched the background of these trees thus resulting in fewer of them being eaten by birds. But even that is open to misinterpretation because not everyone will distinguish between the moths and the population. There is no shortage of well written works on this subject so it is a pity to see a confusing one mentioned on HN. I personally recommend Almost Like a Whale: The 'Origin of Species' Updated by Steve Jones for a popular rendering and The Blind Watchmaker and The Extended Phenotype by Richard Dawkins for those wanting a more technical explanation. A disclaimer: unlike itchyjunk I really am not an expert, just a moderately well read engineer with physics degree.