Genetic Drift for dummies

How, when and where does drift happen?

I don’t know much about the Kahn Academy but their Wikipedia entry suggests they don’t have any political or religious axe to grind. Here is their description of genetic drift:

Genetic drift is change in allele frequencies in a population from generation to generation that occurs due to chance events. To be more exact, genetic drift is change due to “sampling error” in selecting the alleles for the next generation from the gene pool of the current generation. Although genetic drift happens in populations of all sizes, its effects tend to be stronger in small populations.

So drift happens all the time but its effects are more noticeable in small populations and two ways that populations become small have their own names: bottleneck effect and founder effect. Bottlenecks occur when some catastrophe reduces a population to a small number of individuals, a partial extinction. The result is that individuals carrying alleles (alternative copies of genes) occurring at low frequency may be eliminated altogether or so reduced in number that those alleles are lost for good in the next generation or two and thus genetic diversity is lost. Founder effect is where a small sample of a large population (or the extreme example of a single individual) becomes permanently isolated from the main population, such as by being transported to a new environment devoid of the main population. Again, alleles present at a low level can be lost completely in the isolated small population.

I don’t think there is controversy that genetic drift is a real phenomenon. What I have had difficulty in seeing is how genetic drift contributes to evolution as a whole. Being, by definition, a random process and one that, in small populations, reduces diversity, I think I’m correct that drift does not contribute to selective adaptation. But perhaps, where small subsets of populations go through a bottleneck, it creates a consequent springboard for subsequent adaptation in the surviving population.

But I place myself in the dummy category regarding drift and appreciate any corrections as necessary in my text above. This isn’t the first time I’ve expressed skepticism as to the importance that drift should be accorded so my apologies for being a slow learner and I look forward to input from those more informed than me.

I should credit Berkeley University University of California, Berkeley for the diagram above.

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165 thoughts on “Genetic Drift for dummies

  1. I think I am starting to get it.

    And I agree with Flint. Gassing 6 million Jewish men, women, and children was “misguided”. I think it was a bad idea.

    Very misguided. Tasteless.

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  2. phoodoo:
    I think I am starting to get it.

    And I agree with Flint.Gassing 6 million Jewish men, women, and children was “misguided”.I think it was a bad idea.

    Very misguided. Tasteless.

    Indeed. But not quite as misguided as being a bit on the ‘vengeful’ side. God: do as I say, not as I do.

    I’m off to smite someone.

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  3. phoodoo:
    Alan Fox, Sort of like exterminating the Jews is the niche?

    Not really. If a sub-population were exposed to some effect that, over generations, culled individuals selectively, for example blue-eyed individuals were targetted, in following generations the alleles for blue-eyes would be fewer and eventually lost.

    The Nazis were engaged in genocide, not evolution.

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  4. phoodoo: You haven’t made the case for there being a difference.

    Narrator: phoodoo hoped nobody would mention the global fludd. They did.

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  5. phoodoo: Sort of like exterminating the Jews is the niche?

    Ahh dear phoodoo is still endlessly obsessed with some presumed value judgement regardeing the concept of fitness. It is as if phoodoo has implicitly bought in to the nauralistic fallacy. If something happens in nature, or is a natural process then it appears phoodoo thinks that is how it should be, or that makes it right, or morally justified. Phoodoo’s moral philosophy is of course, then, very confused. He appears to have effectively adopted eugenics rationalizations.

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  6. Rumraket: Ahh dear phoodoo is still endlessly obsessed with some presumed value judgement regardeing the concept of fitness

    So you mean you are against the “value judgement” that exterminating Jews in WWII was misguided.

    Who are we to judge you might say. Well, to each his own. How about uncouth, would you go that far? Unoriginal?

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  7. phoodoo: So you mean you are against the “value judgement” that exterminating Jews in WWII was misguided.

    There’s a difference between saying a value judgement was misguided, and saying it wasn’t a value judgment. I find myself in disagreement with many of your opinions, but despite my disagreement, they remain opinions.

    I agree with the value judgment that exterminating Jews (or discriminating against any minority) is misguided, but clearly others don’t consider it misguided, and are willing to organize, march, and chant in vociferous favor of discriminating against those not like themselves.

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  8. Am I alone in thinking that phoodoo is trying to imply that people who talk about natural selection are trying to normalize the Holocaust? Is it time for Godwin’s Law?

    +3
  9. Joe Felsenstein:
    Am I alone in thinking that phoodoo is trying to imply that people who talk about natural selection are trying to normalize the Holocaust?Is it time for Godwin’s Law?

    I am not making that argument at all. I am making the argument that by the definitions of evolution and fitness by the likes of the proponents here , there is no means for distinguishing between drift and selection. Furthermore there is no means for distinguishing between racist terrorist killings and a mutation for cystic fibrosis as a factor for survival. And still further the whole notion of a niche is complete bonkers because everything is the niche. If a nuclear bomb wiped Poland off the map, then the Polish genes were of low fitness because of their particular niche.

    Genetic drift, gene flow, mutation pressure, and natural selection, epigenetics, inherited methylation patterns, recombination, plasticity, niche constuction, adaptation, natural genetic engineering, rapid neo-darwinain evolution, reciprocal causation, constructive development, inclusive inheritance, developmental bias,neutral fitness theory, inclusive fitness theory, Ornstein-Uhlenbeck evolution, convergent evolution, divergent evolution, parallel evolution, coevolution, Allopatric speciation, Peripatric speciation, Parapatric speciation, Sympatric speciation,..The modern theory of evolution is a giant wok of wonkiness.

    This difference in how development is conceived strongly affects evolutionary interpretations. Readers that view developmental plasticity as programed by genetically specified switches or reaction norms, pre-screened by prior selection, would find it hard to envisage how responses to the environment can be the starting point for evolutionary change as plasticity-led evolution then reduces to selection on genetic variation. Conversely, if, for instance, as a result of exploratory processes, development is constructive and open-ended, entirely new functional phenotypes may be able to emerge with little or no initial genetic modification, yet nonetheless generate critical new raw material for subsequent bouts of selection (e.g. [30]). In such cases, the genetically specified reaction-norm approach is limited, because phenotypic variation results from ontogenetic selective processes, rather than genes, responding to environmental variation.

    *

    *source-as if it matters.

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  10. Hey. Joe never replied to my reply to his somewhat off broadway point.r Then for some reason ancient history from the old wars came up. There has been more wars and slaughter since folks. Anyways.
    I suspect mutations are not errors but the essence for biological bodyplan changes in a system. What we see as mutations is just a end of a spectrum or hair trigger that allows them as errors.
    yet regardless. Why should these errors , thus drift, ever create new populations? So who proves genetic drift is a real thing? Today or in the past WHERE has drift actiually truly brought evolution? Is it really just only a line of reasoning that errors would create new bodyplans? Say it ain’t so.

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  11. DNA_Jock,

    Lots of good stuff there. One point that deserves emphasizing is reciprocal causation. I’ve long thought that A causes B is simplistic and often misleading. A and B interact and both are changed.

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  12. phoodoo: And still further the whole notion of a niche is complete bonkers because everything is the niche.

    Well, anything and everything that affects the viability of a population of organisms is part of the niche. Essentially, it’s a very simple idea.

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  13. phoodoo: I am not making that argument at all. I am making the argument that by the definitions of evolution and fitness by the likes of the proponents here , there is no means for distinguishing between drift and selection.

    LOL. Ahh yes of course, that’s what you were saying here:

    Phoodoo:“Are you saying that Jews during WWII were less fit, and that is why their numbers dwindled?”

    Or

    Phoodoo:“Sort of like exterminating the Jews is the niche?”

    Clearly that’s all about distinguishing deaths due to instances of selection from deaths due to random sampling. No attempted “But the Nazis” smear there at all, nope. No siree!

    +1
  14. Alan Fox: Have you heard the story of Br’er Rabbit and the briar patch?

    Yup I have herd of brother rabbit adventures but nope this it ain’t it.

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  15. Robert Byers,
    I was hinting at an explanation for why your comments don’t get the attention you may think they deserve. There’s no benefit in engaging with you.

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  16. Alan Fox,

    A pop-up book with colorful pictures of gas chambers perhaps? Links to World War 2 for dummies websites? A catchy nursery rhyme?

    I hate you
    You hate me
    Let’s go over and kill Barney…And Morty too!

    With a 2 by 4
    And Barney’s no more (and Morty too)
    No more stupid deynasor (דיינאַסאָר).

    I hate you, you hate me….

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  17. phoodoo: A pop-up book with colorful pictures of gas chambers perhaps? Links to World War 2 for dummies websites? A catchy nursery rhyme?

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  18. phoodoo,

    Seems like the theme of evolution brings out the worst of you phoodoo. For the sake of your mental health, I’d advice you to avoid the theme altogether and never visit this site again.

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  19. Entropy,

    Well then do you have some more books on the Theory of Evolution I can read up on?

    I have already read the

    The Diary of Anne Frank

    and have ordered

    Mengele-The Complete Story

    based on some suggestions by Alan and Flint about niche construction.

    The Mengele book should be most useful, it is written by famous “Skeptic”Gerald Posner. He hates conspiracy theories except when he is writing about them. Skeptic books are always fun reads.

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  20. Alan Fox:
    Robert Byers,
    I was hinting at an explanation for why your comments don’t get the attention you may think they deserve. There’s no benefit in engaging with you.

    I always got the attention i wanted. it was just to this subject and why conversation stops. If there is no benifit in engaging with me then this must mean there is with everyone else or most of some or somebody. Maybe a chart should be kept eh!

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  21. Alan Fox seems to think there is a scientific way to distinguish “a chance event” from “a non-chance event.”

    I guess he must be an ID proponent!

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  22. Mung: I guess he must be an ID proponent!

    Nope.

    Do ID proponents have a method for distinguishing between random events from “guided” events?

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  23. phoodoo,
    Hitler and the third Reich Nazis were terrible people. I still fail to see any particular connection to genetic drift.

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  24. Alan Fox: Nope.

    Do ID proponents have a method for distinguishing between random events from “guided” events?

    Do ID theorists have a position on whether the process of natural selection is “chance” or “necessity”? On whether genetic drift is “chance”? Is “random”? For people who use these terms like “chance”, “necessity” and “random” a lot and consider their understanding of these issues to be good, and who are talking about their implications for biology, they certainly leave us mystified as to exactly how they apply to evolutionary processes.

    +3
  25. Oops. Managed to mash up “distinguish between A and B” with “distinguish A from B”

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  26. Alan Fox: Hitler and the third Reich Nazis were terrible people. I still fail to see any particular connection to genetic drift.

    I guess that when a meticulously planned event turns out to be an appalling smear on history, it doesn’t count as ‘designed’ anymore.

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  27. Corneel: I guess that when a meticulously planned event turns out to be an appalling smear on history, it doesn’t count as ‘designed’ anymore.

    Appalling? What do you mean by appalling? That sounds like a value judgement. Misguided perhaps, but how can natural selection be appalling?

    But maybe I am even being a little presumptuous. The loss of the Jewish gene during WWII may not have been natural selection at all. It could have just been the result of random genetic drift. Because there really is no way to know one from the other.

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  28. phoodoo: But maybe I am even being a little presumptuous. The loss of the Jewish gene during WWII may not have been natural selection at all. It could have just been the result of random genetic drift. Because there really is no way to know one from the other.

    How odd that you are suddenly incapable of recognizing a free will choice.

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  29. phoodoo:
    Well then do you have some more books on the Theory of Evolution I can read up on?

    I think you should learn to read:

    Entropy:
    Seems like the theme of evolution brings out the worst of you phoodoo. For the sake of your mental health, I’d advice you to avoid the theme altogether and never visit this site again.

    Is that clear for you now?

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  30. phoodoo: How odd that you suddenly recognize free will.

    What is a decision in phodoo world? We never did find out….

    phoodoo expresses that it is odd that someone now recognizes free will but has failed to detail how he himself recognises it.

    phoodoo: Just another name for the niche according to your side.

    Your ‘side’ says it all really. There’s only one reality, one set of facts.

    So genetic drift is nonsense because the Nazis? I guess it makes about as much sense as phoodoo ever has or will ever make.

    Luckily they pay him so well I guess. When you are the best in the world at your job, that’s a given.

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  31. phoodoo: How odd that you suddenly recognize free will.

    How odd that you suddenly acknowledge natural selection and genetic drift.

    Is somebody keeping score?

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  32. Corneel: I guess that when a meticulously planned event turns out to be an appalling smear on history, it doesn’t count as ‘designed’ anymore.

    Appalling? What do you mean by appalling? That sounds like a value judgement.

    Words like appalled, horrified, repelled generally refer to the emotional reaction of reasonable humans on learning of some particular atrocity by other humans.

    Misguided perhaps, but how can natural selection be appalling?

    Well, it can’t of course. Selection is a process, not a human.

    But maybe I am even being a little presumptuous.

    Difficult to tell what your objective in commenting here is but whatever.

    The loss of the Jewish gene…

    You should have learned by now that there is no one-to-one relationship between genotype and phenotype. You should also be aware that suggesting that Jewishness is genetic is racist in my view. The Skeptical Zone does not tolerate racist views.

    …during WWII may not have been natural selection at all. It could have just been the result of random genetic drift. Because there really is no way to know one from the other.

    Drivel that does not rise to the level of requiring refutation.

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  33. Alan Fox: You should also be aware that suggesting that Jewishness is genetic is racist in my view. The Skeptical Zone does not tolerate racist views.

    Oh, you are so funny Alan.

    But hey, this is great news. Since you are NOW saying that Jewishness is simply a religious choice and NOT a race, making fun of Jews would not be racist! Of course , because of your autism perhaps, you have zero memory of claiming EXACTLY the opposite when you tried to ban me earlier. Go back and look for yourself.

    But hey, today Jewishness is a choice. Thus its ok to make fun of Jews here the same way that your side makes fun of Christians and Creationists and Idists…

    Oy vey, this is great Alan. Have I got some funny Jewish jokes for you Alan, you are going to love them! Then again, you won’t get them, but still….

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  34. phoodoo: Since you are NOW saying that Jewishness is simply a religious choice and NOT a race, making fun of Jews would not be racist!

    Nope. Jewishness is both an ethnicity and a religion. If you want to make jokes about the oddness of the Jewish religion, or indeed about any religion, or indeed about atheism, feel free. If you want to make racial slurs about people of a particular ethnicity, do it elsewhere.

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  35. Alan Fox: Jewishness is both an ethnicity and a religion

    Alan Fox: You should also be aware that suggesting that Jewishness is genetic is racist in my view.

    Do you see why I believe you could be autistic ?

    Or just full of shit?

    Wait, wait, you are are racist! I get it! Whew, I was getting worried about you.

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  36. phoodoo

    You’re making no sense to me, phoodoo, and I don’t think it’s all my fault. What is it that I’ve done or said that suggests to you I’m racist?

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  37. Alan Fox,

    Alan Fox: Jewishness is both an ethnicity and a religion

    Alan Fox: You should also be aware that suggesting that Jewishness is genetic is racist in my view.

    Are you now going to say that ethnicity isn’t genetic?

    Its not me who has to do the work of making things clearer for you Alan.

    If you really can’t see the hypocrisy of those two statements, made only a short time apart, please ask someone who suffers fools better than I to explain.

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  38. phoodoo: Are you now going to say that ethnicity isn’t genetic?

    Yes. Ethnicity does not depend on genetic make up but on the culture you you absorb and are immersed in. There are certainly genetic markers indicating biological ancestry.

    If you are to it to call me a racist, it would seem reasonable to support this assertion.

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