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My understanding is that the possible mechanisms of evolution are:

  • Environmental changes
  • Cultural/mating preferences
  • Population Immigration
  • Genetic Mutation

Am I missing anything? I've heard that population shifts within a existing populaces will effect evolution, but imagining the most simplicity scenario, it's hard to see why the would make a difference.

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blunders
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    It's not really clear what 'factors of evolution' you are referring to... there are many factors that play a role in evolution - availability of nutrients, availability of reproductive partners, space,... Could you clarify a bit what kind of factors you mean? – Armatus May 22 '12 at 20:13
  • @Armatus: "availability of nutrients" would be an environmental change. I'm not sure about "availability of reproductive partners", though I believe that if the availability partners was stable, it would not be a factor, and I already stated in the question that it is unclear to me if "population shifts" beyond population immigration play any significant role. – blunders May 22 '12 at 20:21
  • @Armatus: My list is based on this video, the "Five Fingers of Evolution" - though I've edited it's meaning to make more sense to me; for example, "Environmental changes" I believe are called adaption, which to me is less clear the saying the changes are a result of the environment changing. If it's still not clear what I mean, please attempt to be more description on were exactly things are clear, and unclear. Thanks! – blunders May 22 '12 at 20:35
  • I'll have an attempt at an answer in a moment :) – Armatus May 22 '12 at 20:39
  • If I understand right, it may be good to change your question to "What mechanisms can cause evolution" and also quote that definition - that evolution is merely any change in the gene pool. On the other hand, you are answering your own question - it's all in that clip which you linked. Maybe you could include that in the question and more specifically ask something you don't understand in the video? – Armatus May 22 '12 at 20:58
  • +1 @Armatus: Yes, mechanisms is more clear, I've updated the question. Also, I agree that evolution is genetic change, though currently genetic change unless previously tied to a known trait is meaningless. – blunders May 22 '12 at 22:16
  • @Armatus: As for the video, I found the use of 'mating' to mean non-genetic bias, not genetic, which to mean upon reflection seems a likely mechanism, and would be it's own; meaning there's a delay in the genetic mating bias generational stabilization of a genetic mating bias. Population shift role in evolution appear unimportant if selection within the shift is random; non-random shifts would another mechanism. – blunders May 22 '12 at 22:16
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    I've changed the question title slightly from active to passive phrasing. The reason being is that not all of these directly affect changes in the gene pool (ie, environmental factors). Furthermore, evolution can be semantically argued to have differing definitions. –  May 23 '12 at 00:06
  • +1 @leonardo: Thanks, so are you saying environmental changes are not the mechanisms of change when the only change done within lab setting is within the environmental factors, and a minority genetic trait within the genome of a populous shifts due to the change? If so, then what is the mechanism in those circumstances? As for the meaning of evolution, "Evolution is any change across successive generations in the inherited characteristics of biological populations." – blunders May 23 '12 at 00:15
  • @blunders - I would put that definition in your question so that we have a standard definition (it can be mis-used in popular speech). I'm saying that generally, environmental factors are not physically causing a change to the genetic material (except for mutagens, carcinogens, teratogens) and the organism's adaptation to this change is what is causing heritable changes to its genetic material. Environmental factors change dynamically and passively, but it is the organism that is dynamically reacting. You wouldn't say that weather or food edited your genome. A small point of semantics. –  May 23 '12 at 00:33
  • @leonardo: Thanks, I've updated the question attempt to pull content from the comments into the body of the question. So, yes, in fact I would say that environmental factors "edited" the genome of our species, and most species for that matter. Species don't make up genes to adapt to change, genetic traits either becomes more or less used. Just because environmental change dynamically and passively, does not mean environmental changes are not the one to the mechanisms of change in my opinion. – blunders May 23 '12 at 00:48
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    The first version of the question was vastly superior. In the current form, it’s much too long, needlessly detailed, contains errors, and no longer is a question. I’d suggest reverting to something much closer to the original form. – Konrad Rudolph May 23 '12 at 09:22
  • @blunders - You're sort of right. Let's take climate as an example. The organism certainly senses the climate. Among the population, there are genetic variations that make up the collective gene pool. The error in your logic is assuming that there exists a gene and that provides adaptation to the climate, but that it is currently "switched off", and when a specific climate is sensed, turns the gene "on". This is incorrect because it is impossible for the gene pool to hold potentially adaptive genes for all scenarios of climate. –  May 23 '12 at 23:53
  • The climate is a possible stimulus, to which invidual species, with their individual genetic differences, stand a better or worse chance to exist in that weather. The better suited organisms (better adapted) survive and bias the gene pool with their offspring. These changes build until new features or traits are acquired. The important thing here is that climate is independent of the organism, and is independent of the gene pool, but it provides a stimulus to which the organism can respond. –  May 23 '12 at 23:53
  • why would you find out more here than on wikipedia, which has 1000 lines on it, with all references. – bandybabboon Sep 18 '17 at 14:32

2 Answers2

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Evolution is defined as a change in the allele frequency of population through time. The Hardy-Weinberg model predicts that the allele frequency of a population will not change (i.e., evolution will not occur) if the following conditions are met:

  • no natural or sexual selection

  • no gene flow (immigration or emigration from the population)

  • no mutatation

  • no genetic drift (changes in allele frequency due to random events)

So we can conclude that if any of the above conditions are not met then there is a change in allele frequency and thus evolution, and thus that factor is the cause of evolution.

DQdlM
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  • +1 @DQdlM: Awesome! Knowing now that Hardy-Weinberg appears to be the source of the logic was a huge help, and you're answers was within my range of plain-English. Taking a step back from "bio-lingo", would it be correct to say that the "inputs" for natural selection are only mutation(s) and/or statistically significant changes in the way the organism interacts with the environment? Also, assuming mating was completely random, why would emigration affect evolution? Meaning it would appear that other conditional changes would be the source of the evolutionary change, not emigration. Thanks! – blunders May 23 '12 at 01:39
  • @blunders natural selection requires heritable variation and a survival or reproductive advantage based on that variation. The ultimate source of all variation is mutation but note that the thing that evolves is a population, so you can change the allele frequency by having individuals enter or leave a population. This would be an evolutionary event unto itself but would also potentially add more heritable variation that natural selection could act upon. – DQdlM May 23 '12 at 10:57
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    The answer is actually partially wrong. I agree that under all of the above conditions, no change in allele frequency can occur. However, this is true even if you drop the last condition (random mating). In absence of random mating (and in presence of the other conditions), genotype frequencies may change through time (and differ from Hardy-Weinberg's predictions) but allele frequencies would still remain constant. – Remi.b Jun 12 '16 at 23:25
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    @Remi.b thanks for your comments. I agree with your feedback so I have edited the answer in response. Thanks. – DQdlM Jun 13 '16 at 14:40
  • You have to leave random mating. First, releasing random mating will change genotype frequencies SO it is evolution. eg : aa = blue Aa=green AA=brown, if not random mating, this biological feature will change its frequency, so population evolved. Moreover, you think human/mammals but many species also reproduce using clonality (so no "mating") which change again the evolution of both genotype and allele frequency. By the way, "random mating" includes 2 factors of evolution: reproduction modes (clonal vs sexual) and mating mode (selfing, inbreeding, panmixia, outcrossing). – sol Sep 12 '17 at 09:10
  • Please, delete your edit and reintegrate "random mating" as it is the major factor to explain evolution (eg http://ebd10.ebd.csic.es/pdfs/Duminil_etal_2007_AmerNat.pdf ; Charlesworth (2003, p. 1052): “The mating system is probably among the factors with major effects on variability, clear enough to be discernible even in the presence of other factors.” – sol Sep 12 '17 at 09:10
  • I downvoted for the removal of random mating. As sol noted, it is critical to the understanding of evolutionary change in a population. – Bugmo Apr 10 '18 at 01:52
  • @Bugmo I already had "no sexual selection" in the answer so the whole random mating issue is covered. Nonetheless, it does appear to have caused confusion so, I agree it is best removed. – DQdlM Apr 10 '18 at 17:30
  • In the real world this boils down to does it have heritable characteristics and does it reproduce? If yes to both it will evolve. good answer though – John Apr 11 '18 at 03:50
  • @KennyPeanuts You might want to add something like If one were to use another definition of evolution (see [How to define “evolution”?](https://biology.stackexchange.com/questions/11400/how-to-define-evolution) for a discussion), of course the below list of mechanisms that are driving evolution would be different. to deal with users that are bothered by the quite standard definition you're using. +1 – Remi.b Apr 14 '18 at 14:26
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What is evolution?

The first step is to remind ourself of the definition of the term "evolution". Evolution is most often defined as "any change in allele frequency in a population". I will assume that you are willing to use this standard definition.

If one were to use another definition of evolution (see How to define “evolution”? for a discussion), of course the below list of mechanisms that are driving evolution would be different.

Forces that drive evolution

Categorizing the processes that affect allele frequencies might be subject to issues of semantics. Without going into the details, we generally recognize 4 forces that drives evolution

  1. Natural selection
    • Natural selection refers to the deterministic change in allele frequency due to a differential in fitness among different genotypes. Sexual selection and artificial selection are typically considered as part of natural selection (although that may vary from author to author)
  2. Genetic Drift
    • Genetic Drift refers to the stochastic sampling process of individuals
  3. Mutations
    • A mutation refers to any spontaneous change (substitution, indel, chromosome duplication, etc...) in an individual's genotype.
  4. Gene flow (aka. migration)
    • Gene flow refers to the transfer (migration) of DNA sequences among populations.

KennyPeanuts's answer, random mating and hardy-weinberg equilibrium

In his answer, @KennyPeanuts also talk about random mating. Random mating refers to the condition where the probability of two individuals to mate depends only on their respective fitness. Many people phrase random mating as absence of mate choice but it actually refers to the absence of variation for mate choice in the population.

Hardy-Weinberg states that under the above four conditions and random mating, then the frequency of the genotype that has the allele $i$ derived from the mother and the allele $j$ derived from the father, where $x_i$ and $x_j$ are the frequency of these alleles is $\cdot x_i \cdot x_j$. This means that for a bi-allelic locus, the allele frequency of the genotypes AA, AB, BA and BB are $x^2$, $x(1-x)$, $x(1-x)$ and $(1-x)^2$, respectively where $x$ is the frequency of the allele A. For the heterozygotes (AB and BA), we often care little which of the two allele is inherited by the mother and which is inherited by the father (assuming there are genders) and we therefore call AB both AB and BA genotypes (which can eventually be confusing). As such, the frequency of the AB genotype is $2 x(1-x)$.

The condition of random mating ensure that there is no deviation of genotype frequencies from the Hardy-Weinberg's expectations and it ensure that there is no change in genotype frequencies from the first to the second generation considered (after one generation, the equilibrium genotype frequency is immediately reached). Random mating is therefore not a condition for evolution to not occur.

Remi.b
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  • Evolution: change in the frequency, not of "allele frequency" but of heritable biological feature, – sol Sep 12 '17 at 09:11
  • The usual so called "population genetics definition" of evolution refer to change in allele frequency. It is a very standard definition. You might want to put emphasis on the phenotypic trait that which variance is at least caused by genetic variance but the detail definition gets a little trickier. – Remi.b Apr 10 '18 at 17:33
  • "Science sans conscience n’est que ruine de l’âme" Rabelais (Pantagruel) and “The enemy is the gramophone mind, whether or not one agrees with the record that is being played at the moment.” Orwell (Essays)...So, you might have one locus, two alleles A & B, let's say f(A)=0.5, f(B)=0.5, if at generation t, you have all diploid (but works with polyploid also) individuals [AA] and [BB], the next generation t+1, all individuals are all [AB], you HAVE evolution while "allele frequencies" have not changed. You get it? In popgen, mass thinks in alleles but as Ewens 2004 tells, genotypes only matter – sol Apr 11 '18 at 10:10
  • ...and that's one of the multiple point you miss by saying "Evolution = change in ALLELE frequencies", so replace by "change in heritable trait (can be genotype, phenotype) frequencies". Pop gen comes from information sciences. This definition includes also heritable but non mendelian traits, which changes in frequencies are also evolution. – sol Apr 11 '18 at 10:14
  • I am repeating a very standard definition. I am well aware of its limitations. A definition is completely arbitrary and it may or may not fit the intuition. You are free to use the definition you want. In no way am I claiming that this definition is the only, pure and perfect definition. It is just a simple and very standard one and I think that when someone asks what causes X everyone would expect the person answering to use the standard definition of X. Your citations of Rabelais and Orwell are really off-topic btw. – Remi.b Apr 11 '18 at 16:35
  • Note that your definition is slightly unclear as many of the considered traits take continuous values and therefore, one cannot consider a frequency without making arbitrary grouping of those values. Also, your definition depends upon the concept of heritability and the heritability of trait themselves vary through time, among environments and among populations. Also, the (sometimes arbitrary) grouping of individuals into populations will affect heritability of traits. – Remi.b Apr 11 '18 at 16:47
  • Your definition will likely run into problems when considering things like reaction norm (and reaction norm of the slope of the reaction norm), developmental noise, niche construction too. So do not think you found the holly grail with your definition! – Remi.b Apr 11 '18 at 16:47
  • Don't be gripped in the vice of an excessively rigid definition which ultimately will make the concept open to challenge. Repeating a definition because it is "standard" is not scientific but dogmatic. Moreover, a parsimony approach tells us that there is no need for this term added: "allele" to this definition, if not to enclose the thought. Finally, where did you see that this definition is standard? I quote you a reference book in gen pop that says the opposite, what are your sources? Dear Black knighnt, read more books and original articles before throwing Holy Hand-Grenade of Antioch. – sol Apr 13 '18 at 07:05
  • Let's not extend this discussion too much. I have justified the use of this definition, not because it matches better the intuition than other definitions but for the fact that it is what people usually mean. I have also highlighted why your definition was in no way better. I don't think there is much interest to keep arguing on it, esp. if you start calling me "black knight" or naively accuse me of not reading many original articles in the field. – Remi.b Apr 13 '18 at 16:16
  • If you want to discuss the definition of evolution you should have a look at the post How to define “evolution”?. I will likely not answer to further comments of the kind here. – Remi.b Apr 13 '18 at 16:17