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Natural selection is the differential survival and reproduction of individuals due to differences in phenotype.

Natural selection, a process that results in the adaptation of an organism to its environment by means of selectively reproducing changes in its genotype or genetic constitution.

Natural selection, then, can be defined as the differential reproduction of alternative hereditary variants, determined by the fact that some variants increase the likelihood that the organisms having them will survive and reproduce more successfully than will organisms carrying alternative variants.

Darwin's definition of natural selection his book "On The Origin Of Species By Means Of Natural Selection or the Preservation Of Favoured Races In The Struggle For Life" is:

The preservation of favorable variations and the rejection of injurious variations

In Evolution 101, natural selection is not defined, but rather the concept "evolution by natural section" is characterized as the outcome of variation, differential reproduction and Heredity, and a clarifying example is provided.

Clearly, the wording in each of the above is different!

I searched Biology StackExchange for any explicit statement of the definition of natural selection, I couldn't manage to find one. There are some discussions about whether it is a tautology or not, but even in those discussions, the definition of natural selection was not quoted.

I tried to search tags "natural selection" and "definitions" of biology StackExchange, and yet I didn't see any particular wording mentioned as the official definition of natural selection.

Actually, the tag [natural selection] mentions this definition in the tag information itself:

Natural Selection is a mechanism of evolution that leads to non-random spread of genes due to the effect that genes have on reproductive success

Natural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations.

Is there an official definition of natural selection that is adopted by biologists nowadays? and what is that definition exactly?


[EDIT] It came to my awareness that this question might be a possible duplicate of the following question: "How is Selection best defined", and indeed in the answers provided to that question the topic of definition of natural selection has been addressed.

I didn't know of this posting. I simply surfed for "natural selection", and not just for "selection", and I didn't notice it. But indeed what's presented in the answers does cover the question present here.

However there is some difference in the question itself from that present here. Here I wanted to know of what I thought would be an official definition, and I was asking in particular about "natural selection", while in the referred question, the question is more general, it's about what qualifies "any" force (apparently he means related to biology and especially evolution) to be labeled as "selection", including artificial selection, sexual selection, etc.., so it's a wider topic, at least as far as terminology is concerned.

Here in this question I've quoted the main results that one would see upon surfing the web for "definition of natural selection", and I wanted to know which one would be the official or as @Remi.b had put it, the most commonly used or referred to in biological research.

I still think, that for precision purposes, exact wordings are important, and such an extremely important concept like "natural selection", it would have been expected that it had an agreeable, kind of, official definition, by some convention or the alike.

Anyhow, I think, whether this question is a duplicate or not, can be better assessed by experts in evolution field present in this website, like those who provided answers, and others.

Thanks.

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    $\begingroup$ I think it's unrealistic to expect to find word-for-word congruence b/w definitions from multiple sources. All your definitions still describe the same phenomenon conceptually. From a broader viewpoint, no 2 textbooks (or at least few) define "simpler" biological concepts the same (e.g., even the word cell). The same can be said of common non-scientific words (e.g., see dictionary.com, OED, Merriam-Webster, etc. for any given word). In conclusion, there is no "official" wording for this definition or most definitions. This is why bio instruction emphasizes learning concepts not words... $\endgroup$ – theforestecologist Mar 13 at 19:04
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    $\begingroup$ Then there's the definition which pops up when you hover your cursor over the tag "natural-selection" at the bottom of this question. $\endgroup$ – mgkrebbs Mar 13 at 20:05
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    $\begingroup$ Of all the definitions, I think the SE tag one is possibly the worst. Maybe @Remi.b would take a stab at editing it, if you agree? $\endgroup$ – Bryan Krause Mar 13 at 20:34
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    $\begingroup$ @Remi.b I think Bryan Krause was suggesting you to edit the the natural-selection tag-info in SE. $\endgroup$ – user237650 Mar 14 at 5:29
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    $\begingroup$ Possible duplicate of How is "selection" best defined? $\endgroup$ – fileunderwater Mar 15 at 10:44
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Official definition

Is there an official definition of natural selection that is adopted by biologists nowadays? and what is that definition exactly?

I don't think there is such a concept as an "official definition" of any concept in science. There are common definitions though.

The definitions you cite

Let's go through your three definitions

Natural selection is the differential survival and reproduction of individuals due to differences in phenotype.

This definition lacks the idea that this fitness differential must be caused, in part at least, by genetic variation.

Natural selection, a process that results in the adaptation of an organism to its environment by means of selectively reproducing changes in its genotype or genetic constitution.

Part of the phrasing is about the consequence of the process rather than the process itself. The part that describes the process itself is "selectively reproducing changes in its genotype, or genetic constitution", which is a rather unusual phrasing and I would argue is slightly vague.

Note that while most authors refer to natural selection as the fitness differential, it is not impossible to refer to natural selection as the resulting change in allele frequency. I have never seen cases where this semantic difference matters though.

Natural selection, then, can be defined as the differential reproduction of alternative hereditary variants, determined by the fact that some variants increase the likelihood that the organisms having them will survive and reproduce more successfully than will organisms carrying alternative variants.

I have never encountered the expression "alternative hereditary variants". I think the author made it up. It sounds like the author tried to avoid the term "allele" by replacing it with "alternative hereditary variants". The author also seems to have tried to avoid the term "fitness" by replacing it with "likelihood that the organisms having them will survive and reproduce more successfully".

But overall the definition sounds correct to me. There is an important difference between the first and the third definition is that in the first definition, it emphasizes the fact that the genetic elements that explain fitness variance are doing so via its effect on the phenotype. The third definition just ignores phenotype. As such, I would consider the first definition more complete (and more compact).

Natural Selection is a mechanism of evolution that leads to non-random spread of genes due to the effect that genes have on reproductive success

Here, the definition is again very much based on the consequence of the process rather than the process itself. Only "due to the effect that genes have on reproductive success" refers to the actual process of natural selection.

I don't really like the term "random" here as the concept of randomness is somewhat unpleasant to define outside of a well-defined model. I don't really like the term "genes" either because selection doesn't only act on genes (but can act at any locus) and because the term "allele" would be more appropriate even if the phrasing would still remain unclear.

So in short, shame on us, the StackExchange definition is pretty bad!

The preservation of favourable variations and the rejection of injurious variations

I shall not talk here about how different is Darwin's theory of evolution from today's theory of evolution (which is called the "modern evolutionary synthesis"). I shall not talk either whether this single short sentence is a good summary of Darwin's representation of natural selection (see @Luaan comments for more information).

This definition is short and a bit vague. One would want to think of this definition as applying to a genetic variant, without regard to the phenotype, however, Darwin did not know anything about DNA.

My favourite definitions

Lewontin's recipe

A very simple way to think of natural selection is to consider Lewontin recipe. The Lewontin recipe says that natural selection occurs whenever:

  1. Individuals in a population vary in terms of a given trait

  2. This trait has a non-zero (additive) heritability. See this post for a definition of heritability.

  3. The fitness varies (not necessarily linearly) as the trait varies

Single sentence definitions

If you prefer a shorter and simpler version I would personally suggest

Selection is the fitness differential among genotypes in the population.

This definition lacks the concept of phenotype but talking about the fact that an individual fitness is dependent on its phenotype (among other things) is, IMO, not required to mention in the definition of what natural selection is. Not that I also removed the term "natural". I don't quite like it because it leads people to think that natural and artificial selection could be fundamentally different. Same applies to sexual selection, IMO, but I shall not go down this slope now!

In a very similar post, I wrote the definition

Selection is a fitness differential associated to a genetic variance among individuals in a population.

I also like this definition because it highlights that selection acts on populations (and not on individuals or on species).

Mathematical modelling

You might want also to consider as a definition the mathematical modelling of the process. In absence of genetic drift (assuming infinite population size), assuming a bi-allelic locus with alleles a and A, one can model (haploid) selection as

$$p_{t+1} = \frac{p_t W_a}{p_t W_a + (1-p_t) W_A}$$

, where $p_t$ is the frequency of the allele a at time $t$. $W_a$ and $W_A$ are the fitness of the genotype with alleles a and A, respectively. Of course, you can extend this model to any kind of ploidy and any number of alleles. You can also extend this model to include genetic drift (typically done via the use of diffusion equations or via branching patterns).

For more information about these mathematical modelling, please have a look at an intro book in evolutionary genetics (see here for book recommendation).

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  • $\begingroup$ @This is a very nice answer. I noticed that you skipped Darwins' definition? $\endgroup$ – Zuhair Al-Johar Mar 14 at 10:46
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    $\begingroup$ @ZuhairAl-Johar Keep in mind that Darwin was simply defining his terminology for the book. This is similar to saying "James McKay (hereafter noted Defendant)...". The idea worked, the concept stuck, and the exact wording and semantics of the "definition" aren't important in the slightest - in general, in scientific thinking, the concept is far more important than the exact words you use to describe it. Scientists usually aren't language lawyers, they're just trying to communicate efficiently :) $\endgroup$ – Luaan Mar 14 at 13:19
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    $\begingroup$ @ZuhairAl-Johar It should further be noted that your cited part is the end of a whole paragraph where he describes what he means by natural selection (see counterbalance.org/evolution/direct-frame.html). And some of the definitions you showed focus on some mechanisms that we've found since Darwin's time - mainly, genetics (and the language of genetics). Darwin was talking about "individuals having any advantage ... would have the best chance of surviving", but that's equivalent to "some phenotypes promote survival" - just with more mature terminology and more insight. $\endgroup$ – Luaan Mar 14 at 13:24
  • $\begingroup$ @ZuhairAl-Johar You should consider reading the edit, which add discussion of the Lewontin recipe and add my own definition. Also, I quickly discussed "Darwin's definition" as you asked. $\endgroup$ – Remi.b Mar 15 at 3:53
  • $\begingroup$ @Remi.b, why the first p in the equation is not in upper case? $\endgroup$ – Zuhair Al-Johar Mar 25 at 4:52
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I've adapted your definitions to another process that I think will be less controversial to you.

Eating is the intake of food by taking into the mouth, chewing, and swallowing.

Eating, the process that results in digestion by taking in food and chewing and then swallowing.

Eating, then, can be defined as the intake and digestion of food items, determined by the fact that organisms take in foods to the mouth and then chew and swallow them leading to digestion of those foods into nutrients used by that organism.

If you look up dictionary definitions of the verb "to eat" you will also get a variety of answers, but there is no controversy about what "eating" is: it's a concept you learn and agree on. Some of the definitions reach further, mentioning digestion. Some focus on the "just eating" part. However, they all agree with each other, there is no conflict. In fact, a lot of the words are just rearrangements of the same words into different grammatical constructs.

All of the definitions you cite are reasonable descriptions of the term; all of the sources you cite also go further into those definitions to describe the whole process. You should focus on that whole process rather than trying to find fault in the definition. Natural selection is not a tautology, and arguments that it is are misguided.

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  • $\begingroup$ You've cited the same citation that I've cited. I'm not arguing that it is a tautology, I just wanted to know the definition, and all of your responses were great. Thanks $\endgroup$ – Zuhair Al-Johar Mar 13 at 20:28
  • $\begingroup$ There is some variation as to whether it's thought of as acting on the phenotype or the genotype, although of course those two are interrelated. $\endgroup$ – Acccumulation Mar 15 at 15:32
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As Remi points out there is not an official definition of anything as complex as natural selection in science. Science is a collective consensus, not a hierarchical structure, official things are rare and usually not directly connected to the science. The neo-Darwinian synthesis might count but that is far too large to be considered a definition, it is more a modern restatement of the theory.

I can offer the definition I use in class.

Selection: change in the heritable characteristics of a population due to differential reproduction of variations in said characteristics within a given environment

to break it down change in the heritable characteristics of a population... that's just a restatement of evolution essential for any consideration of natural selection.

...due to differential reproduction... so evolution happens because some things reproduce more successfully than other things.

...of variations in said characteristics within a given environment and this clarifies the cause of the differential, that variation in heritable characteristics exist and interact with the environment in different ways. Of course, it is important to understand the "environment" in this case is literally everything else, from other cells in the body to predators, to other genes on the same genome to abiotic processes.

Note authors tend to avoid the mention of genetics or related terms in the most fundamental definitions because natural selection is not reliant on nucleic acids it works with any form of heredity, an alien lifeform that has a different form of heredity will still undergo natural selection. Things like prions can also evolve via natural selection if a group of things has heritable characteristics that also vary in reproductive success natural selection will operate on those things.

Then you have the specification of "natural" selection. Which is simply selection not caused by human intervention. This has been an important piece of natural selection since the beginning mostly because people had little problem with the idea that humans could alter organisms by conscious choice but the idea that their natural environment could alter them simply due to survival and reproduction was not as easily accepted.

Differentiating natural selection and artificial selection is probably the vaguest part and has a tremendous amount of gray area. There is no Real difference between artificial and natural selection, it is all just down to human conceptual framing. Natural selection is just a response to an environment, but what makes up that environment covers everything from rocks, humans, members of the opposite sex, etc. Nearly anything can have an impact on survival depending on the circumstances. Because of this the only thing that differentiates natural from artificial selection is whether humans are the major environmental factor but that itself is vague, human mate choice and species that live around humans but are not domesticated( like cockroaches) make this imprecise. I have never found a satisfactory precise differentiation between the two forms of selection.

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natural selection was an idea proposed by darwin a scientist. he said that nature select the fittest. he concluded following points after his research In a population, some individuals will have inherited traits that help them survive and reproduce (given the conditions of the environment, such as the predators and food sources present). The individuals with the helpful traits will leave more offspring in the next generation than their peers, since the traits make them more effective at surviving and reproducing. Because the helpful traits are heritable, and because organisms with these traits leave more offspring, the traits will tend to become more common (present in a larger fraction of the population) in the next generation. Over generations, the population will become adapted to its environment (as individuals with traits helpful in that environment have consistently greater reproductive success than their peers).

Quoted from the book Darwin and Henslow The growth of an idea Edited by Nora Barlow

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  • $\begingroup$ Thanks for this nice quote. But is this predictive? I mean suppose that it has always been a merry time for trait A and bad for trait B, then according to what you've said one would predict that trait A would prevail since it has more capacity to adapt to its environment and thereby survive and reproduce more. Now suppose suddenly an outbreak of a deadly disease spread that trait A happened to be susceptible to but not trait B, the outcome is final triumph of trait B, and the extinction of trait A. $\endgroup$ – Zuhair Al-Johar Mar 23 at 15:55
  • $\begingroup$ What was usually the weaker trait, i.e. the less fit trait, prevailed in this example. Now a selection had been made, but for what? for what used to be the less fit trait? Its done by nature. So it doesn't appear that nature always select in favor of the most fit traits? isn't it. $\endgroup$ – Zuhair Al-Johar Mar 23 at 15:55

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