I am trying to find a case/study where scientists documented a mutation in an animal or human that was to the benefit of the host.

The closest thing I have been able to find is sickle cell anemia (SCA) helping to fight malaria. However, the life expectancy for people with SCA is 40 – 60 years, and in 1973 it was only 14 years (source). I am looking for another case, preferably one that is not life-threatening.

Are there any other cases where a beneficial mutation — one where the good outweighs the bad — was documented?

By beneficial I simply mean that it helps or protects the host in some way, while not causing substantial harm. As in my example of SCA it can benefit the host if the host lives in an area with malaria. However, it is also life threatening and reduces the life expectancy of the host.

If — for example — SCA would only cause pain and not be life-threatening, then it would (in my opinion) be a beneficial mutation. While not purely beneficial, it would still increase the life expectancy of people living in an area with a high occurrence of malaria.

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    $\begingroup$ Macroevolution means that 2 groups of organisms diverged far enough that they cannot interbreed any longer and thus now form separate species. en.wikipedia.org/wiki/Macroevolution I am not sure what you mean with "a purely beneficial mutation". A mutation/variation doesn't need to be "purely beneficial" (if something like that even exists). It just needs to be beneficial ENOUGH to prevail and spread in the population. $\endgroup$
    – a tiger
    Feb 27, 2017 at 12:21
  • $\begingroup$ A beneficial mutation would be a seal born with functional legs, allowing it to hunt on land. A non beneficial mutation being a seal born with an extra flipper, the extra flipper does not benefit the seal and would only slow it down. $\endgroup$
    – user30163
    Feb 27, 2017 at 12:37
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    $\begingroup$ A seal born with functional legs would be a detrimental mutations as legs would slow down a swimming speed.Making hunting in water more difficult and increases the likelihood of said seal pup being eaten by sharks it is first year of life. $\endgroup$
    – JayCkat
    Feb 27, 2017 at 13:49
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    $\begingroup$ Once you've managed to clarify your question for yourself, you might want to have a look at this skeptics.SE post which links to thousands of evidence for evolution that have been simplified for layman. $\endgroup$
    – Remi.b
    Feb 27, 2017 at 14:07
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    $\begingroup$ In the current form, I think the question is fine. There is some ambiguity in how to judge whether a mutation is "beneficial", but I think there are answers where this becomes obvious. One example might be the deletion in the CCR5 gene that renders people resistant to HIV, academic.oup.com/femsle/article-lookup/doi/10.1016/… I am voting to reopen. $\endgroup$
    – Roland
    Mar 1, 2017 at 7:51

4 Answers 4


The answer depends on what you mean by "observed".

Bacteria acquire antibiotic resistance genes all the time, for example. This happens 'in the wild', but you can see in the lab that bacteria can become resistant overnight - I'd call that 'observed'.

There are many papers about the emergence of antibiotic resistance (not that I'm suggesting this is the only observable beneficial mutation).

In this paper, for example, several spontaneous mutations are induced in H. pylori in the lab in a short space of time:


In this paper, estimation of mutation rates are attempted in the emergence of resistance: http://aac.asm.org/content/44/7/1771.full

It should be pointed out however that the timeframes can vary wildly. If a bacteria acquires a resistance gene by horizontal transfer, for example, this could be considered virtually instantaneous. Spontaneous mutations may take longer to emerge, and might only do so in the presence of steadily increased selection pressure, by contrast.

  • $\begingroup$ Without additional explanation or resources/citations, this is not a proper answer. This is a comment. Please see How to Write a Good Answer. Thanks. $\endgroup$ Feb 27, 2017 at 14:41
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    $\begingroup$ Well as a microbiologist it's based on personal experience. I believe that the acquisition of resistance genes by bacteria is such a widely accepted and cited example now that it didn't need an implicit source, much as I wouldn't cite Watson and Crick every time I mention DNA... $\endgroup$
    – Joe Healey
    Feb 27, 2017 at 14:43
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    $\begingroup$ By observed I mean some scientist dude was all like; yo this bacteria's gone all resistant, I should write this down. So you got that right. Would be nice to have an example of a specific type of bacteria with a link to the study or report where it happened. $\endgroup$
    – user30163
    Feb 27, 2017 at 14:46
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    $\begingroup$ Though you're right, that doesn't change the need to provide necessary citations/sources. Clearly the OP likely doesn't know as much about this subject as you or they wouldn't be asking the question. Without substantiating our answers with good sources, we'd be no different from Yahoo Answers or other error-ridden Q&A sites. By providing valid sources, we can better assure our visitors (as well as each other) that the information being shared is accurate. $\endgroup$ Feb 27, 2017 at 14:46
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    $\begingroup$ @JoeHealey of course. But on this site, those undocumented experiences belong as comments or as anecdotal additions to otherwise cited answers. (This is the whole conept behind peer-reviewed science!). Thanks for updating your answer with examples :). $\endgroup$ Feb 27, 2017 at 15:22

Lactase persistence

This is a somewhat unusual example but has been well studied, and would seem to satisfy the criteria of the question. Let me start by quoting the Wikipedia entry for those unfamiliar with the phenomenon:

Lactase persistence is the continued activity of the enzyme lactase in adulthood. Since lactase’s only function is the digestion of lactose in milk, in most mammal species, the activity of the enzyme is dramatically reduced after weaning.[1] In some human populations, though, lactase persistence has recently evolved[2] as an adaptation to the consumption of nonhuman milk and dairy products beyond infancy.

Studies on the geographical distribution of lactase persistence (e.g. AJHG (2014) vol 94, pp. 496–510) show that lactase persistence is associated with cultures which practice pastoralism (specifically herding bovines), supporting the hypothesis that the trait evolved because of the benefit it conveyed to such populations in allowing them to use bovine (or caprine or ovine) milk to survive in adulthood.

There is no doubt that lactase persistence is a heritable — i.e. genetic — trait, as can be seen from consulting the OMIH (Online Mendelian Inheritance in Man) entry. This has extensive documentation, including description of the base changes associated with the trait:

Enattah et al. (2002) found a complete association between biochemically verified lactase nonpersistence in Finnish families and a C/T(-13910) polymorphism of the MCM6 gene (601806.0001) roughly 14 kb upstream from the lactase gene locus (LCT; 603202), located on 2q21. It was the C allele that associated with hypolactasia.

The molecular mechanism of lactase nonpersistence (the putative original human condition) — affected by mutation at this position — is still not completely clear. Recent work suggests:

Epigenetically controlled regulatory elements accounted for the differences in lactase mRNA levels among individuals, intestinal cell types and species.

Finally, I refer to the evidence for the Wikipedia statement that “lactase persistence has recently evolved[2]”. This is a paper by Bersaglieri et al. in The American Journal of Human Genetics (Am. J. Hum. Genet. 74:1111–1120, 2004). I am not a population geneticist, so I shall reproduce the relevant section of their summary unedited:

In northern European–derived populations, two alleles that are tightly associated with lactase persistence (Enattah et al. 2002) uniquely mark a common (∼77%) haplotype that extends largely undisrupted for 11 Mb. We provide two new lines of genetic evidence that this long, common haplotype arose rapidly due to recent selection: (1) by use of the traditional FST measure and a novel test based on pexcess, we demonstrate large frequency differences among populations for the persistence-associated markers and for flanking markers throughout the haplotype, and (2) we show that the haplotype is unusually long, given its high frequency—a hallmark of recent selection. We estimate that strong selection occurred within the past 5,000–10,000 years, consistent with an advantage to lactase persistence in the setting of dairy farming; the signals of selection we observe are among the strongest yet seen for any gene in the genome.

  • $\begingroup$ I have decided to mark this as the answer because it best fits with the question in its current state. Although the benefit from lactase persistence is small, it is beneficial and does not harm the host. $\endgroup$
    – user30163
    Mar 7, 2017 at 9:48

An example of a beneficial mutation we have probably all been on the receiving end of is the mutations of influenza. The whole reason we have to redevelop flu shots every year is because the influenza virus mutates so rapidly. Influenza loves changing its antigens to hamper our vaccine development and immune response. Normally you are immune to a pathogen after a single infection as our immune system recognizes the antigens on this pathogen in the future and reacts rapidly if it re-encounters them. This doesn't work with influenza as it mutates its antigens to the point that we can no longer recognize them from a previous flu infection, forcing our immune system to start all over again. This is what makes the flu so problematic for us; for influenza it is rather beneficial to put it mildly.

There are also specific human examples, some of which are mentioned in other answers. A mutation in low-density lipoprotein receptor-related protein 5 has been associated with improved bone density. This improvement in bone strength has fairly obvious advantages, like harder to break bones and improved resistance to age related skeletal weakness. Asides from (seemingly harmless) bony growth in their mouths no negative side effect of this mutation was discovered.

A particularly crazy human one is the potential of tetrachromacy (seeing 4 colors) in women. I'm not entirely sure about the genetics and test methods involved but apparently in this study they discovered that one mother of a color-blind male displayed genuine tetrachromacy.

  1. Smith, D. J., Lapedes, A. S., de Jong, J. C., Bestebroer, T. M., Rimmelzwaan, G. F., Osterhaus, A. D., & Fouchier, R. A. (2004). Mapping the antigenic and genetic evolution of influenza virus. Science, 305(5682), 371-376.
  2. Boyden, L. M., Mao, J., Belsky, J., Mitzner, L., Farhi, A., Mitnick, M. A., ... & Lifton, R. P. (2002). High bone density due to a mutation in LDL-receptor–related protein 5. N Engl J Med, 2002(346), 1513-1521.
  3. Jordan, G., & Mollon, J. D. (1993). A study of women heterozygous for colour deficiencies. Vision Research, 33(11), 1495-1508.

Yes, many beneficial mutations have been documented, here are a few examples:

The Lenski experiment : https://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment
(the repeatable observation of the evolution of citrate metabolism in E.coli)

The Milano mutation : https://en.wikipedia.org/wiki/ApoA-1_Milano, http://blogs.sciencemag.org/pipeline/archives/2016/11/16/the-long-saga-of-apo-a1-milano
(a mutation in humans that gives resistance to heart disease; its first appearance wasn't observed per se but phylogenetic analysis allowed the identification of the first person with it, a guy called Giovanni Pomarelli in the 1700s)

The myostatin mutation in the German "super-baby" : http://www.nbcnews.com/id/5278028/ns/health-genetics/t/genetic-mutationturns-tot-superboy/#.WLkojjvyuUk

The nylonase mutations : https://en.wikipedia.org/wiki/Nylon-eating_bacteria

Antibiotic resistance in the bacteria Mycobacterium Smegmatis : https://www.sciencedaily.com/releases/2017/02/170221110808.htm
(this article looks at specific mutations) (FIRST EDIT: turns out that like the Lenski experiment it involves actually looking at the bacteria as they evolve the traits and looking at exactly what happens step-by-step. Awesome !!)

Another example gotten from a Google Scholar search for "beneficial mutations":

Quote from the abstract: "The naturally occurring human lipoprotein lipase S447X variant (LPLS447X) exemplifies a gain-of function mutation with significant benefits including decreased plasma triglycerides (TG), increased high-density lipoprotein (HDL) cholesterol, and reduced risk of coronary artery disease."
(note this isn't the same as the Milano mutation, see also this article about the discovery of this mutation and its development as a medical therapy :
http://online.liebertpub.com/doi/abs/10.1089/hum.2013.063 )

And another study of antibiotic resitance-related mutations, in the pathogen Pseudomonas aeruginosa:

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    $\begingroup$ Please do not only drop in links, write an answer that stands for itself and has the references for further reading. $\endgroup$
    – Chris
    Mar 3, 2017 at 8:31
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    $\begingroup$ @Chris the question was "Are there any cases where a beneficial mutation was documented" in the context of "I am trying to find a case/study where scientists documented a beneficial mutation in a human or animal", so I don't really see a better answer than "Yes there are, here are references to such studies/cases". I admittedly didn't have the "Yes" part, so I hope adding it was sufficient: $\endgroup$
    – Oosaka
    Mar 3, 2017 at 9:16

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