Evolutionary Experiments Show Natural Selection Opposes Sexual Selection

Assassin Bug and Broad-Horned Flour Beetle

An assassin bug approaching a male broad-horned flour beetle. Credit: University of Exeter

Natural selection can reverse evolution that occurs through sexual selection and this can lead to better females, new research shows.

The study — led by the University of Exeter and Okayama University — examined broad-horned flour beetles, whose males have exaggerated mandibles, while females do not.

Male beetles with the largest mandibles win more fights and mate with more females — an example of “sexual selection,” where certain characteristics (like a male peacock’s tail) improve mating success.

However, having bigger mandibles requires a masculinized body (large head and neck), and a smaller abdomen — which, for females, limits the number of eggs they can carry. A masculinized body is not good for females.

Experimentally enhanced natural selection through predation, however, targets the same males favored by sexual selection and this results in the evolution of less masculinized bodies and better-quality females.

Broad-Horned Flour Beetles

Broad-horned flour beetles. Credit: University of Exeter

In the study, broad-horned flour beetles were exposed to a predator called the assassin bug, which ate males with the largest mandibles.

By removing these males, predation effectively reduced the benefits of sexual selection and this means natural selection has an increased impact.

After eight generations of this, females produced about 20% more offspring across their lifespan, compared to a control group of beetles where large-horned males were not removed by predation.

“Males and females of every species share genes, but in some cases — including broad-horned flour beetles — the genes good for one sex aren’t always ideal for the other,” said Professor David Hosken, of the University of Exeter.

“We see this process, known as intralocus sexual conflict, across the natural world.

“For example, humans share the genes for hips — which males need for walking, and females need for both walking and childbirth. Optimal hips for women would be broad enough to allow childbirth, while optimal hip width for men is narrower.

“Humans reach a sort of evolutionary compromise, in which neither males nor females get the body shape that would be optimal for them.”

Professor Hosken added: “Our findings show that sexual selection favoring large-horned males drags female body shape away from the female optima.

“This study helps us understand two evolutionary tug of wars, one between natural and sexual selection and the other that takes place over body shape and characteristics shared between the sexes.”

Reference: “Natural selection increases female fitness by reversing the exaggeration of a male sexually selected trait” by Kensuke Okada, Masako Katsuki, Manmohan D. Sharma, Katsuya Kiyose, Tomokazu Seko, Yasukazu Okada, Alastair J. Wilson and David J. Hosken, 8 June 2021, Nature Communications.
DOI: 10.1038/s41467-021-23804-7

Funding for the study came from the Leverhulme Trust and the Japan Society for the Promotion of Science.

59 Comments on "Evolutionary Experiments Show Natural Selection Opposes Sexual Selection"

  1. Anyone who beleives this BS is of natural selection…lmbo

    • Torbjörn Larsson | June 10, 2021 at 12:51 pm | Reply

      Evereyone who is interested in the basic process of biology accept the fact [ https://en.wikipedia.org/wiki/Evolution ].

      “Belief” is for the know-nothing superstition followers, obviously. But why do they comment on science, if they don’t feel threatened in their self imposed ignorance?

      • Please Explain what part of them using “Assassin bugs to kill the larger males” is Natural Selection. You have 2 options red ball, blue ball. I pop the blue ball. What choice do you have? None you are left with a red ball. And then I say it was natural that you choose the red ball. This is literally what they did.

        • Tesseractjane | June 12, 2021 at 5:40 pm | Reply

          I think the article clearly defines the premis of the experiment as “laboratory controlled enhanced natural selection.”

          Weird flex.

          • Yes, it does. But the average trader after finishing the article has forgotten those very specific statements. That’s a, “cover my a**” statement but we need people to read this so to cover legal symmetries, it must be included. Again, peer reviews… Where are they?

      • Why did they have to force in an invasive species to find this conclusion, you might ask; the answer: to build a narrative and an influence on future human thought/thinking. You can call it whatever catchphrase you want, this is today’s version of society attempting to eliminate masculinity and blurr the lines of 2 genders. It’s all connected, every conversation that is geared towards a specific narrative. And for those that are in any field that ANY test is studied, I’m not saying you’re a representative of said narrative, but referencing back to modern pop culture and society, it always heads to the same game. You’re just pawns in it. Sorry to be blunt but there’s a societally hidden agenda with these studies. Whether it’s about bugs, trans gender people, racism, you name it; their tagline is we need to rethink everything we ever knew about anything, because Western society is incorrect. I know I went after a lot of topics on this post but they all bleed together to create an influence, regardless of what you read or listen to. How many peer reviews has this study had? That’s usually a thing when studies are done and they weren’t posted in this article… Just saying.

    • Agreed! Someone just made the comment about the article clearly stating it was a laboratory controlled experiment but they mention that once and scream natural selection throughout. It’s to plant a seed in the minds of the absent minded reader; which they know is the average trader. “It’s written so it must be true, scientists studied it… Blah blah blah”

  2. Hahahaha the nerds are in charge all of a sudden and then they begin studies trying to prove why jocks actually shouldn’t be in charge. Trust the science!

    • Torbjörn Larsson | June 10, 2021 at 12:56 pm | Reply

      Why are scientists “nerds” and why wouldn’t you trust the facts and the process (science)?

      This is but an anecdote to keep it short, but scientists at large are into exercise and adventure:

      “Harrison Hagan “Jack” Schmitt (born July 3, 1935) is an American geologist, retired NASA astronaut, university professor, former U.S. senator from New Mexico, and the most recent person still living to have walked on the Moon.”

      [ https://en.wikipedia.org/wiki/Harrison_Schmitt ]

  3. Personally I find natural selection useless. It failed to give us human males gonads that don’t dangle dangerously on the outside–& we can’t blame that on mating season (wherein other mammals’ are said to only drop down then & retract later), since humans are always mating! Also my physician tells me the human foot could be better engineered.

  4. Valerie Schwandt | June 11, 2021 at 4:43 am | Reply

    They are making many assumptions as to what is best for the bugs, and for humans.

    • Tesseractjane | June 12, 2021 at 5:44 pm | Reply

      Premise one. Life propagates. The genes that spread the furthest win.

      Premise two, sexual selection can sometimes hinder the success of genes.

      Outside of these two premesis the scientists didn’t assume anything about the best interest of the test subjects.

  5. Wait why did they use other bugs to kill the males with the largest horns? They could have just removed them by hand on their own. It sounds like a complicated death trap from James Bond, just grab the ones with the big horns, don’t hire assassin bugs to kill them. You don’t even need to kill them in fact.

    • Tesseractjane | June 12, 2021 at 5:49 pm | Reply

      They weren’t testing the sexual selection process. They didn’t need to know the female bugs wanted horny males.

      They needed to remove the bug horn male genes. Because even though females don’t typically develop big horns the ones that had big horn daddies have bigger horns and are less able to carry eggs. By removing the big horn genes the females that were produced by smaller horned males had even smaller horns and more room to have more small horned babies.

    • LOL the irony!

  6. Yet, humans have found ways to deal with pregnancies for small hips or some other complications. It’s called a C-section. Let’s continue to believe that natural selection is constantly at play. There are many instances where natural selection was defeated. Also introducing an element not naturally present kind of removes the natural from natural selection doesn’t it? Finally, If increased reproduction is “better” then I guess India and China have the right idea? Stupid article.

    • Raymond Mroz | June 11, 2021 at 1:55 pm | Reply

      “Yet, humans have found…that natural selection is constantly at play.”

      And just what is your point, aside from setting up an obvious straw man fallacy.

      “There are many instances where natural selection was defeated.”

      Oh right, by the Edmonton Oilers in 7 games right?!? Seriously, what does this even mean?!?

      “Also introducing an element not naturally present kind of removes the natural from natural selection doesn’t it?”

      This statement clearly illustrates that you have absolutely no understanding of natural selection and that your are intellectually incapable of even placing these ideas into their proper context. This (peer-reviewed) research deals with biological forces which operate on a grand scale. Your repeated attempts to attack them at a granular level and with non-falsifiable pseudoscience and anecdotal evidence is, fallacious reasoning notwithstanding, utterly ridiculous.

      “Finally, If increased reproduction is “better” then I guess India and China have the right idea?”

      And finally, this little gem of your brings everything into focus. Aside from being patently false, it establishes one of two things as incontrovertible truth; that you are either a liar or an imbecile. At NO POINT in this article does it make *any* sort of claim that increased reproduction is “better”. In fact reproduction levels are NOT ADDRESSED ANYWHERE in this article nor are they even pertinent to the science being discussed. This is about natural selection, sexual selection as well as other factors and their impact on the development of the body types of a number of species along a spectrum running between the male/female optimum.

      All of which begs the question, did you even bother to read the article??? You and your fellow ‘true believers’ are certainly free to mindlessly devote your lives to the various and sundry magical beings whom you all so passionately follow. But how about doing the rest of us who are living in the 21st century a favour and keep your uneducated, irrational opinions to yourselves. Posting your non-falsifiable, pseudoscientific garbage on sites such as this will do very little to assuage the nagging ‘crisis of faith’ which is surely created by the massive and continually expanding corpus of scientific knowledge in our present age. Your gods truly have been pushed into the gaps. The teleological is all that now remains for you and your sort.

  7. Definitely far from natural. The females wanted the stronger mates but had to choose the weaker ones that were forced upon them. But it’s science 👀

    • Raymond Mroz | June 11, 2021 at 2:32 pm | Reply

      “The females wanted the stronger mates but had to choose the weaker ones that were forced upon them.”

      This idea is NOT present ANYWHERE in the previous article. So you are either just making it so that you can pin your straw man fallacy on it or you just have not read the article and have no understanding of the science found in therein. Sadly it’s probably a bit of both. I have never yet come across one of you superstitious twits who actually has any understanding of evolution by way of natural selection. You all pass links back and forth to sites authored by fellow kooks which contain irrational, fallacious pseudoscience coupled with blatant misrepresentation of the science which undermines your own non-falsifiable beliefs in magic and the supernatural. This process only serves to further strengthen the cycle of nonsense embraced by your group increasing the insular sub-culture by fostering an ‘us vs them’ mentality. The real tragedy is having to watch these people denying access to and undermining the development of logic and reason in their young when they choose to either home school them or send them to “schools” which fill their heads with lunacy and which discredit the application of logic and reason in problem solving. It’s a despicable, insidious type of abuse and I truly feel so sorry for those children who are robbed of an opportunity for sound intellectual development in their young lives. If you are a child of this type of abusive parenting then I am truly sorry. In fact, if that was the case in your upbringing maybe I have been a little too harsh with the ad hominems.

  8. “Experimentally enhanced natural selection”
    So actually, the selection wasn’t natural at all.

  9. This study ignores the fact that males are bigger and stronger for defense against predators. It also ignores the females desire for the stronger male. If the Beatles actually desired the weaker males the weaker males would have NATURALLY become the dominant gene over time. Attributing human emotions and rational to insect psychology is asnine. Just like shrodingers cat, either “COULD” be true, just like it “COULD” BE UTTER BS. THE SIMPLE FACT THAT I HAVE NEVER SEEN AN INSECT SHOW REMORSE FOR KILLING ANYTHING. I actually feel dumber having listened to this woke anti science scientists.

    • Well obviously they weren’t strong enough to resist predators, since they were eaten. They were testing whether sexual selection would be balanced by natural selection in a specific animal, nothing more nothing less. By natural selection, I mean via predation. There isn’t supposed to be a take away to humans or other animals

  10. Leave it to Japan. I don’t dislike Japan, but they are highly conservative and often fairly sexist, not that the US is much better. For context, beetles are are seen as masculine in Japan (I don’t know why) and child bearing hips is very much a concept. To compare beetles with a very specific stimulus (assassin bugs) to human mating is absurd. They created the environment that favored more petite beetles. They basically said “Women should be more feminine and men who aren’t strong have the advantage in reproduction.” Somewhere amongst those two “optimal” is where we’ll find these researchers preferences. Fun fact, women don’t lay egg batches. The natural enemies, environment, and demographics will decide the genetic preferences, not this.

  11. Carmi Turchick | June 11, 2021 at 6:57 pm | Reply

    Nope. Intersexual competition is NOT the same thing as sexual selection. Sexual selection would be the preference of female beetles for males with larger mandibles, instead we simply have males physically driving other makes away, and this is included in Darwin’s “competition for fitness limiting resources or mating opportunities” definition of natural selection. All this research has shown is that when we change the environment a species exists in, by introducing a new predator, it can result in changes in the physical features favored by evolution in a species, exactly as predicted by Darwin.

  12. Experimentally enhanced natural selection where an invasive species was suddenly introduced? So it wasn’t natural selection then?

  13. First of all ….what in the hell? Secondly,this was an absolute waste of my few minutes I took to read such a crap article.Anyone else feel body shamed?

  14. Your mom is ashamed. So is your cucked dad!

  15. So sorry your boyfriend left you for a more manly woman!…NOT!

  16. FAG!

  17. What is natural about this study?
    In nature, you know where natural actually exists, evolution has decided the way these bugs are is what is best for their species. This article sounds like more feminist BS science, where males of all species are bad for the females.

  18. Anonymous commenter | June 12, 2021 at 6:16 am | Reply

    A lot of people in these comments seem to be implying (or maybe projecting) a political agenda to this confused article. Really, I suspect the author may be confused about the difference between sexual selection and natural selection. Beetles aren’t sexually selective. The females don’t ‘select’, they let the males take care of deciding who mates. Thus the mandibles developed for male competition falls under natural selection. Thus is quite unlike sexual selection, such as in peacocks and other birds, where the females will refuse to mate with a male unless they pass the sexual selection criteria.
    They only meaningful part of this seems to instead looks at the shared inheritance of sexual traits and the genetic tug of war to produce a sexually dimorphic species.
    The headline for this article about natural selection opposing sexual selection is nonsense since nothing about sexual selection is even analyzed.

  19. Gary Hopkins | June 12, 2021 at 6:57 am | Reply

    If we use enough intelligence we can manipulate nature to “prove” just about anything.

  20. Erin Kitsune | June 12, 2021 at 7:15 am | Reply

    Murderers..

  21. Yet another PC study to “prove” how “toxic” masculinity endangers a whole freaking species, and how (bettle) life would be paradise if males were just a bit more like females.

    Thanks, I’ve had a good laugh.

  22. Evertime they figure something out, something comes along that destroys the latest evidence. I wish human beings would stop being so human all the time.

  23. I just realized that the focus of sex differences of the adults ignores an important part if this process: the survival rate of each egg. There likely is an optimal egg and batch size as different creatures run the spectrum of millions to one with those investing in one egg further investing into protecting that egg. The protector responsibility falling to one of the sexes, shared between both or shared by a herd.

  24. This is literally artificial selection and proves nothing we didn’t already know

    We get it, you hate men

  25. Its kind of hilarious how most critical thinkers in this thread can dispute the article with logical reasoning, and the so-called “science intellectuals” resort to personal attacks and inferences to pseudo science beliefs.
    This article, and the experiment was bunk.

  26. Heard all this before,excet that it was about female elepants figuring out poachers want ivory & choosing to mate with bulls who had smaller tusks.

  27. A lot of weirdos in the comments hand waiving the experiments away “ red ball blue ball” worst example you can think of while ignoring the obvious benefit of 20% offspring increase compared to the experiment when they had bigger mandibles, there were obvious benefits to the female but you people are so insecure you’re all some pseudo-scientist now that knows better, here to put the lab coat on as if you know what you’re talking about.

  28. I do not believe that you understand the insect politics.

  29. This sounds like a convoluted study to covertly support with “science” certain narratives of human social issues…

  30. Fascinating.

  31. You are not a scientist and if you seriously have a degree, you need to go back to the college and demand your money back. This is absolutely garbage and I feel bad for anyone who has had to read through it, you have stolen precious minutes of their life away that they could have spent actually learning something.

  32. Whoever wrote this article obviously failed science.

  33. The only I believe to hold true and validation is the case of rape. Rape is a process of elimination or frustrated rejection of elimination, so isn’t abuse. Why has it always existed in culture? Makes you think.

  34. Two things, first, humans aren’t insects (cept for opinions) and second, this is basically trying to tell women with already poor body images who are mentally susceptible because they have poor body images, that they can have a better body if they reject men, which even if that were the case it would take hundreds if not thousands of years for such changes to take place, it’s simply more hate, look at what men, women, and all races of humans have achieved, why are people risking it all to undo that, at a time where uncertainty is a certain? Wouldn’t it be better to have each thier own this increasing the overall odds of at least part of the species making it through? These are the proper questions, foget putting all the passengers in one lifeboat, it is surely going to sink!

  35. This delicate intricate balance is surely accidental. The idea of a creator, engineering, designing, overseeing and maintaining it is pretty farfetched. Baaaaaah!

    Romans 1:20
    For since the creation of the world God’s invisible qualities–his eternal power and divine nature–have been clearly seen, being understood from what has been made, so that people are without excuse.

  36. Interesting article with a bit misleading name. I guess “sexual selection” is more relevant to human beings..
    I do see humans as part of the nature, thus everything we do is natural in my opinion. My reflection on this article is this:
    It seems that mother nature thought of all of it thoroughly – If there is no danger female will benefit from a stronger more masculine male, while if there is a threat, the female will benefit from increased reproduction in order to survive genetically. Brilliant

  37. Shocker. Well healed scientists with a political axe to grind. This type of tripe now constitutes most of modern “science”, owing to funding sources which are often in direct conflict of interest towards an unwitting public (for all of you lightweights out there, that is a euphemism for stupid). A NON-study designed to have people come to the conclusion that females would be so much better off if only you eliminated those darn ‘big horned’ males. Hmm obviously we know do much better than mother nature. Seems size DOES matter. Ok, hurl your best insults at me. I’m an intellectual weakling who never studied or taught genetics and evolution… Oh that’s right, come to think of it, I remember teaching in my former life.

    • Sorry about the typos. I realize they distract but stupid phones are not the most user friendly for spelling comments correctly.

  38. Ruud Schmitz | June 15, 2021 at 2:11 am | Reply

    This article does not say: if jocks create offspring the women become off lesser quality then when nerds do. If that is what you read…. You are seriously insecure.

  39. The problem with this article is it is poorly explained and makes implications about humans it should not, and which I am sure the actual scientific article of the experiment did not make.
    The problem with nay-sayers in the comments is they dont know what words like “natural selection” actually mean.

    Natural selection confuses ppl only because it is a poor choice of title for the mechanism of evolution. In this word, natural does NOT neccessary mean “without man” and selection does NOT mean “active choice”. Stop taking the words literally. In science words mean differentthings than in life. (For examole, in regular life the word theory means a guess, in science a guess is called a hypothesis, and a theory is an explanation that all evidence points to).

    We could call it Mechanism X, it doesnt matter what we call it. It simply means “what survives and reproduces in the given environment”. If we leave a couple rats on an island it doesnt matter they came from people. In a few hundred yrs they could change the evolution of several species by predating.
    People introduce false predation to control evolution since animal husbandry took place about 10,000 yrs ago. Our culling dogs to shape the next gen of a breed is a mimic of predation.
    People in the comments act like this experiment says something about sex or gender. Thats not what its saying. Evolution is only about surviving long enough to reproduce and having as many babies as possible. So for us humans, who are conscious individuals, what is “optimum” for the species from an evolutionary perspective (for either sex) is NOT what is optimum for YOU, the individual man or woman.

    All the experiment suggests is that IF one sex of a species has a feature that makes them more competituve breeding, whether antlers to combat peets or bright feathers attract the opposite sex (ie sexual selection), but it drags them down so that predators get them (ie “natural selection”), in that case, survival (natural selectiin) will outweigh looking pretty (sexual selection). We already see that in nature so I dunno why they act like this is news.

    The experiment also observes that when that happened females could have more babies. In wild species, that is “optimum” from an evolutionary point of view, and quite frankly for the whole species. The father/male is also passing on more genes if his mayes are having more babies. So there is not a conflict between the “optimum” for males vs females, unless you are defining “optimum” differently for each, which would be a logical fallacy. Optimum means babies w your genes.The large mandibles are not optimal for males *in and of themselves*. The only reason the large mandibles were “optimum” for males, was bcus it was getting them females to have their babies. If its now getting them killed young, its no longer optimum. The optimum is to have medium size so you can still outperform other males but be small enough to not attract predator.
    The human example they give is just inappropriate.
    Usually out in nature, where one sex needs an extreme feature to breed more (like wider hips) that makes it harder to survive/run, and the other sex doesnt, the morphology of both winds up in the middle with the one who needs it being slightly exaggerated (such as the Q angle in womens hips, which is wide enough to increase risk of knee injuries).
    Its misleading to say men *need* narrower hips than they have, because we don’t. We all NEED not to have extremely wide hips,in order to walk and run, but at the same time women NEED very wider hips than they have, to get rid of the risk of childbed death (before tech as many as 25% died in childbirth). You dont even have to see men as involved in this pressure at all. Women with 3 ft wide hips wouldn’t be able to walk (humans were nomads for hundreds of thousands of yrs, so walking is required)but itd reduce the childbed risk. Women with narrow hips would perform well in outrunning predators but would die in childbirth. The compromise was made between womens survival and…womens survival. And womens survival is “optimum” for both women AND men passing on genes. eyeroll .

  40. PS Excuse the typos in my long comment. I have clumsy hands and a tiny phone and I dont see an edit button.

    PPS. I think some people are confused about what science and experimentation is. You cant just say experiments have no implications because they take place under controlled conditions. People act like field research is the only thing that matters, when lab research on evolution and natural selection is responsible and for many of things we take for granted and that keep us alive, particularly in medicine.

    You dont have to be as nerd to understand 10th grade biology.

  41. The article: “Being dead is generally a bigger obstacle to reproductive success than being unattractive.”

    The comments: “WoKe FeMiNiSt PrOpAgAnDa!!!!!!”

    To those of you saying the article made you dumber, I really don’t think you needed the help.

  42. Interesting but it’s well known that sexual selection is often dysgenic. Just look at a peacock male… Didn’t really need an experiment did it?

    Take a moment to think about how this basic fact impacts modern society where sexual selection of males is turned up high and natural selection is mostly eliminated.

  43. Christopher McIlroy | June 15, 2021 at 1:38 pm | Reply

    Without the large horns they will simply die to predators. Right? That is a defense mechanism developed over time to survive. What does it matter of the female can carry 20% more eggs if they just die immediately because they lost their defense mechanism.

  44. The comments made by philistines and the retorts by the educated, is almost more interesting than the article itself.
    For one it proves the bell curve (normal distribution, not the book) of human intelligence and how it’s mean should shift left. Unfortunately this is a phenotype that isn’t as attractive as having a large jaw to say stupid things with.

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