An experiment conducted with worms, the results of which are published in Science, confirms the assumption that sexual reproduction allows re-mixing and gene exchange for compositions that allow one to stay one step ahead of parasites.
Biologists have been troubled for a long time and deal with the question - what is the evolutionary advantage of sexual reproduction? The existence of many shortcomings raises the doubt every time again because searching for a partner, attempts at solicitation, fighting with competitors, concern for offspring, all of these squeeze a lot of energy and even endanger life. In other words, sexual reproduction is full of disadvantages!
Asexual reproduction in which organisms clone themselves makes much more evolutionary sense: there is no need to search for a partner, no need for solicitation and seduction, no need to wrestle with competitors, which means a great saving of energy and of course no risk of contracting sexually transmitted diseases.
In addition to this, logic says that a creature that has lived long enough and has reached the time when it is ripe for cloning has proven that it carries excellent genes, so why should it "dilute" them with less good genes? And yet sexual reproduction exists and is common in most animals and plants, many biologists believe that the answer is... Parasites.
In nature observations, it became clear that creatures that "know" how to breed themselves tend to reproduce sexually when there are more parasites in their environment. What was missing was the laboratory experiment that would see and quantify the phenomenon, an experiment that would show the advantage of sexual reproduction in the presence of parasites.
Parasites create a situation in which, despite all the disadvantages of sexual reproduction, a creature has the advantage of mixing its genome with the genome of another creature, this is by sexual reproduction. Mixing the genome creates an offspring in which a new combination of genes, a combination that has a chance of being improved relative to the parents' genome, when there are parasites in the environment, the improvement is mainly expressed in resistance to parasite attack!
An experiment conducted with worms and the results of which are published in the journal Science gives a convincing answer and solution to the known problem and confirms an accepted assumption. According to the assumption: sexual reproduction allows re-mixing and exchange of genes for compositions that allow you to stay one step ahead of parasites.
Researchers from Indiana University used a roundworm Caenorhabditis elegans that is able to reproduce in two ways: sexual reproduction or cloning. The researchers "engineered" the worms into two groups, one group of worms that can reproduce only through sexual reproduction and a second group that can reproduce by cloning. Both groups were raised on a patch of grass where they harbored parasitic bacteria of the Serratia marcescens species, which invade the body of the worms, breed in them and eventually kill the worms.
After twenty generations it became clear that out of five different populations, worms that reproduced sexually continued to exist, while the clones quickly died and ceased to exist. Later, the researchers used two populations of parasites, one population that developed together with the worms and another population that was kept in the freezer, meaning that it did not learn the worms and did not develop with them. It turned out that the population of bacteria that developed over generations from the worms was more deadly than the frozen population, deadly compared to the cloned worms that did not develop resistance and became extinct. Whereas the worms that reproduced sexually (and developed in the environment of the bacteria) inherited and developed resistance and continued to exist. And so a laboratory experiment showed the researchers the correctness of a long-standing assumption.
The experience verifies and emphasizes a well-known and recognized phenomenon - the ongoing race between natural enemies: predators "learn to run faster and prey develop recognition skills, plants develop harder leaves and their eaters develop regenerating teeth, we develop medicines and bacteria develop resistance. A number of years ago, the biologist Leigh Van Valen defined the "arms race" between parasites and their carriers, between predators and prey, etc. and likened it to the words of the "Red Queen" from "Through the Looking Glass" (by Lewis Carroll) "in order to remain Instead, you have to keep running non-stop."
48 תגובות
Imagine what the human race would look like if everyone belonged to the gay class. Or in another way, does the group of the gays in society add or raise in any way the sexual reproduction in the world of the human race
Yigal c. and R. h:
Evolution is a very definite thing and it does not work between different species.
I refer you to Ronen Hazan's article:
https://www.hayadan.org.il/remarks-on-evolution-1905102/
It says there - among other things:
"In general, evolution talks about three processes:
A. Culture: duplication of details from each other.
b. Mutation: Replication is not error-free, so there are changes from time to time.
c. Selection: Changing environmental conditions or competition between individuals for limited resources result in the survival of the fittest.
"
This is indeed the case.
When only some of the conditions are met, evolution does not take place.
It is clear that natural selection exists, but it exists only because each species is part of the other's environment, but the effect of another species is not fundamentally different from other effects of the environment.
Since the other creatures are a dynamic component of the environment, co-evolution also takes place, but this does not change the basic fact either.
In principle, there is no point in talking about an advantage of animal A over animal B, just as there is no point in talking about an advantage of a car over a boat.
Yigal G., from Israel,
Obviously, evolution "works" (I don't think that's the right expression here, but that's what you used) both within a species and between different species. I assume that Mc*al means the mutation component that only happens in the individual and is passed on to his descendants. However, the other elements of evolution are affected between the species, the selection and the competition for resources are not limited to one species and there are many situations in which one species exterminates the other species or at least reduces it significantly.
Regarding an advantage, of course it is possible to tap an advantage in induction. If the marsupials in Australia, which were in the millions before the arrival of man on his companions, domestic and farm animals, rabbits, etc., were reduced to the risk of extinction, it is clear that they have no advantage over the other species. Of course, it's hard to put your finger on it and say it's because of the pocket, since it's the totality of their phenotypes compared to that of the new ones.
This presentation is a bit simplistic because there may be several situations in the biology of populations such as a steady state, cyclical behavior, the extinction of one of them or the extinction of one followed by the other as a result (e.g. predator and prey).
I guess the intention of M. R. And Camila's in "evolution works" was "natural selection works", since the other part of evolution, the formation of a variety of traits within the species through mutations and gene combinations, occurs all the time and does not "work". However, I disagree with their statement that sexual selection (evolution) works only within the species, since although most of the competition is between the partners of the exact same niche (food, predators-preys and breeding partners) there is considerable competition that also creates selection with other species - on Food resources and living space and towards predators-preys. Beyond that, there is a difference in the nature of the competition, and in any case also in the type of choice, between males and females of the same species (as is also evident from what I wrote in this discussion a few days ago). Hence, natural selection, which works as a result of competition between individuals of the same species, also works as a result of competition between individuals of different species.
Year:
I have to comment on two things:
1. A comparison between forms of reproduction is not a comparison between species. This is a comparison between mechanisms that serve the same purpose and not even necessarily in different species (as mentioned here, both the yeast and the hydra use both forms of reproduction depending on the conditions).
2. Even if the article were to compare species and talk about the advantage of species A over species B - it would be wrong. Evolution works, as mentioned, within the species. Evolution is based on "replicators" with small mutations and its considerations can only be applied within this framework. It is difficult to talk about species as replicators (it is possible, but it is rather forced).
In general, when there are two species living at the same time, regardless of evolution, it is difficult to talk about an advantage of species A over species B.
Advantage in what? They both survived. So one has an advantage in flight ability and the other has an advantage in strength. Which advantage is more advantageous? Everything depends on the circumstances of the future which are still unknown.
To those who answered my question, thank you,
I intended to write a comment on Camila's and Yuval's words above, and here Macal came and wrote a comment that I can sign (from 12.17:XNUMX p.m.).
But I have another comment. As for what Makal said (what about the promised numbering) that the article deals with the coevolution of bacteria and humans, after all, bacteria were evolving in the world over 3 billion years before coevolution with sexual animals began, and there is no reason that I know of to suppose that they would disappear if the sexuals disappeared.
Also, Machal's earlier claim that species should not be compared is mistaken, in view of the comparison that the article itself makes between the different forms of reproduction.
At the beginning of this comment page, I commented on what seemed to me to be a mistake - the use of the word "advantage" regarding evolutionary processes. Machal, as usual, answered in a reasoned way, and everyone can prefer what they see. In any case, the article claims, there is an advantage to sexual reproduction, although it limits the aforementioned advantage to protection against parasites - but bacteria also have parasites... and although they also have a kind of sexual reproduction, the essence of bacterial reproduction is not sexual.
Therefore, it seems to me that both my earlier comment against the use of "advantage" regarding evolution, and also the question I presented about the hypothesis of the advantage in the form of reproduction, stand.
Yair,
One of the most important differences in my opinion between those who reproduce sexually and others is the level of risk. In sexual reproduction, the "game" takes place between genes of the species, i.e. those that have already been proven to be probably "beneficial". Two couples of the same species "mix" their alleles to create new combinations and at the same time they maintain diploidy (two copies of the genome that are a backup for each other), which protects against recessive mutations, for example those that cancel the operation of a certain gene.
On the other hand, as noted by Mechael, lateral transfer is not "ordered" and the source of the DNA can be from any nearby production. Beyond that, as organisms that are usually haploid (having one genome), bacteria are exposed to the effect of any mutation.
In short, those who reproduce sexually are solid investors, while the germs invest in oil stocks and options, who profits more? 🙂
Friends:
Regarding teleology: it is advisable to occasionally mention the fact that evolution is not teleological - but it is advisable to do so only when you think that someone really thinks it is teleological.
Yair has already been responding here long enough for us to know that he does not attribute a teleological goal to evolution and that his use of the word "goal" is just a convenient shorthand - one that is used even among professional evolutionists when they are sure that everyone knows what is meant.
In such cases it is appropriate at most to specify the intent of the expression (as Camila did) without attributing a misunderstanding to the user.
One more thing about bacteria:
Presenting the bacteria as devoid of sexual reproduction can be misleading.
As shown here, the contribution of sexual reproduction is that it makes better possible new combinations of genes that exist in the population.
Bacteria also have a mechanism that allows this and it is the mechanism of the horizontal transfer of genes from one bacterium to another - a transfer that even crosses the boundaries of the species.
Such a transfer is very rare in multicellular organisms because it is not enough for the new genetic load to reach any cell of the production cells: it must reach a germ cell (and not just a germ cell, but one that will get to participate in the creation of the next generation) and sexual reproduction developed in multicellular organisms as a "substitute" for the horizontal transfer of genes (And I know that the word "substitute" also has a teleological meaning, but I hope you will apply what I said in the first paragraph).
Yair
Your question is problematic, at least for the following reasons
First, you present a teleological assumption, and such assumptions are out of place in the science that deals with causes and effects. In philosophy there are many discussion forums that take this claim seriously, and I recommend you to search there. And if you want, theology is based on such claims, and there you will find many answers, each of which is better than its name.
Second, let's assume, for the purpose of the academic discussion, that there really is teleology in biology. Let us understand that Rabia has a purpose. Well, the advantage of one breeding style over another is still unclear and depends on niche conditions. Therefore, each case must be examined individually.
withering:
It is clear that the different species influence each other, but the way I interpreted Yair's question it resembled R.H.'s claims from previous debates.
R. H. debated the question "Does consciousness give humans an advantage over bacteria that do not have consciousness?"
And in the same way - at least that's what I thought - Yair asks, "Does sexual reproduction give its owner an advantage over bacteria that don't have sexual reproduction?"
One of the reasons for this way of interpreting the question is that the question regarding the co-evolution of bacteria and humans was addressed in the article itself and it is not possible for the person who read the article to ask it.
To the question as I understood it, my answer is correct.
Mr.
I don't agree with you,
Evolution does work in a population of the same species, but different species participate in it by virtue of being part of the environment of a given species. They are part of the forces of selection if you will, because of competition for resources, because of predation, parasitism, etc. In addition, I see no reason why not to compare evolutionary processes between different species with defined variables, such as the rate of mutations, the rate of splitting into species over time, the degree of closeness to the shape of the ancestor (that is, the degree of preservation of the original "model", which in itself can be a good measure for the success of that model, because it is necessarily a durable model that has survived many changes and diverse selection pressures, which suggests its good chances to withstand future changes).
Yair,
A) I use your question to emphasize that reproduction, like evolution, has no goal or purpose. I'm sure you didn't mean that even though you used that wording. Reproduction (any reproduction) is simply the mechanism that enables, although does not require, the continued survival of the species. The comment is intended for those who still do not understand this and believe without reason or need that there is pre-planning or a deliberate hand here.
b) The fact that a great many organisms that have come so far multiply by reproduction in various forms with most of them thriving, should already make it clear to you that your question is not well defined. If you ask about specific variables it might be easier to start answering the question for those variables (eg number of offspring, maybe the diversity of species, maybe a correlation to the complexity of the organisms, ability to deal with changing conditions). It's a bit like asking which way to Jerusalem is the best when your measure is just getting to Jerusalem... this question only has meaning if you refer to specific variables such as the duration of the trip, distance, the amount of fuel/energy needed, etc.
Year:
Since evolution always occurs within the species - there is no logic in comparing "a species with a non-species".
By the way - bacteria survive less well than stones.
I am asking the biologists and anyone who thinks they know enough to answer the question that remains unanswered for me: assuming that the purpose of reproduction is to preserve the species, do those who reproduce sexually survive better than bacteria?
Yigal C:
No.
I don't agree.
I just don't see any point in repeating the same things over and over again.
In my opinion - you didn't even think I agreed and wrote your last comment just to bother.
Mr.
I just turned to answer.
Since you did not raise a single argument against one, and since you announced that you knew all the things even before the discussion, I assume that you hereby agree with my words, and consider this the end of the discussion.
Yigal C:
You still haven't said anything new - neither in relation to what you said before nor in relation to what I knew before the discussion - so my answer remains as it was
Mr.
I just turned to read your comment.
Since we concluded that in the first generation, there are more occurrences of genes of males investing less than genes of any other individual in the population (and you stated that you knew this before the discussion began), we can continue to discuss the second generation: these genes are again more distributed than genes that do not carry the investment trait the lesser of the males, and this time they are also propagated through the females who are the offspring of such males. Here also appears the advantage of the genes of the female who invests more: they are also spread more thanks to the ability of the males to reproduce with more females. And this is a much more fundamental reason for the rooting of sexual reproduction than the resistance to pests of all kinds.
Yigal C:
You didn't say anything new and I knew what you said even before the discussion and my answer remains as it was.
M.
There is a big miss here of the main point and the discussion is dragged to the sidelines for nothing.
The important point is that thanks to the ability of males, who invest little in the sex cells and pregnancy, to multiply more females, they spread these genes to many offspring (more than those who reproduce with only one female). In doing so, they propagate the feature of sexual reproduction that has no equality in the parental investment of both parents. Since this trait has a positive effect directly on the distribution of genes and among them on the distribution of the genes that determine this trait itself, it spreads easily in the population.
Note that not only do the males that carry this trait create more offspring than the average number of offspring of individuals that do not carry this trait, but that since the amount of these males increases in the population, there is a greater chance that they will reproduce and pass the trait on. Likewise, the females among their offspring also carry this trait and pass it on to their offspring.
And another point: natural selection will manifest itself in the aspect of protection against diseases and parasites, only in times of crisis, while in the aspect of the advantage in question here, it manifests all the time.
Regarding the initial appearance of sexual reproduction, there are quite clear hypotheses that can also be discussed.
In yeast the situation is a little different, during starvation the diploids undergo sporulation and form haploid spores which will then undergo haploid divisions or mating between the a and alpha pairs to create new diploids.
jubilee:
I talked about mutations only in response to a question that does not really belong to the article.
In topics related to the article, I talked about combinations and re-combinations, which is exactly what you just said.
R.H.:
The hydra switches to sexual reproduction precisely in times of crisis.
http://en.wikipedia.org/wiki/Hydra_(genus)
In general, sexual reproduction that increases the diversity seems to be preferable precisely for the purpose of dealing with crises where - when the diversity is high - there is a greater chance that among the different ones there will also be some that are adapted to life in the conditions created by that crisis.
The article talks about exactly that - that is - about using sexual reproduction to deal with parasites (which without a successful deal would create a crisis).
I think what Shigall means, and correct me if I'm wrong, is an alpha male situation where only one male squares all the females and the other males don't participate in the game. Then there is no comparison between the distribution of his genes and theirs, but the distribution of the females' genes is equal.
In any case, the main advantages of sexual reproduction and the closely related diploid genome are:
1) Creating a situation of at least two alleles for each gene and masking mutations.
2) Mechanism of lateral transfer within the species of alleles.
3) Mixing and creating new alleles by the homologous recombination that occurs in meiosis, and therefore cloned animals (or for that matter consanguineous marriages) is something that lowers the genetic diversity and leads to sensitivity to changes such as infection by pathogens and an increase in the incidence of recessive genetic diseases.
4) Since the partner in many cases is not immediately available, sexual reproduction ensures that only those who are fit and able to survive and obtain partners in competition with other males/females will reproduce, meaning that there is selection.
The disadvantages of sexual reproduction are manifested in times of severe crisis, when the chance in the population of those with haploid genomes that express the mutations and do not mask them will be a mutant that will survive is higher. Such things have been demonstrated in yeast that can be haploid and diploid and in worms in the present paper.
Yigal:
What you said now - I said it before.
See here:
https://www.hayadan.org.il/sex-as-we-know-it-works-thanks-to-ever-evolving-host-parasite-relationships-0711/#comment-300314
Read and see that I was talking about another arena of competition and I didn't just use this expression, because in the competition there are also losers - males who don't get to mate at all.
Read more and see what I said about the possible correlation between this arena of competition and the arena of life in general.
Generally - it is clear that contrary to what you said - this is not an important reason for the existence of sexual reproduction in nature because in order for it to affect the survival of the species (which is questionable in itself and as I have already said - there are also quite a few monogamous species) many years of evolution are necessary within the framework of sexual reproduction and therefore It cannot explain the existence of sexual reproduction but at most say something about the patterns of behavior within it.
Michael mentioned mutations. Apparently, there is no connection. However, sexual reproduction is a mechanism that in a certain sense imitates the creation of mutations. It does not create new mutations but replaces existing and successful mutations.
The absolute majority of organisms do not have a permanent partner and in most cases a significant part of the males do not get to reproduce, therefore there are males (and not females) that produce more than one launcher. The female can conceive once in each reproductive cycle while the male can reproduce many times in such a cycle. In any case, the whole matter of establishing unequal sexual reproduction belongs to primitive creatures in the distant past and should be thought of as such. The organisms that exist today inherited this reproductive strategy from their predecessors. The advantage that such an arrangement of genes has in relation to the extent of their distribution is the one that maintains this situation in the vast majority of organisms.
It is true that almost every mating involves one male and one female, but as stated above, the male can participate in many fertile matings and the female in only one.
Yigal:
It is not a belligerent tone but a tone of someone who feels that they are corresponding with him without reading his words.
In my previous response I wrote: "females" by mistake.
Read "males" instead.
It is worth understanding that in a given situation where there are a similar number of females and males, and they all mate - some with one partner and some with more - the number of matings of females with someone who is not their permanent partner is equal to the number of matings of males with someone who is not their permanent partner.
This is because in every such mating one male and one female participate.
Mr.
First, please reduce the aggression - I am not interested in a heated argument or one that does not concern the matter itself.
Second, I did not claim that more genes of female origin were distributed, but that more genes of male origin were distributed.
Third, if a particular male reproduces with more than one female, his genes appear in more offspring than any other individual (male or female) that reproduces with only one partner. Since the number of offspring of each female is limited by her ability to create them, the number of offspring of each female will necessarily be smaller than that of any male breeding with more than one female.
If we agree on all this and you still think I don't understand, I'm ready to continue this line of logic with you.
In all my words I never once claimed that my words refer to the advantage given to those who reproduce through sexual reproduction. My claim is that in the particular sexual reproduction (in which there is no equality of investment on the part of the two partners) used in most existing organisms, the ability to spread this trait in the population is built in more than in the other forms of reproduction.
The matter of the prisoner's dilemma does not belong here, and when all the males are polygamous, some of them benefit at the expense of the others.
Yigal:
I explain, and repeat and explain, and you say you understand - but you don't.
Each offspring of the first generation has the same number of genes from a female source as from a male source, so how can it be argued that more female genes were distributed?
Answer to the above question: By mistake!
It is true that this is a situation that encourages males to polygamy, but it does not contribute anything to the species (beyond what I have already mentioned).
Of course there is a typical case of the prisoner's dilemma here because when all the males are polygamous none of them gains anything but it is a state of stable equilibrium.
In any case - nothing of what you said belongs to the explanation of the advantage of sexual reproduction, even though your initial claim was that it is a more significant explanation than the one given in the article.
withering,
I mean the inequality in investment between spouses and children. The males invest in their gametes less than the females and therefore can breed with more females and spread their genes more than them. Built into this feature is the ability to be more distributed in the population.
M. R.
If a male reproduces with more than one female (which is a very common situation in nature) then he spreads his genes more than his partners. Hence, in the first generation, all offspring will carry the genes of their parents and their ancestors, but some fathers, those of the type that invest less in the sperm cells and can therefore reproduce with more than one female, will have more offspring. The males among these offspring will carry this trait and spread it further in the population in the second generation as their ancestors did, but the females among these offspring will also carry this trait and pass it on to their male offspring and so on. In this way, the trait of sexual reproduction with unequal investment in the offspring (both in the gametes and in the pregnancy) will spread very quickly in the population at the expense of other forms of reproduction (non-sexual and egalitarian sexual).
Igal,
Do you mean the inequality created between individuals of the same pair following the attribute of the change in the degree of investment?
Yigal:
I don't know what you want, but no species can spread its genes more than the other (not even in the first generation).
That was your starting point and it is wrong.
I didn't see any additional claim in your words, so what exactly are we arguing about right now?
I mean that later on (after the first generation) some of the females also carry the trait of unequal sexual reproduction.
The fact that the genes from both couples are equally common in the first generation is irrelevant because the females also carry the trait of unequal sexual reproduction. This trait spreads through the population (and even at a rapid rate) since males who carry it breed with more females than those who don't.
All other things are not relevant to the topic.
Yigal:
Something else I meant to write and forgot:
Another thing happens:
Another arena of competition is added - the arena of competition for spouses.
This can, to a certain extent, stimulate natural selection and perhaps even improve it to the extent that there is a correlation between the ability to compete for mates and the other survival abilities.
Yigal:
The total amount does not change and therefore - on average - genes from the mother are not less common than genes from the father.
Each offspring has the same number of genes from the mother and genes from the father.
This is what is important in the context of what you said at the beginning.
What does happen is that more combinations are created - and this is what is explained in the article.
The many combinations are created - both by the randomness in the way the sperms and eggs are created and by the randomness of recombination between them at the time of fusion.
The division of roles between male and female affects - if at all - only the randomness of the fusion (because in addition to the above-mentioned randomness, the randomness of the fertilizing partner is also added) and therefore the diversity among members of the species - but not the distribution of genes.
It is not clear if this additional randomness is necessarily beneficial and therefore there are both monogamous and polygamous species in nature.
And more:
Do not think "humans", with the arrangement of male-female couples, important animals, where usually single males violate most of the females.
And in your opinion:
Way A: The number of male parentage does not equal the number of female parentage - there are some males who have more than one parentage and probably in generation zero the average (only) will be equal;
Way B: Suppose that in the population you presented there is only one male who invests less and suppose he succeeds in reproducing with only two females. He already has more pregnancies in the population than any other individual and in the first generation there will already be two littermates carrying the said genes and the continuation is clear.
And one more thing, the efficiency of the paired method is at least equal to the non-paired one and may even exceed it.
Mr.,
Indeed, the total amount does not change, but only the frequency of occurrence of unequal sexual reproduction: the number of males and females carrying the trait increases thanks to the ability of the male carrying these genes to fertilize more females.
Yigal:
The reasoning you present seems wrong.
The males can no longer spread their seeds and this can be seen in several ways:
Way A: Each offspring has two parents - one male and one female.
The number of male "parentages" is, therefore, equal to the number of female "parentages" and this means that each male has on average the same number of offspring as each female.
Way B: The number of parallel pregnancies in the population is blocked from above by the number of females.
This way also points to the inefficiency of the couple method.
If there are 2X individuals in a certain species, then if it is X males and X females, only X pregnancies can exist at the same time.
If the same species has only females (and it reproduces without sex) 2x pregnancies can exist at the same time (although boring and devoid of the fun we know, but no less fertile)
Although achieving equality in the competition against parasites and pathogens is extremely important, in my opinion the great extent to which sexual (sexual) reproduction is widespread among life on earth is rooted in a much more fundamental reason: the possibility that one of the species can invest less and be "easy to move" in terms of reproduction, allows it to spread his genes extensively. On the other hand, his partner must invest more to compensate for the lower investment of the first. Seemingly, there is a loss for the greater investor, but the fact that among the joint offspring there will also be those from the less investing species (males) also gives the member of the more investing species (females) an advantage, since his genes, which appear in his less investing offspring, will also be widely distributed. In this unequal sexual reproduction, is built the feature that causes it to spread widely.
I assume that other techniques exist and were even developed in the past that made it possible to achieve resistance to pests, but the juxtaposition of the technique of mixing the genes in sexual reproduction to achieve resistance to the widespread distribution of the genes of the less investing couple tipped the scales in its favor.
Different mutations change the characteristics of the animal whose genes they affect.
Most of the time the change is for the worse and in the animal the cell from which the mutation began to develop becomes extinct.
I definitely think this can be called a disadvantage.
So what about in the opposite direction?
You have to remember that there are many directions and not just the opposite direction.
There are mutations that have no effect at all.
They are not in the opposite direction and there is no reason to define them as an advantage or a disadvantage.
There are, however, mutations that give a real advantage.
If the mutation gives the animal higher speed or more strength without affecting any of its other characteristics, there is no doubt that an advantage has been created. In fact - this is an advantage that will eventually cause the entire species to change because the carriers of the mutation will defeat their brothers in the reproduction race.
And what about mutations that allow the animal to take advantage of resources that its parents could not take advantage of?
They are also usually an advantage and there is a chance that you will conquer the entire species.
A mutation of this type occurred in humans recently (in evolutionary terms) and it allows some humans to digest lactose even in their adulthood.
This mutation is gradually conquering all of humanity.
There are situations where a mutation moves the animal to another niche.
Some time ago an experiment was described here in which we encouraged yeast to become multicellular.
They were identified by the fact that they sank in the liquid while their brothers remained in suspension.
This is an example of moving to a different niche with different food sources.
Here it is difficult to talk about a real advantage, although if it is a relatively free niche where the competition for resources is less intense - it can be an advantage, but not an advantage over the non-mutant brothers because the transition to another niche canceled the competition with them (in the opposite case of reaching a busy niche, This may also be a disadvantage and the animal will become extinct).
In my opinion, not many mutations happened that moved animals to another niche at once.
Usually there were intermediate stages where at a certain point a reproductive separation was created between them and the original species - either because of a physical barrier that was created or because the new niche was so tempting that those with the ability to exploit it no longer bothered to return to the original niche.
In such a situation, there is an advantage (or at least no disadvantage) in losing the features that allowed the animal to live in the original niche.
In the end we find in each niche animals that are able to exploit its resources.
In this niche they have an advantage over other animals (which may have an advantage in their niche).
In other words, this is a context-dependent advantage
And yet the word advantage seems appropriate to me. At the moment I'm pedaling in a gym, so I'll give details later
Machel,
I meant "advantage" as an explanation for evolutionary processes, which are always ad hoc. It doesn't seem to me that the phrase "advantage" has any real explanatory power regarding evolution, but rather an explanation of an opinion, and as I wrote, those changes that are considered in people's estimation as an "advantage" can be better explained through adaptation, which is neutral, not an assessment of nature.
The last part of your answer is acceptable to me.
Phenomena like you brought about fish can be found in masses.
The word advantage does not indicate anything teleological.
When a company is looking for an employee and says that English proficiency will be an advantage, it does not make the intended employee learn English - it appeals to people who already speak English.
These people find themselves in a situation where an advantage is created for them without their intention.
Even when a public relations office gives an advantage to those who have a good external appearance, it does not cause the good external appearance of the employees it recruits.
An advantage can be created by force of circumstances without any purpose.
It is true that in every evolutionary development it is correct to see "advantage" in the simple sense of the word.
Certain fish developed lungs and were able to adapt to land.
Later they lost their gills (which became unnecessary to maintain), but after eons of living on land some of them returned to living in the sea - this time without gills - which forces them to come up to the sea surface every now and then to breathe air.
So what is better? Live at sea or live on land? And if living in the sea - is it better without gills?
So that's it - it's not necessarily about absolute advantages, but an advantage in a very special environment that makes it possible to penetrate another ecological niche, process another type of food, and the like. An advantage in another environment may be a disadvantage in another environment and everyone knows the example of sickle cell anemia where the tendency to get sick is usually a disadvantage but in a malaria stricken environment it is actually an advantage.
The article is interesting, but talking about an "advantage" in evolution is wrong even though many good people use it.
1. Attributing an "advantage" to a feature is always teleological. He attributes to the series of changes that led to the creation of the current feature "intention".
2. Every change modifies an existing feature that was also up to now in possession of an "advantage", that is, attributing an advantage to a feature has an internal contradiction.
3. Every change should be discussed within the framework of adaptation, which is a central engine of evolution, and also every "advantage" corresponds to the processes of adaptation.
4. In the end, a theoretical "advantage" is nothing more than a third grade: an advantage. Feature B is an advantage, feature C is an advantage, the pedagogical committee decides: the creature survived.
A similar article by Lotem Eliyahu
https://www.hayadan.org.il/why-sex-0311093/
At the beginning of the article, examples of the disadvantages of sexual reproduction are given.
".. the existence of many shortcomings raises the doubt every time again because searching for a partner, attempts at solicitation, fighting with competitors, concern for offspring, all of these squeeze a lot of energy and even endanger life..",
I wonder if these shortcomings are relevant to the "worm society".
If these do not exist then the weight of the advantage in sexual satisfaction increases in the balance of advantages/disadvantages.