I’m still not getting it, eh? Well, let’s look at what you are saying.
The basis of all that you just said is the notion that being male is inherently a sweet deal evolutionarily because the females do most of the reproductive hard lifting, and males could be out there boinking every day making babies while the female is pregnant. This notion, though superficially appealing, is simply false at equilibrium sex ratio, and well known to be false among evolutionary biologists. I don’t mean that the part about the hard lifting is false; it’s true in many species, and that fact is important to many questions other than this one (this is differential parental investment, which must not be confused with total investment, which in the population is equally allocated between male and female functions). But the part about the hard lifting meaning that it’s a better strategy to be male is false at Fisherian sex-ratio equilibrium. In fact that’s the essence of sex ratio equilibrium, and it holds however the equal investment in male and female functions is achieved. The fact is that males (or “male function” where hermaphrodites are concerned) as a whole cannot have more offspring than females as a whole, given that every offspring has exactly one mother and one father.
Your reasoning would seem to say that in a population with separate sexes in a 1:1 ratio, the average male has more offspring than the average female. After all, he can be out there mating every day during that nine months when she is pregnant. So he will have, according to you, 270 children to her one. Sweet deal. In fact you should argue that, given the great advantage that males have, the population will evolve to a highly male-biased sex ratio. Of course this is nonsense. Where would the mothers of all these “extra” offspring come from? Established sex ratio theory has it right: males have no more offspring than females given a 1:1 ratio, and that is the equilibrium ratio. Of course males would “like” (evolutionarily speaking) to impregnate a new female (or hell, why not several?) every day, but they cannot, on average, possibly succeed at this, with all those other males around at that critical 1:1 ratio (when males are rare, sure, just like when females are rare females have an advantage; that’s what leads to the 1:1 ratio).
In a hermaprhoditic population an individual on average has the same number of children through male function as through female function. Your reasoning would seem to say otherwise, but it’s incorrect for reasons analogous to the above.
So what about that rare male in a population consisting almost entirely of 1:1-investing hermaphrodites? Well, say that in a given time period, or better, over a lifetime, a hermaphrodite is the mother of n offspring and the father of n offspring, for a total of 2n offspring. The rare male shuts off female function and doubles his investment in male function. If the payoffs for investment are linear, he is the mother of zero offspring and the father of 2n, for a total of 2n offspring, just like the hermaphrodite. QED.
Now, one can consider what happens when payoffs are not linear. In fact this is how evolutionary biologists usually approach the question of hermaphroditism. You can imagine that, in species with gestation, being pregnant interferes with going out and boinking, which leads to a certain curve being convex, which leads to the evolution of sexes, but this is just the specialization argument (and you can’t get a factor of 270; at most there’s a factor of two). Or you can imagine that, for example, some scarce resources are more useful for male function and others for female function, so that that curve is concave and it makes sense to be a hermaphrodite. But that’s not what you’re arguing.
Blake, you’re all over the place. First you were imagining that in a hermaphroditic population there would be much more investment in female than male function. When I pointed out that this was incorrect under simple sex-ratio theory, you patted me on the head for being aware of Fisherian sex ratio theory, as though I had taken a misguided step toward understanding your point rather than pointed out the gaping hole in your logic. Then you went on to demonstrate a complete lack of understanding of sex ratio theory. This is all well-established stuff in the literature, so I’m not going to spend any more time trying to talk individuals out of common misconceptions. If you are going to indulge in condescension, I think you will find that you are more successful when you have a basic grasp of the subject at hand.
Josh I really can’t see why you are having such a hard time with such a simple concept. I have given you an example that proves beyond any possibility of argument that a cheating male in a hermaphrodite population has a 100-fold increase in reproductive capacity. If you dispute that example can you please explain clearly and concisely why? If you don’t dispute that example then I can’t see how you can fail to understand that evolving a separate gender is an evolutionary advantage.
The trouble is Josh that you have clearly read Fischer but not understood Fisher. For example:
That is simply nonsense in the evolution of separate sexes from a hermaphrodite population. In that situation the Fischerian ratio is not applicable because, as you yourself said, “Fischerian sex ratio theory predicts a 1:1 allocation of resources, but allows that to be achieved by either a population consisting of separate males and females or a population consisting entirely of hermaphrodites making equal male and female investments (or by various other configurations, including populations containing both hermaphrodites and non-hermaphrodites)”. In the development of separate sexes WE DO NOT HAVE A POPULATION CONSISTING ENTIRELY OF HERMAPHRODITES MAKING EQUAL MALE AND FEMALE INVESTMENTS.
Josh had you understood Fischer you would relalise that the whole premise is based on a zero sum game. If either sex increases beyond around 60% the opposite gender automatically becomes a limiting resource for the species and simply being that minority species becomes an evoutionary advantage for that reason. With the evolution of chetaing males the zero sum game is altered.
Males have a huge reproductive advantage and so they proliferate and only after they make up more than 60% of the population does it become advantageous to be female. But under those circumstances the advantage of being female is only achieved because ova are a limiting resource. Sperm are not a limiting resource when over 60% of the population are cheating males. Because only ova are limiting only the production of ova is an evolutionary advantage when the sex ratio becomes unbalanced in this way, production of sperm is at best reproductively neutral. That is going to favour those individuals that only invest energy in producing ova, and we then have distinct genders.
And this is the very simple concept that you fail to understand despite me stating it quite clearly several times. Where the hell did I say anything like that about “a population with separate sexes in a 1:1 ratio” Josh? Please provide a quote. You are confusing yourself on a simple issue by trying to extrapolate to irrelevancies rather than making an effort o understand the exmaples given. Don’t worry about what happens “in a population with separate sexes in a 1:1 ratio” A population with separate sexes in a 1:1 ratio is what we are trying to arrive at, not what we are discussing.
My reasoning doesn’t say anything remotely like that. What my reasoning says is that in a population consisting pirmarily of hermaphrodites , the average male has more offspring than the average female. That is all that I hav ever said.
Nonsense. Absolute nonsense. My reasoning doesn’t say anything of the sort. My reasoning says that in a hermaprhoditic population an individual on average has the same number of children through male function as through female function, but that a cheating male has children only through male function and as a result has more offspring. If you believe that you can reason otherwise from what I have said then show us the reasoning and let us discuss it. If you have reasoned to any oth rocnlsuion then you have applied seriously flawed logic, which is why you are struggling to undertsand a simple concept.
QID. Quod ingnoranti demonstrandum.Your logic is flawed from end to end.
In a given time period, or better, over a lifetime, a hermaphrodite is the mother of n offspring and the father of n offspring, for a total of 2n offspring.That much is true, but after that you shift to a complete non sequitur.
You have confused paternal offspring with paternal investment Josh. Those are two very different things. In our population an organism will indeed produce as many paternla offpring as maternal. However the investment in the maternal offspring is much higher. It might help you to consider the fact in modern humans men and women have excatly the same number of children from a partnership. However the physiological invstment by the male consists of a few mL of sperm whiel the investment of the female consists of millinos of calories, phsyiucal injury and a period of near incapacitation.
Josh you really need to undertsand that just because the ratio of offspring from any given gender will be equal that does not mean that the investment required to produce those offsping is equal. It takes far more energy to carry a child than to ejeculate. Now that you hopefully undertand that we will proceed with the rest of your argument with that in mind.
As the exmaple I gave above proves a chetaing male can produce almost 100 times more offsping by simply shutting off his femlae function without even needing double to his male investment. By producing exactly the same number of sperm he will produce 100X more children than a hermaphrodite.
Josh I will re-post my example, and I wll ask you to state clearly whether you agree that the example is a valid approximation of what would happen with one cheating male in an hermaphroditic population.
Use a hypothetical population of hermaphroditic humans where every mating results in both partners being impregnated. Assume that all individuals mate every day until impregnated. Introduce one gene causing maleness. That gene will be replicated at every single mating because that individuals partners will all be impregnated. A hermaphrodite will fall preganant after mating and wil be unable to mate agin for 9 months due to pregnancy, but the individuals carrying that maleness gene will be able to continue to mate every day for 270 days (9 months) following mating. IOW a gene causing maleness will be able to reproduce 269 times for every one reproductive act of a hemraphroditic individual.
Do you see a problem with that example for what would happen if a cheating male evolved in a population of hermaphroditic humans Josh? If you do see problems please state clear;ly what they are. The simple fact is that if that example is logically valid then that proves there is an evolutionary advatage to being a cheating male.
No idea what you mea by this Josh. The investment line’ has only two points, male investment and female investment. Two points can’t help but be linear. However being linear does not enable you to conclude that the outcom will be the same. The mistake you are making is that you are assuming that in a hermaphroditic population an organism invests the same number of calories in producing ova as it does in producing sperm. That isn’t true and that is why you can’t understand why being a cheating male works.
Let’s assume an hermaphrodite invests 10X more calories to produce eggs than it does to produce sperm. That’s a ridiculously low multipliere becase ova are expensive while sperm are cheap, and it only takes half a dozen functional sperm to fertilise each egg at eachmating. In fact organsims can produce millions of sperm for every ovum and still invest orders of magnitude fewer calories in sperm production. Therefore an organism that shuts of female investment is not simply able to double the male investment, he is able to increase the male investment 10-fold.
I wasn’t imaginging that, that is a biolgical fact. The weight of the ovaries in most hermaphroditic organisms are orders of magnitude larger than the testes and the caloric investment is comparably higher.
Josh you really haven’t understood Fischer nor have you understood what I have posted quite clearly. I will sy it again, and please if you don’t understand it this time then tell me and I will elucidate. You are corrcet in your understanding of Fischer in that so long as nobody is able to cheats it is possible to have “a population consisting entirely of hermaphrodites making equal male and female investments”. But as the examples I gave above demonstrate as soon as one organism cheats by becoming exclusively male we no longer have “a population consisting entirely of hermaphrodites making equal male and female investments”. What we then have is a population consisting eprimarily of hermaphrodites making equal male and female investments but with a small subset of male cheats who are at a significant evolutionary advanatge.
Pointing out the expected investment ration in either a population consisting of separate males and females or a population consisting entirely of hermaphrodites making equal male and female investments is not in any way relevant to what we are discussing because we are discussing a situation in which we do not have hermaphrodites making equal male and female investments, by definition. That is the gaping hole in your logic. You are confusing stable populations with the circumstances that led to those stable populations.
Well if you believe I have misunderstood something then point out cleraly where that misunderstanding is. Simply saying that I have misundertsood it is pointless.
Josh it really isquite simple and I teach this stuf to ndergrads without any difficulty, I can’t see why you struggle. If the exmple I have given is true it PROVES that being a chetaing male has a huge evoloutionary advanatge.
Frankly Josh I think that you have read a little of Fischer’s work and failed to understand it. Fischer himself said quite cleraly that investment in either sex within a population of hermaphrodites is only equal under conditions of high sperm competetion. Fischer was well aware that in conditions of limited sperm competition such as in slugs or hermaphroditic humans the investment in the production of sperm is orders of magnitude lower. Why in Og’s name would you think that a hermaphroditic human would invest as much energy in producing thousands of litres of sperm as in producing a baby? That’s just stupid. A few litres of sperm during alifetim is all that ois required, why would such an organsim invest equal energy in producing thousands of litres for every child born? What snse does that make to you?
I think Josh that once oyu understand that fact and escape your ignorn belief that investment in each sex is always equal you might just understand this very, very simple concept.
Um, Blake, I hate to break it to you, but you’re the one who doesn’t understand basic sex ratio theory. No, you didn’t discuss a population with separate sexes in a 1:1 ratio. I was demonstrating how your reasoning would lead to conclusions that we would presumably agree are false. I was also trying to emphasize that a male has no advantage when the population is making equal investments in male and female functions. This is true whether that equal investment comes from equal investment in separate males and females or from hermaphrodites. And in a hermaphroditic species one expects a 1:1 sex investment ratio. You seemed to have admitted this, but now you seem to have gone back on it. That you think otherwise shows that you do not understand basic sex ratio theory.
It doesn’t make sense for me to spend any more time trying to convince you of anything (Unless, of course, you are willing to wager a large sum of money, in which case we can take the question to agreed-upon experts for adjudication. Actually I would love for you to e-mail, say, Ric Charnov about this; he will explain to you that you don’t know what you are talking about). So, I am going to unsubscribe from this thread, and leave you to go on about how wrong you think I am in my absence. It’s a pity that you would be teaching this sort of thing to anyone.
I always knew that biology major would come in handy…
Fisher’s sex ratio is the observation that the number of offspring produced is a 1:1::male:female ratio. Not that there is an approximate 1:1::male:female ratio in the population. If the sex ratio, the ratio of the sexes of offspring, is upset, the favored sex will quickly dominate the population. Yes, the minority sex will have an easier time finding mates- but their offspring will still be born at the unequal sex ratio and the majority sex will continue to dominate the population- even though many of the majority sex fail to find a mate. Fisherian logic states that any mutant that can produce a greater ratio of the minority sex in their offspring will have an advantage. Since the genes to produce more of the minority sex are more likely to be carried in the minority sex, and the minority sex has a situational advantage, the male:female ratio of the population returns to parity (and probably overshoots, and we have the whole deal again, just the minority and majority sexes are reversed). Equilibrium is eventually reached with the 1:1::male:female offspring ratio we observe. Important point: the offspring ratio is a mass action, statistical beast- it is not necessary for individual organisms to have a 1:1 sex ratio.
I think Josh dePlume is confusing the “male/female biological investment” Fisherian reasoning talks about (offspring) with the “male/female biological investment” mentioned regarding hermaphrodites (sperm and ova). Though I do agree that hermaphrodites make equal biological investments in male and female offspring: none at all… their offspring are hermaphrodites.
When the mutant “cheater” first arises the sex ratio of its offspring would be determined by whatever the heritability rules the mutant allele followed, since there would have been none of the Fisherian feedback to adapt it. Nor would there be until the hermaphrodites became the minority sex.
The problem is Josh that you didn’t demonstrate any such thing. You asserted that my reasoning would lead to such conclusions, an assertion that was challenged. But this is the SDMB Josh, not your HS lunch room. We know the difference between a demonstration of a point an an assertion of a point.
All you have done is asserted, and since I have challenged the assertion it is now up to you to show the evidence or reasoning that justifies to that asssertion.
The problem is Josh that we were never discussing a situation where the population was making equal investments.
Please enlighten us Josh. How can a hermaphrodite population be making equal investments in male and female functions when femlae function consumes well over 100X the calories within the population?
How many times have we seen this at SDMB? Admitedly normally it’s in GD, rather than GQ.
Josh when you refuse to answer simple questions it’s quite obvious that you wish to remain ignorant. We know the answer to you questiona nd can explain it to you in painful detail if you wish us to, but you need to clarify excatly what it is you don’t undertsand about the examples and data presented. If you can’t do that it seems that you wish to remain ignorant.
I’ve said it before and I’ll say it agin. We can help the ignorant, but the willfully ignorant are beyond the aid even of Cecil himself
101000etc.
Fischer did a lot of work on sex ratios. You’re right the Fischer sex ratio is the observation that the number of offspring produced is a 1:1. However Fischer also published the stuff that Josh seeems to have half understood, which stated that there will be equal effort put into success in male and female reproduction, even amongst haermaphrodites. What Josh doens;t understand is that it doesn’t require equal effort to be succesful in male reproduction in conditions with limited sperm competetition.
Blake, you stated that most hermaphrodites put more effort into female function than male function. But I still don’t understand why this should be the case.
Let’s take a simple example. A population of hermaphrodites. They shed their gametes into the water. Sperms swim around until they meet an ovum. In a case like this, wouldn’t there be equal total investment in sperm and eggs? In this case there really is an advantage in producing liters of sperm, right?
You say that it is the case that most hermaphrodites invest more in female function than male function. If there was a big advantage in shutting off female function and concentrating on male function, then it seems that there would be no reason at equilibrium for a hermaphrodite to invest more in female function than male function. The larger the advantage in being male, the more a hermaphrodite should invest in male function, right?
In the example you give, of organisms with mammal-like reproduction, your hermaphrodites are obligated to spend much more on female function than male function. But why would they do this? If male function takes only a small investment of energy, why is it a valid assumption that pregnancy would interupt male function?
What I don’t understand is why a hermaphrodite would spend less or more effort on one function, when a gendered species spends (at equilibrium) equal effort on both functions.
Lemur if you read the entire thread you will note that what I actually said is that hermaphroditic humans and hermaphroditic slugs put a lot more effort into female function, not species that ‘shed their gametes into the water’. Truly free-spawning species that just shed their gametes at random into the water column do tend to put equal effort into both functions because the water column represents near total sperm competition. However we are here talking specifically about what occurs “in conditions of limited sperm competition such as in slugs or hermaphroditic humans”. In those cases there is no, or severely limited, competition between sperm. When a couple copulates only the sperm from the other partner is present, it doesn’t need to cpmpete with any other sperm and for this reason there is no need for human males to produce thousands of litres of ejaculate. Nor do male slugs produce litres of sperm. They produce a few mL and no more. If these species were placing as much effort into male function then obviously the weight of sperm at the very least would be equal to the weight of the newborn child or eggs, and yet that isn’t the case.
The reason for that is that under conditions of limited sperm competition male invetment pateaus. After a slug produces a few mL of sperm there is abolutley no benefit at all in producing any more, since that volume will assure maximal fertilisation, and simply increasing volume can’t result in more eggs being fertilised. In contrast more effort put into producing more or larger eggs will result in a more eggs being fertilised or hatching, or in more yong surviving. As a result with species where sperm competition is limited female effort greatly outweigh male effort because there no limit to return on female invesment, while there is a maximal return on male investment.
There are sevaral evolutionary reasons, and although I will describe them they are really only secondary to the ultimate reason.
One is that in hermaphroditic populations organisms won’t ‘knowingly’ mate with an organism they can not impregnate. That makes sense in evolutionary terms since, if I am an hermaphrodite, mating with an already impregnated individual will result in me getting pregnant without imprgenating anyone else. In essence mating with such individuals halves my reproductive success at the very best. Not surprsingly most hermaphrodites have evolved mechanisms that detect when an organismis already impregnated and reject mates based on that.
Another is that reproduction is under hormonal control, and it is fairly dificult to continue to maintain the hormonal control of male reproduction while still maintaining the female balance necessary to produce and carry fertilised eggs. Imagine trying to have fully functional testes while the body is being flooded with progesterone and you will see how hard it gets. Yes it’s is theoretically possible to evolve work-arounds for his problem, but many things are possible but to the best of my knowledge this has never happened.
But in reality the ultimate limiting factor is not evolutionary per se, but just physiological. It requires far more energy to carry fertilised eggs than it does to produce sperm. We can take humans as an extreme example since we are close to monagamous so we are fair comparisons for hemaphrodites, and obviously women put far more energy into every offspring produced than men do. There is an ultimate limit to how much energy any organism can harvest from the environment, and every organism has to ‘decide’ how to apportion that energy. Even if it were prossible to maintain male function while pregnant it still wouldn’t make any sense because the same energetic investment in male function will return far more offspring.
Let’s assume that our species can, in any given year, harvest 100, 000 calories over and above what’s needed to avoid starvation. Let’s also assume that it takes 80, 000 calories for our hypothetical hermaphroditic species to produce one fertile egg and only 20, 000 to produce sufficient sperm to fertilise that egg. That 100, 000 claorie limit is a real limit, it represents the maximum effort possible to allocate to reproductive effort. If our organism remains hermaphroditic obviously it can produce 2 offspring. If it becomes exclusively male it can produce 5 offspring. If it becomes exclusively female it can produce 1.2 offspring. But as you can see there is no excess energy available to the organism that will allow it to continue to to mate even after it is pregnant. The one mating event that results in pregnancy uses up 80, 000 calories to produce the eggs and 20, 000 to impregnate the other partner. There is no energy reserve left to devote to further mating in that season even is pregancy doesn’t interrupt male function. If this individual tries to mate while pregnant it will starve itself to death.
Now obviously the real figures on the amount of excess energy available for reproduction and the relative energetic costs of sperm and egg production cpould be anything at all, but it should be obvious from the above example that so long as male costs are significanty less than female costs then cheating males will be able to produce more offspring than hermaphrodites. That’s because even if being pregnant/gravid doesn’t stall male sexual function any attempt by a pregnant hermaphrodite to produce as many male offspring as an exclusive male will necessarily result that organism starving to death. So long as any one female reproductive event uses more energy than any one male event an organism must have more energy available if it sticks to exclusively male reproduction.
That’s probably because it is a flawed assumption to assume that a gendered species spends (at equilibrium) equal effort on both functions.
Consider a gendered population in which individuals can be male or female. Male individuals in these populations do indeed allocate far fewer resources to male reproduction in many instances, and yet the male:female ratio remains almost even. Many fish and invertebrates for example produce small males that grow to maturity rapidly and invest very little energy in attaining size or in producing sperm. The existence of numerous such species puts paid to your idea that in gendered species invest equal energy in both male and female function. Clearly if all the male effort is undertaken by males that live only a few week and are 1/100th the size of the famles and the male:female ratio is 50% then there can’t possibly be equal effort put into male and female reproduction. The investment in male reproduction is orders of magnitude lower.
I think perhaps that misunderstanding might have been part of Josh’s problem as well. Fischer’s work never implied that any given population will invest as much in male reproduction as female. What it showed was that any population will put as much effort into producing male and female offspring, which is very different. That is to say that no population will produce primarily male offspring even if male offspring grow faster, nor will it produce primarily female offspring even if females have far higher reproductive success.
There is a significant difference between an individual putting equal effort into producing male and female offsrping, and an individual investing equal effort in male and fmeale rpeorductive pathways. You are trying to compare “a hermaprhodite” to “a gendered species”. What you need to do is compare either an hermaphrodite to a a gendered individual or else an hermaphrodiic species to a gendered species. A gendered population in general will produce equal male and female functionaries, but it does that by maintaining an approximately equal sex ratio or individuals. That is very different to an hermaproditic individual placing equal effort into male and female reproduction. And that difference in turn stems from the fact that evoution works on individuals, not populations, while evoutionary effects are seen at the propulation rather than the individual lvel. In essence an hermaphroditic individual has no opportunity to cheat on the sexual invesment, so its investment will be based on simple mathematical return. An hermaphrodite can’t fail to be impreganted and to impregnate at every fertilisation event. As a result any individual maximises it’s chances of reproductive succes by simply allocting resources so that they produces the maximal number of offfspring.
In conditions of total sperm competitions an hermaphrodite will put equal effort into male and female function, it will literally spend as many calorie son producing sperm as in producing ova. It does that because the probability of fertilsing an egg in such conditions in directly proportional to the number of sperm released. Since reproduction by fertilising someone else’s egg is just as good evolutionarly as having one of your own eggs fertilised it pays off to put as mcuh effort into producing sperm as into producing eggs. In other words these individuals in conditions of total asperm competition are maximising there chances of producing zygotes carryimng their gens through both male and female pathways, which means equalinvestment in both pathways.
However once you move away from total sperm competition it is no longer true that the probability of fertilsing an egg in such conditions in directly proportional to the number of sperm released. If an hermaphroditic slug can allocate male:female resources in a 20:80 split and produce 50 fertilised eggs and in turn fertilise 50 eggs then it has produced 100 eggs. If the same slug allocated resources in a 50:50 split then it would only be able to produce 30 fertilised eggs because eggs are more expensive. At the same time it would still only be able to fertile 50 eggs because that is all the eggs the other individual carries and they can be adequately fertiled with only 20% sperm allocation so alloctaing 50% jus results in a lot of wasted sperm. So you can see that simply because each hermaphrodite fertilies and is fertilied there is no scope for cheating. Anything less than mathematically ideal investment only cheats itself, not its partner.
So as you can see neither hermaphroditic nor genedred populations invest equal energy into both reproductive pathways. That is only ever true of hermaphrodites in conditions of total sperm competition.
I apologise for all typos. My spell chacker isn’t working.
