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Another God
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This question isn't as obvious as it first seems. Think about it a bit: Why do we have 2 sexes?
Having 3 sexes doesn't mean u require 3 individuals to participate in reproduction. It just means that sex a can mate with eitehr sex B or sex C. Actually giving each individual more options.Originally posted by FZ+
Because additional sexes will be too complicated, requiring the action of several individuals that is too unreliable and brings too little a benefit.
You don't need sexes for gene swapping and recombination. You can have asexual mating.
Because two sexes allow more capability for adaptation than one.
Originally posted by Another God
Why do we have 2 sexes?
Originally posted by Another God
You don't need sexes for gene swapping and recombination. You can have asexual mating.
It would be twice as efficient (and twice as efficient in evolutionary terms is astronomical) if individuals could mate with anyone, and for every mating event, they literally swapped gametes with each other, getting both of them 'pregnant' (in whatever form that may be).
I don't understand how it is either unproductive or how evolution is harder. What do u mean exactly by asexual mating? I mean any process whereby two diploids form haploid cells internally, then swap those haploids to form new recombined diploids... Exactly the same as sexual reproduction, but without the need to match up in an exclusive pairing system. there isn't even any need for different sexual organs.Originally posted by Innexplicable
Asexual mating is unproductive beacuase adaptation, and evolution is harder
Why is that? Evolution still works as normal. 'Sexual Selection' would also still exist, but it wouldn't be male selecting females or females selecting males, it would be a population wide selection from inside. Only the most attractive individuals get mated with. Same concept, less exclusivity.also the possibility to grow larger is neerly impossible.
Natural Selection takes place with one sex, two sexes, or 42 sexes. Natural Selection even takes places where there is no genetic exchange. I don't get this point either.
Having two sexes allows for natural selection to take place, selecting the best genes, and it also let's us evolve fast in certain situations like in a bottleneck effect. Having 1 sex, carrying both sexual organs (the egg and the sperm) would be illogical, since one most have the best trait of anyone sex. Some species however have the best traits of one sex, and have the other one on standby incase there are a depleted amount of males or females.
Originally posted by Innexplicable
Asexual mating is unproductive beacuase adaptation, and evolution is harder
Originally posted by Another God
The cost of sex is incredibly large if you think about it. In an evolutionary sense, to have two sexes, you need to have two individuals survive to reproductive age, eating x amount of food each etc, just so that one of them can have offspring.
Originally posted by Another God
It would be twice as efficient (and twice as efficient in evolutionary terms is astronomical) if individuals could mate with anyone, and for every mating event, they literally swapped gametes with each other, getting both of them 'pregnant' (in whatever form that may be).
Originally posted by Another God
Each species' biggest threat comes from its own species since they are all competing for exactly the same resources.
Originally posted by Another God First thing to do, is to stop thinking in terms of humans.
Take it back to the begining, back when 'pregnancy' didn't really exist. Think of creatures who form a zygote, and then the zygote grows of its own accord, free from requiring care from the parents.
Plenty of organisms can do this, so an argument claiming that too much effort is required if both organisms are 'pregnant' or both will need to take care of young isn't such a good argument.
So a situation where one species has the ability to have twice as many offspring as a competing species is literally astronomical.
(Each species' biggest threat comes from its own species since they are all competing for exactly the same resources.
So asexual mating already includes meiosis.I don't understand how it is either unproductive or how evolution is harder. What do u mean exactly by asexual mating? I mean any process whereby two diploids form haploid cells internally, then swap those haploids to form new recombined diploids... Exactly the same as sexual reproduction, but without the need to match up in an exclusive pairing system.
I don't understand how it could cost twice as much.Twice as efficient but could cost more than twice as much
There are still species that are hermaphrodite. Best example are snails. How good is there genetics diversity?
Also if you could mate with everyone could that create problem.
I'll say this a few more times, because no one seems to have caught onto it yet: You don't need to have two sexes in order for meiosis => recombination to occur.Originally posted by selfAdjoint
And we need to shuffle to keep up with the bacteria and viruses that infect us in speed of hereitary change.
Things do try to reproduce as much as they can but don't they? It still depends on mating rituals, mate selection (is that other individual good enough for me or not? Will my offspring survive after I invest whatever I invest into them? etc) Every organism does want to have as many offspring as possible, but it also doesn't want to waste its own time/effort/life in doing so.Originally posted by Ambitwistor
Any way you cut it, reproduction has a cost in one way or another; you don't get offspring for free. If you did, everything would reproduce all the time. (Sure, that that kind of growth couldn't be sustained, but so what, if reproducing doesn't cost anything?)
I know that, but being able to produce offspring in times of hardship is advantageous over not being able to. Of course over population could be a problem, but there are other mechanism that ahve evolved to stop that: But this doesn't change the fact that being able to reproduce in harder circumstances, is better than not being able to. That is what evolution works on...the adaptability and ability to continue reproducing no matter how hard the times are...
Having the ability to have more offspring is not necessarily a good thing. Take it to the logical conclusion: why aren't all organisms designed to have thousands of offspring, like insects? It doesn't work well for everybody.
Originally posted by Another God
Things do try to reproduce as much as they can but don't they? It still depends on mating rituals, mate selection (is that other individual good enough for me or not? Will my offspring survive after I invest whatever I invest into them? etc) Every organism does want to have as many offspring as possible, but it also doesn't want to waste its own time/effort/life in doing so.
I know that, but being able to produce offspring in times of hardship is advantageous over not being able to.
How often have you heard the saying "I wouldn't have sex with you if you were the last man on earth"? Well, what if there was one man left on earth? How would the race continue to reproduce?
Originally posted by Another God
Hermaphrodites change from male to female right?
Originally posted by Another God
Each species' biggest threat comes from its own species since they are all competing for exactly the same resources.
Originally posted by Monique
The reason that microorganisms don't need meiosis (in my opinion) is that they divide very very fast and are able to adapt to their environment much quicker than mammals do. They can take up genes from their environment and loose genes when they don't need them.
Originally posted by Another God
Have you ever wondered why the Y chromosome is so much smaller than the X chromosome?
I think this is a good point...its got me thinking...Originally posted by Ambitwistor
Isn't that my point? Organisms don't actually reproduce as much as possible, because there are costs involved in doing so. In fact, it may be advantageous to have half the population incur different costs than the other half.
But even if he could reproduce asexually as well as sexually, I wouldn't give good odds of the race surviving anyway, if conditions were so harsh that it was already narrowed down to one remaining organism, especially when all you're doing is perpetually producing genetically identical copies (other than the occasional mutation) of that one organism
In other words, I am not talking about self fertilisation, or about budding, or cloning. I am talking about sexual redproduction, without needing two exclusive sexes.I'll say this a few more times, because no one seems to have caught onto it yet: You don't need to have two sexes in order for meiosis => recombination to occur.
Sexual reproduction can be done without need of two exclusive sexes. Why are 2 sexes so predominant?
I am not talking about hermaphrodites, I am talking about there being no sexes. There would still be sexual reproduction.Originally posted by iansmith
Genetic diversity becomes important. If your genetic diversity as a species does not increase due to hermaphrodites, then what is the point of having numerous individuals becoming pregnant.
Competition from within doesn't count against the species in terms of evolution though. If internal competition is the worst competition, then the species is doing great evolutionarily. Think about it...I'm sure you know what i mean.
So limiting the number of individuals that becomes pregnant, limits the number of new individuals and it limits the competition.
I can imagine a complex version, but I am sure you can imagine the same simple version that I am thinking of. Some organisms exist in which there are many sexes. They don't require all of the sexes to be involved, what they require is one from a sex other than themselves.Why 2? 3 is too many. Can you imagine the complexity of 3 different kind of sex.
No i haven't. But you left out Insects. They also have a xsome dependenve for sex. They do it differently (ie: no Y at all), but they still do it.Originally posted by iansmith
Have you ever wonder why only mamals have this chromosome dependent sex determination?
As for the last male on Earth scenario, I never said the species was on the brink of extinction, I said there was only one male...which of course, in the situation of any 2 sex species would put it on the brink of extinction.
Secondly, the scenario doesn't even have to apply to worldwide, extinction event ideas. Populations can get separated at any time, and if that population happens to have incredibly few females, then the species is put into immediate risk.
please read the other posts aswell:
In other words, I am not talking about self fertilisation, or about budding, or cloning. I am talking about sexual redproduction, without needing two exclusive sexes.
Nature. 2002 Dec 12;420(6916):664-6. Related Articles, Links
Sex releases the speed limit on evolution.
Colegrave N.
Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh EH9 3JT, UK. n.colegrave@ed.ac.uk
Explaining the evolutionary maintenance of sex remains a key problem in evolutionary biology. One potential benefit of sex is that it may allow a more rapid adaptive response when environmental conditions change, by increasing the efficiency with which selection can fix beneficial mutations. Here I show that sex can increase the rate of adaptation in the facultatively sexual single-celled chlorophyte Chlamydomonas reinhardtii, but that the benefits of sex depend crucially on the size of the population that is adapting: sex has a marked effect in large populations but little effect in small populations. Several mechanisms have been proposed to explain the benefits of sex in a novel environment, including stochastic effects in small populations, clonal interference and epistasis between beneficial alleles. These results indicate that clonal interference is important in this system.
Science. 1998 Sep 25;281(5385):2003-8. Related Articles, Links
Sex and conflict.
Partridge L, Hurst LD.
Galton Laboratory, Department of Biology, University College London, London NW1 2HE, UK.
Evolutionary conflict occurs when the deterministic spread of an allele lowers the fitness either of its bearer or of other individuals in the population, leading to selection for suppressors. Sex promotes conflict because associations between alleles are temporary. Differing selection on males and females, sexual selection, and differences in transmission patterns between classes of nuclear and cytoplasmic genes can all give rise to conflict. Inert Y chromosomes, uniparental inheritance of cytoplasmic genes, mating strains and sexes, and many features of sexual behavior may have evolved in part as a result of evolutionary conflict. Estimates of its quantitative importance, however, are still needed.
Originally posted by Another God
I suppose it has to do with being Diploid for starters. Can u give me an example of a Diploid species which doesn't have a xsome dependence?
Originally posted by Monique
Plants don't, plants are sex-dependent or hermaphrodite.
Originally posted by Monique
I am still interested to find out what the reproductive cells of lower organisms look like, are they all so specialized as sperm and egg cells? Or are there organisms where they essentially look the same?
We use all of our brain.Originally posted by StarkyDee
using more than 10% of our brain
The existence of only 2 sexes in nature is due to a combination of evolutionary and genetic factors. In most species, sexual reproduction is the primary means of reproduction, and having 2 distinct sexes allows for genetic diversity and the passing on of beneficial traits to offspring. Additionally, having 2 sexes also helps to prevent inbreeding and maintain a healthy population.
Yes, there are some species that do not conform to the traditional 2 sex system. For example, some species of plants and fungi have multiple sexes, while some species of fish and reptiles can change their sex throughout their lifetime. However, these exceptions are relatively rare and do not change the fact that 2 sexes are the most common in nature.
The division of sexes into male and female is largely based on the presence of different sex chromosomes. In most species, males have one X and one Y chromosome, while females have two X chromosomes. This genetic difference leads to the development of different reproductive organs and hormones, resulting in the physical differences between males and females.
Intersex individuals, who possess both male and female reproductive organs, are a result of genetic and developmental variations. This can occur due to genetic mutations or hormonal imbalances during fetal development. Intersex individuals are relatively rare and do not challenge the existence of 2 sexes in nature.
It is possible that there could be more than 2 sexes in nature, as seen in some species. However, the 2 sex system has been successful in promoting genetic diversity and maintaining healthy populations, so it is unlikely that it will change significantly in the future. Additionally, the division into 2 sexes is deeply ingrained in the genetics and biology of most species, making it difficult for a significant shift to occur.