Originally posted by PenguinSexual reproduction does not require male and female. In fact there are plenty of examples of sexual reproduction without male and female present.
However sexual reproduction requires 2 separate & different cells - a sperm & an egg, which combine their genetic material. It's not immediately clear to me how this system can have evolved from, presumably, a single cell just multiplying.
The separation into sexes has evolved more than once with differing results. For example some species have the female having two identical Chromosomes(XX) and the Male with a unique one (XY)
Others work the other way round with the female having different chromosomes.
I believe that there are species with apparent male and female which actually have identical genes and environmental factors determine sex. (some trees for example).
Note also that most plants have male and female organs on one plant.
Clearly, the organism would not have split into male & female until long after the separate egg & sperm evolved. Fertilisation would have happened within the individual initially but how did it first come about?
Sexual reproduction takes place in most 'higher' life forms including single celled organisms, plants and animals. To discuss the evolution of eggs and sperms is to imply sexual reproduction is unique to animals. The differences between sexes can take place gene by gene, all it takes is one chromosome to be slightly shorter than another and then the genes on the leftover piece are always transfered as a group enabling the evolution of a species within a species (male and female).
How it taking 1/2 the genetic material from one of my own cells and 1/2 form another beneficial? Surely the material is the same?
The benefit of sexual reproduction is enormous as it allows the mixing of genes. This enables one beneficial trait to join with another beneficial trait thus greatly enhancing the power of evolution. It must be noted that it is not the only mechanism for gene mixing and there are even interspecies mechanisms taking place.
Sexual reproduction does not require male and female. In fact there are plenty of examples of sexual reproduction without male and female present.
Ok fair enough. I realise that 'male' and 'female' are not neccessary, that plants are both for example. All it needs is for the offspring to take its genes from more than one parent (or separate cells of the same parent). But if you are taking your genetic material from different cells of the same organism, those cells will have the same genetic material within them: all the cells in the body have the same genes so where's the advantage? If a plant fertilises itself isn't that the same as a clone?
The separation into sexes has evolved more than once with differing results. For example some species have the female having two identical Chromosomes(XX) and the Male with a unique one (XY)
Others work the other way round with the female having different chromosomes.
I didn't know this, thanks.
Sexual reproduction takes place in most 'higher' life forms including single celled organisms, plants and animals. To discuss the evolution of eggs and sperms is to imply sexual reproduction is unique to animals.
I thought it might cause problems saying 'egg' and 'sperm' when I wrote it but I can't remember the more generic term.
The differences between sexes can take place gene by gene, all it takes is one chromosome to be slightly shorter than another and then the genes on the leftover piece are always transfered as a group enabling the evolution of a species within a species (male and female).
This I'd like to know more about. I think it might be part of the answer I'm looking for but I don't really understand what you are saying! I think you are describing how sexual reproduction can result in two separate sexes but I'm looking for how the sexual reproduction evolved in the first place.
The benefit of sexual reproduction is enormous as it allows the mixing of genes. This enables one beneficial trait to join with another beneficial trait thus greatly enhancing the power of evolution. It must be noted that it is not the only mechanism for gene mixing and there are even interspecies mechanisms taking place.
I know the benefit of sexual over asexual reproduction is vast, but to take an example, I can see how flight came about: a variation on a feature happens to behave very slightly like an aerofoil, giving its owner a tiny advantage when leaping. Over hundreds / thousands of generations those with more winglike features tended to survive better than those with less winglike features and so wings evolved.
Going back to reproduction, on the one hand you have organisms that simply replicates themselves with the occasional error (asexual) and on the other you have organisms that replicate by combining some of one individuals genetic material with some from another individual. This is not a mechanism that can have evolved in one step, that's not how evolution works. I can see how a 'proto wing' would be an advantage but what was 'proto sexual reproduction' and how did it provide an advantage?
I feel like I'm thinking like a creationist here and failing to see what the sexual reproduction equivalent of '1/2 a wing' or '1/2 an eye' is.
--- Penguin.
Originally posted by PenguinSexual reproduction evolved as a supplement to asexual reproduction. When the conditions around the organism are changing rapidly, it uses sexual reproduction to combine all the most survival promoting genes into a really tough breed which can survive any dangers that may come. However, they switch to asexual reproduction at times which are more constant, as the organism that's around clearly lives well under those conditions. As sexual reproduction evolved, it eventually became more and more effective and the asexual reproduction genes eventually became a hinderance.
[b]Sexual reproduction does not require male and female. In fact there are plenty of examples of sexual reproduction without male and female present.
Ok fair enough. I realise that 'male' and 'female' are not neccessary, that plants are both for example. All it needs is for the offspring to take its genes from more than one parent (or separate cells o ction equivalent of '1/2 a wing' or '1/2 an eye' is.
--- Penguin.[/b]
http://www.redhotpawn.com/board/showthread.php?threadid=42246&page=2
I will speculate however. There are two events that take place in sex; meiosis and fusion. These are two opposite events; one cell splits to produce two "half cells" and two "half cells" fuse to form one new cell. They seem to be in fact the same event, but which can go in either direction. I think that the first organisms were haploid, and a fusion event is what led to an asexually reproducing diploid organism. Such fusion events would provide the benefits of sexual reproduction in terms of masking deleterious genes and combining advantageous ones, but could not continue indefinitely as the chromosome number doubles each time fusion occurs. The new diploid cell could then mutate in such a way as to reverse the fusion procedure; maybe no new mutation would be even needed. In chemistry, we learn of a concept called "reversible reactions" in which reactions can occur in both directions. In fact all reactions are reversible, but there is often a bias for one "side" of the reaction. The fusion event would have been reversible from the beginning by this principle, though how often it would reverse is not defined by the existence of reversibility. Thus with the evolution of fusion you also simultaneously evolve "anti-fusion" or meiosis.
http://www.redhotpawn.com/board/showthread.php?threadid=42246&page=4
Originally posted by PenguinNo, it is not. Each of your cells contains two possible genes at each point in a chromosome of which only one is expressed. Sexual reproduction with yourself (lets assume you are a tree) results in some of the unexpressed (recessive) genes getting doubled up and therefore expressed. This can be beneficial, but is not nearly as good as sexual reproduction with another organism. This is the same reason why incest is discouraged.
If a plant fertilises itself isn't that the same as a clone?
Originally posted by twhiteheadOf course, thanks for reminding me. I have clearly forgotten huge swathes of the biology I learnt at school.
No, it is not. Each of your cells contains two possible genes at each point in a chromosome of which only one is expressed. Sexual reproduction with yourself (lets assume you are a tree) results in some of the unexpressed (recessive) genes getting doubled up and therefore expressed. This can be beneficial, but is not nearly as good as sexual reproduction with another organism. This is the same reason why incest is discouraged.
--- Penguin.
Originally posted by PenguinYou may be interested in Matt Ridley's book "The Red Queen Hypothesis" which, to my mind, provides the best explanation for the evolution of sex.
I'd be interested in sexual reproduction, no not like that but in the way it evolved! I've heard lots of creationist arguments about the eye & various other organs being too complex or only useful in their current form, all of which is clearly rubbish and explained many times in this thread.
However sexual reproduction requires 2 separate & different cel ...[text shortened]... /2 form another beneficial? Surely the material is the same?
I'm rambling.
--- Penguin
Just the fact that the "debate" concerning Random Selection v Creation won't go away says a lot IMHO.
The best scientific argument seems to be .. " If you disagree it's because you're to stupid to understand", while the best Creationist argument seems to be ... faith.
Take your pick.
IMO neither argument is conclusive and the issue is still unexplained.
Originally posted by jammerThe best scientific argument seems to be .. " If you disagree it's because you're to stupid to understand"
Just the fact that the "debate" concerning Random Selection v Creation won't go away says a lot IMHO.
The best scientific argument seems to be .. " If you disagree it's because you're to stupid to understand", while the best Creationist argument seems to be ... faith.
Take your pick.
IMO neither argument is conclusive and the issue is still unexplained.
The scientific response to most creationist arguments is "no, that's not how it works". Many creationist arguments are based on fundamental misconceptions about the process. Most of the remainder are based on logical or statistical fallacies.
The fact that you called it Random Selection indicates that there may be one of the most common misconceptions happening again here. Natural Selection is not random, as has been explained many times in this thread.
IMO neither argument is conclusive and the issue is still unexplained.
It's about as conclusive as any other scientific theory in existence.
--- Penguin.
Originally posted by scottishinnzI assume you meant The Red Queen rather than The Red Queen Hypothesis. Thanks for the recommendation, it looks interesting and I've added it to my wish list.
You may be interested in Matt Ridley's book "The Red Queen Hypothesis" which, to my mind, provides the best explanation for the evolution of sex.
--- Penguin.
Originally posted by jammerActually, generally, the scientific argument is "You are generally clever enough to understand, but you are either deliberately misrepresenting it, have had it misrepresented to you, or don't fully understand statistics and probability".
Just the fact that the "debate" concerning Random Selection v Creation won't go away says a lot IMHO.
The best scientific argument seems to be .. " If you disagree it's because you're to stupid to understand", while the best Creationist argument seems to be ... faith.
Take your pick.
IMO neither argument is conclusive and the issue is still unexplained.
Originally posted by jammerIt says a lot about the power of faith. It doesn't say much about the validity of either argument.
Just the fact that the "debate" concerning Random Selection v Creation won't go away says a lot IMHO.
The best scientific argument seems to be .. " If you disagree it's because you're to stupid to understand", while the best Creationist argument seems to be ... faith.
If that was our argument (scientists) then this thread would not exist. This thread is about answering any questions/queries etc and helping anyone who is interested to understand. Nearly anyone who is sufficiently interested in the subject should be able to understand most of the basics of evolution. To successfully put up a scientific counter argument they should infact be able to understand it quite thoroughly or they are merely claiming "I dont understand it therefore its wrong" or "I know its wrong for reasons which do not require and understanding". However that would probably not be scientific reasons.
Take your pick.
IMO neither argument is conclusive and the issue is still unexplained.
Well that depends on what you mean by "conclusive" or by "unexplained". The theory of evolution is as conclusive as the theory of gravity.