The egg came before the chicken. The chicken's ancestors were laying eggs far before anything you'd recognize as a chicken or even a bird or reptile came to be. Fish lay eggs. In fact, eggs exist for any sexually reproducing organism; they just have variations between species.
Can the intermediate stages, even over millions of years, be postulated from a non-egg laying reproductive system to an egg-laying reproductive system?
Absolutely. There are organisms which do both. Sexual 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.
According to the principles of speciation, neither the chicken nor the egg came first
This is incorrect.
Originally posted by scottishinnzDon't bother. CalJust appears from time to time with "honest questions." When a biologist or other natural scientist takes the time to answer his questions, he does the typical torturous song and dance routine. After a month or so of this even he will tire of his charade and disappear.
CJ, it seems the only answer that would placate you would be "we don't know". Unfortunately for you, we do.
All higher animals have eggs, mammals included. The only differences between a bird egg and a mammal egg are size and calcification. Calcification could easily have progressively evolved as animal made their first transition from an aquatic ...[text shortened]... over time, in the same way that ancestral aurochs were smaller than modern cows.
So now he's back with the same "honest questions." This one is a complete waste of time.
Originally posted by telerionI concur: it will prove to be a complete waste of time, as is the same for the remaining posts on this site. Never is anything resolved.
Don't bother. CalJust appears from time to time with "honest questions." When a biologist or other natural scientist takes the time to answer his questions, he does the typical torturous song and dance routine. After a month or so of this even he will tire of his charade and disappear.
So now he's back with the same "honest questions." This one is a complete waste of time.
Because you're only seeing a snapshot of whats happening, perhaps in your entire lifetime you'd see 1 ten thousandth of one percent of the time required to make that full change from a soft amphibious egg to a hard-shelled reptile egg. You simply can't see something happening on this time scale. It's like trying to watch a tree growing in real time - pointless - but that doesn't mean trees don't grow!
Sorry, you won't get away that easily!
I don't care about lengths of time, take the millions of years that you want to! However, if I saw a tree in year x, and came back after a zillion years and saw that the tree is now a house, I would like to know what the interim stages where at, say, a zillion/100, or a zillion/10, or a zillion/2. It does not concern me that you cannot NOTICE or MEASURE a change over a human lifetime, that's besides the point. What concerns me is what the interim stages were (or could possibly have been theoretically) that were reached by incremental "copying errors" that gave the organism the edge on survival.
Your "soft mammalian egg" to hard bird egg explanation is also extremely unsatisfactory. If the soft egg changed incrementally to a "sort-of" or "almost" hard egg, that would have been a disadvantage, not an advantage!! It would not have propagated.
The whole point about bisexual progeneration to have evolved from unisexual, or asexual, reproduction is also an impossible matter to explain. That would require similar, and complementary, beneficial mutations to occur in separate groups of animals where some animals developed male organs, and others female organs, and only when both where fully formed, over many, many, thousands of generations, then suddenly they could reproduce bisexually!
The only argument you have is that: this is what we have now, so it MUST have happened. Nobody is prepared to suggets HOW! I am suggesting it cannot have!
In peace
CJ
Your "soft mammalian egg" to hard bird egg explanation is also extremely unsatisfactory. If the soft egg changed incrementally to a "sort-of" or "almost" hard egg, that would have been a disadvantage, not an advantage!! It would not have propagated.
Specifically why would a harder shell have been more of a disadvantage than a softer shell?
The whole point about bisexual progeneration to have evolved from unisexual, or asexual, reproduction is also an impossible matter to explain. That would require similar, and complementary, beneficial mutations to occur in separate groups of animals where some animals developed male organs, and others female organs, and only when both where fully formed, over many, many, thousands of generations, then suddenly they could reproduce bisexually!
This is a lesson on why you shouldn't use such absolute terminology as "impossible" and "would require" as if you have analysed all the possibilities. You haven't. Your explaination above precludes the possibility of an asexual organism possessing and using both fully working male and female organs as many assexually reproducing plants do.
Originally posted by CalJustNice one.
[i]Because you're only seeing a snapshot of whats happening, perhaps in your entire lifetime you'd see 1 ten thousandth of one percent of the time required to make that full change from a soft amphibious egg to a hard-shelled reptile egg. You simply can't see something happening on this time scale. It's like trying to watch a tree growing in real time - poin ...[text shortened]... y is prepared to suggets HOW! I am suggesting it cannot have!
In peace
CJ
Finally some extremely well thought out questions about evolution.
I should say that I don't have any answers to your questions, although I would guess that there are some out there somewhere. You're right about simply saying 'this is what we have now so it must have happened somehow' is not satisfactory. We want to understand. It's the human drive.
On the egg side of things, I would guess that the transition from soft to hard shell occurred somewhere in the transition from sea to land animals. Sea creatures tend to have soft eggs, where reptiles don't. Soft eggs are fine for ocean habitats - or for many of them anyway. I can imagine a transition occurring as animals made tentative forays into a semi-aquatic life.
The transition back to soft eggs for mammals (or most mammals - don't forget the monotremes - platypus and echidna - still lay hard eggs) would've come much later, I'm guessing.
As for sex.
I don't have an answer to that one.
But I would think there are some hypotheses.
I'll have a look around and see what I can find.
Originally posted by CalJustsuggest something that covers all the evidence,instead of denying that it exist.
Because you're only seeing a snapshot of whats happening, perhaps in your entire lifetime you'd see 1 ten thousandth of one percent of the time required to make that full change from a soft amphibious egg to a hard-shelled reptile egg. You simply can't see something happening on this time scale. It's like trying to watch a tree growing in real time - poin y is prepared to suggets HOW! I am suggesting it cannot have!
In peace
CJ
BTW I have shown enough of the evidence in other posts and I don't feel like repeating it.
Suffice to say, the religicos put so much pressure on scientist that the scientist adopted radiation as the most likely cause of change in natural selection, thereby tossing out LaMarch and not seeing the epigenetical factors until quite recently.
The whole point about bisexual progeneration to have evolved from unisexual, or asexual, reproduction is also an impossible matter to explain. That would require similar, and complementary, beneficial mutations to occur in separate groups of animals where some animals developed male organs, and others female organs, and only when both where fully formed, over many, many, thousands of generations, ...[text shortened]... e happened. Nobody is prepared to suggets HOW! I am suggesting it cannot have!Your "soft mammalian egg" to hard bird egg explanation is also extremely unsatisfactory.
In peace
CJ[/b]
I am not sure what this explanation was, but mammalian eggs and bird eggs both came from reptile eggs; not bird eggs from mammalian eggs.
If the soft egg changed incrementally to a "sort-of" or "almost" hard egg, that would have been a disadvantage, not an advantage!!
Not true. Reptile eggs would be this "sort of" hard egg with their flexible but thick and leathery protective shell. It allows them to lay eggs on land, which amphibians cannot do.
That would require similar, and complementary, beneficial mutations to occur in separate groups of animals where some animals developed male organs, and others female organs, and only when both where fully formed, over many, many, thousands of generations, then suddenly they could reproduce bisexually!
No. There's no reason you need male and female for sexual reproduction. Sexual reproduction involves meiosis followed by cell fusion. The products of meiosis do not have to be well differentiated "eggs" and "sperm"; the two cells which fuse could be identical except for the genes they carry. I haven't done a lot of research about the evolution of sex, so I may be uninformed about what people have been discovering though.
Here's what talkorigins says:
1. The variety of life cycles is very great. It is not simply a matter of being sexual or asexual. There are many intermediate stages. A gradual origin, with each step favored by natural selection, is possible (Kondrashov 1997). The earliest steps involve single-celled organisms exchanging genetic information; they need not be distinct sexes. Males and females most emphatically would not evolve independently. Sex, by definition, depends on both male and female acting together. As sex evolved, there would have been some incompatibilities causing sterility (just as there are today), but these would affect individuals, not whole populations, and the genes that cause such incompatibility would rapidly be selected against.
2. Many hypotheses have been proposed for the evolutionary advantage of sex (Barton and Charlesworth 1998). There is good experimental support for some of these, including resistance to deleterious mutation load (Davies et al. 1999) and more rapid adaptation in a rapidly changing environment, especially to acquire resistance to parasites (Sá Martins 2000).
http://www.talkorigins.org/indexcc/CB/CB350.html
Here's another relevant site:
http://biomed.brown.edu/Courses/BIO48/19.Evol.of.Sex.HTML
Originally posted by CalJustStop mis-quoting me. Go back and re-read the post (or actually just READ it).
[i]
Your "soft mammalian egg" to hard bird egg explanation is also extremely unsatisfactory. If the soft egg changed incrementally to a "sort-of" or "almost" hard egg, that would have been a disadvantage, not an advantage!! It would not have propagated.
The whole point about bisexual progeneration to have evolved from unisexual, or asexual, reproduction ...[text shortened]... ened. Nobody is prepared to suggets HOW! I am suggesting it cannot have!
In peace
CJ
The transition would have been fish -> amphibian -> reptile ->Birds
reptile->Mammals
Fish have soft eggs and need to lay them in water.
At some point amphibians evolved the ability to live predominantly on land, but still had to return to water to reproduce. Eggs that are more able to resist desication would have been of benefit, because they could be layed further away from the water, and hence further away from predators.
At some point reptiles evolved. Reptile reproduction is fully independant of free water. The egg is a sealed unit. (some exhibit vivipary)
Birds also have a similar system.
Mammals exhibit a reduced system. They simply do not expel their eggs, hence without any need for the calcification of shells, which would have an evolutionary cost, since the parent would not suffer reduced mobility.
Originally posted by CalJustHow would you know whether they are intellectually satisfying? You show no sign of being an intellectual.
Lots of answers, none of which are in any way satisfying intellectually.
Please give a more detail of what you want examples of. Do you want an example of a non-chicken developing into a chicken or a non-bird developing into a bird or what? Egg laying is general term maybe you should give a precise definition of what you are talking about.
Sexual reproduction does not mean distinct male and female organisms. Plants for example are normally bisexual and so are some animals.
Telerion
Sure, when you have no answers, everything is a “waste of time”.
By the way, contrary to your accusation, I have never before posed an “honest question”. In previous debates (which turned out just as pointless) I always took a strong pro-creation point of view. However, since I have had a separate debate with an evolutionist friend of mine, who could not answer this question, I tried the RHP experts. Sadly, no answer here either, merely abuse.
A1000Y
There's no reason you need male and female for sexual reproduction. Sexual reproduction involves meiosis followed by cell fusion. The products of meiosis do not have to be well differentiated "eggs" and "sperm"; the two cells which fuse could be identical except for the genes they carry.
So are you suggesting that at some point the chicken carried both “eggs” and “sperm” together in one animal, and then later in half the population the “eggs” stopped gradually and the “sperm” took over, and in the other part of the population the reverse occurred??
Scottishinnz
Stop mis-quoting me. Go back and re-read the post (or actually just READ it). The transition would have been fish -> amphibian -> reptile ->Birds
Actually, YOU should re-read my original question. I never mentioned the evolution of birds, merely the egg-laying phenomena. Other posters put in the bird issue. In your model, one would have to ask the question: when did whatever Fish came from, first start laying eggs? And what were the intermediary steps from this non-egg-laying creature to the egg-laying creature?
Twithead
Off course, YOU are the intellectual!
Please give a more detail of what you want examples of. Do you want an example of a non-chicken developing into a chicken or a non-bird developing into a bird or what? Egg laying is general term maybe you should give a precise definition of what you are talking about.
Sorry, I really don’t know how to say it more explicitly, but if you don’t understand it, you can always pass.
The problem for me (and it really IS an honest problem) is that I cannot visualize a process whereby a non-egg-laying organism, that reproduces by itself (as they must all have done at the beginning) can, in tiny stages that are each incrementally beneficial for survival when compared with the previous stage, develop into an egg-laying mechanism. That applies to chickens, birds, fish, reptiles etc. As the saying goes, there is no such thing as being “half pregnant”.
The closest explanation has come from A1000Y:
The variety of life cycles is very great. It is not simply a matter of being sexual or asexual. There are many intermediate stages. A gradual origin, with each step favored by natural selection, is possible (Kondrashov 1997). The earliest steps involve single-celled organisms exchanging genetic information; they need not be distinct sexes. Males and females most emphatically would not evolve independently. Sex, by definition, depends on both male and female acting together. As sex evolved, there would have been some incompatibilities causing sterility (just as there are today), but these would affect individuals, not whole populations, and the genes that cause such incompatibility would rapidly be selected against.
I will look up Kodrashov 1997. However, the rest of this quote also just assumes that “as sex evolved” but does not postulate any intermediate stages.
Many hypotheses have been proposed for the evolutionary advantage of sex (Barton and Charlesworth 1998). There is good experimental support for some of these, including resistance to deleterious mutation load (Davies et al. 1999) and more rapid adaptation in a rapidly changing environment, especially to acquire resistance to parasites (Sá Martins 2000).
I am sure one could find excellent proof of the benefits of sex (not to mention the fun of it) but that would, at best, provide the motivation for, not the methodology of, its evolution.
Maybe it’s time for me to disappear again for a year or two….
CJ
Originally posted by CalJustAll animals have eggs. This is where your problem is. Fish, amphibians, reptiles all lay external eggs. Birds also lay eggs. Mammals have internal eggs, with exception of the ducked-billed playtupus (sp?): natural's joke.
Can somebody please help me here?
As I understand it, evolution is based on the following two principles:
1 During reproduction, small "copying errors" occur, call them mutations.
2 Natural selection then works on these copying errors, and beneficial ones are preferentially selected for continuation. The sum of many such beneficial mutations, over ...[text shortened]... ying.
This is an honest request. Can somebody please help me here?
In peace
Cal Just