07 Aug 11
1 edit
Originally posted by CalJust[/b]Your problem is a lack of imagination, really. Large features like eyes, pouches, wombs etc. don't evolve with a single mutation but it takes a long time. You can't have "half a knee" either, but is it really so hard to imagine how knees might have evolved?
Hi twhitehead, welcome back,
You said that I refer to a whole host of problems - let us focus on only one. I am taking this as a personal challenge to try to get understood, because I am still convinced that you are not actually understanding the point I am trying to make.
I said: [b]What could possibly have been any one of the many intermediate stages
If you don't see the problem this time around, I will throw in the towel and give up!
07 Aug 11
Originally posted by KazetNagorraYou are stating the obvious.
Large features like eyes, pouches, wombs etc. don't evolve with a single mutation but it takes a long time. You can't have "half a knee" either, but is it really so hard to imagine how knees might have evolved?
We are here not talking about the evolution of SPECIES or FEATURES, but of reproductive systems
07 Aug 11
Originally posted by KazetNagorraReproduction implies a complex intelligent mechanism.
The first sexually reproducing organisms most likely had very simple forms of sexual reproduction. More complex forms then evolved from the more basic forms of sexual reproduction.
Cheating science denies intelligence as a factor required for evolution.
Cheating science presents that matter without intelligent direction makes way for reproduction.
This is clearly absurd.
07 Aug 11
Originally posted by DasaAnd using drugs is cheating one's brain, sort of.
Reproduction implies a complex intelligent mechanism.
Cheating science denies intelligence as a factor required for evolution.
Cheating science presents that matter without intelligent direction makes way for reproduction.
This is clearly absurd.
07 Aug 11
Originally posted by KazetNagorraAt the cellular level, non-sexual reproduction is the norm in all life as far as I am aware. Only in complicated multicelular life forms does sexual reproduction become a necessity and even then, sexual reproduction between two individuals is only a necessity where sexual differentiation has taken place (think of plants where self fertilization is common place), and even then there are cases of females reproducing on their own (I have heard of some reptiles being capable of this).
Presumably sexual reproduction evolved from non-sexually reproducing lifeforms. A possible mechanism for this is for the possibility of sexual reproduction to arise alongside non-sexual reproduction. At first there would be only very small differences between the sexes, but after some time one could imagine the possibility for non-sexual reproduction to disappear and the differences between the sexes to enlarge.
Sexual reproduction allows much faster evolution because it mixes up the genes. This is true even for self fertilization.
07 Aug 11
2 edits
Originally posted by CalJustTo be honest, I haven't studied this particular case in detail, and a brief scan of Wikipedia suggests that it is not known for sure whether mammals descended from a Marsupial like ancestor. But if one was to imagine an intermediate stage between an egg laying animal (like the platypus) and a mammal, then the marsupial fits quite nicely. The challenge was to immagine an immediate stage.
It is true that marsupials can be imagined to be an "intermediate" stage between current mammals and some pre-mammalian stage.
Furthermore, the ongoing process of evolution my see them change into something else, hence they can be seen as "intermediary", I agree. But each baby marsupial has a mommy and daddy, and produces marsupial off-spring.
At this point, no, they are not evolving into mammals, and are intermediaries between their ancestors and their descendants. But it remains the case that the ancestor of mammals could have had features that today would cause us to classify it as a marsupial.
You agree, of course, that there must have been a first one? If NOT, then this is the place to stop this discussion.
I think you may have a problem with gray areas here. What constitutes a pouch? A fold of skin 1 inch wide? A fold of skin 2 inches wide? Exactly how many inches must the skin fold before it is a pouch? If the family line adds on average 1/1000th of an inch per generation, then can you spot the generation in which the first pouch born child was born?
If you do NOT believe that there was a first marsupial, do you say that there was a partial one, i.e. with only half a pouch?
I do not believe all marsupials have pouches.
If you don't see the problem this time around, I will throw in the towel and give up!
I see the problem is that you cant think of any intermediary stages in some instances. And maybe neither can I. But it remains the case that the most reasonable explanation at this point is that there was an intermediary stage and whether we can ever find out what that stage was remains to be seen.
But my advice for anyone wanting to imagine intermediary stages is to start by studying some of the strange and wonderful variety of life that is out there, and you may find that what you think is impossible is actually quite common.
I might point out here that some snakes give birth to live young and some lay eggs. The evolution of live birth from egg laying is not unique to mammals, it has happened many times with many groups of animals. (I can think of frogs, fish and sharks off hand).
I read somewhere that some ghekos lay eggs or have live birth depending on the circumstances. That makes a mess of your 'sudden transition' game.
08 Aug 11
Originally posted by twhitehead. What constitutes a pouch? A fold of skin 1 inch wide? A fold of skin 2 inches wide? Exactly how many inches must the skin fold before it is a pouch?
This is what both you and everybody else that has responded to me confuses constantly: The difference between the evolution of FEATURES(like a pouch) and a SYSTEM (like a baby being placed in it.)
Obviously, as I have said many times, I accept that Features like pouches etc can develop by small increments over time. However, a SYSTEM like having a baby in a pouch cannot develop gradually: either it is IN the pouch (of whatever size!) or it is NOT!
An even more difficult SYSTEM to have developed gradually, is the egg-larva-pupae-moth system. (And to say that there are many similar but different systems that can be arranged to appear as a progression, again misses the point. Because all these are fully developed and functional SYSTEMS in their own right, and my argument would apply fully to them also.)
I read somewhere that some ghekos lay eggs or have live birth depending on the circumstances. That makes a mess of your 'sudden transition' game.
Ths is the closest that we have come to an answer. I believe that it could be possible that two parallel systems develop of which one would gain the dominance over time.
CJ signing out of this discussion. It's been a fun ride.
08 Aug 11
Originally posted by CalJustIf there is confusion then you are partly responsible for it. I replied to your post:
This is what both you and everybody else that has responded to me confuses constantly: The difference between the evolution of FEATURES(like a pouch) and a SYSTEM (like a baby being placed in it.)
Now let us take the very first primordial marsupial, the guy (or gal) that first developed a pouch to place an underdeveloped fetus in.
How did THAT particular marsupial get born? Did it grow up in a pouch? No, of course not, because by definition I postulated that it was the first one!
Which clearly shows that you don't realise that the development of a pouch could be gradual.
Obviously, as I have said many times, I accept that Features like pouches etc can develop by small increments over time. However, a SYSTEM like having a baby in a pouch cannot develop gradually: either it is IN the pouch (of whatever size!) or it is NOT!
Now you are not making any sense. If the pouch can develop gradually, then a system that includes a pouch is necessarily also developing gradually, and could develop from a system with no pouch to one with a pouch. As I already stated, I don't think all marsupials have pouches which essentially proves that it is not a required part of the system.
An even more difficult SYSTEM to have developed gradually, is the egg-larva-pupae-moth system. (And to say that there are many similar but different systems that can be arranged to appear as a progression, again misses the point. Because all these are fully developed and functional SYSTEMS in their own right, and my argument would apply fully to them also.)
Why do you keep jumping from one example to another? First it was sexual reproduction, then pouches, now insects. Its as if you don't actually want an answer, you just want to hold onto your belief that at least one question can't be answered.
08 Aug 11
2 edits
Originally posted by twhiteheadAs I already stated, I don't think all marsupials have pouches which essentially proves that it is not a required part of the system.
Why do you keep jumping from one example to another? First it was sexual reproduction, then pouches, now insects.
The reason why I keep jumping from one example to another, is because it is not any ONE system which intrigues me (insects, marsupials, what-have-you) but the concept that at least superficially, ANY reprodutive system can only reproduce in the way that itself was reproduced. So where do they all come from?
That is also why the discussion about how a pouch got formed, or the fact that some marsupials have no pouches, is a red herring.
Actually, I think I have come to a conclusion after all.
When it is so frustratingly difficult to put into words the concept that I am examining, then I must entertain the possibility that the concept itself may be flawed. So back to the drawing board...
I have followed up a link that KazetN gave me :
http://en.wikipedia.org/wiki/Evolution_of_sexual_reproduction#Origin_of_sexual_reproduction
(Interesting enough, this link has the added caveat: More inputs required!)
Also: http://biologos.org/blog/evolution-and-the-origin-of-biological-information-part-5
A good article by Carl Zimmer on the evolution of sex in www.sciencemag.org of May 8, 2011
Here is the conclusion that I have come to, for what it's worth:
1 The first cells needed to replicate in order to propagate
2 This lead to various different forms of propagation at the cellular level, the mechanisms of which are not yet fully understood, but several theories presently exist.
I'm happy to leave it at that. I think we have exhausted this discussion. Thanks for your time and inputs.
😀
In peace
CJ
08 Aug 11
1 edit
Originally posted by CalJustIf that were true, then any one example would have been sufficient. But when an example seems to be be getting explained, you jump to a new example.
The reason why I keep jumping from one example to another, is because it is not any ONE system which intrigues me (insects, marsupials, what-have-you) but the concept that at least superficially, ANY reprodutive system can only reproduce in the way that itself was reproduced. So where do they all come from?
Yes, I can see the concept. But I disagree about its validity in the real world. Practically all reproductive systems have significant variation within a species, and even more significant variation across species. It is not true that change must be sudden and dramatic. We have countless examples of living things that demonstrate possible 'intermediary' systems between one known system and another.
That is also why the discussion about how a pouch got formed, or the fact that some marsupials have no pouches, is a red herring.
Not at all. You seemed to initially be claiming that the pouch was a required part of the system, yet now admit that it is not. This demonstrates that what you might think is a required part of a reproduction system may not be.
For example, you may think that the placenta in mammals is required and cant think of how it could have evolved. Yet there are some sharks that have also developed a basic placental system and others that give live birth but have no such system. We can see intermediaries. And I must note that the shark system evolved completely separately from the mammals.
Here is the conclusion that I have come to, for what it's worth:
1 The first cells needed to replicate in order to propagate
2 This lead to various different forms of propagation at the cellular level, the mechanisms of which are not yet fully understood, but several theories presently exist.
And I must add that cellular propagation is primarily asexual and long pre-dates sexual reproduction. If the billions of billions of cells that make up your body and have made up your body over your life span, only one, was a result of sexual reproduction.
Also, sexual reproduction is not the only way that organisms swap genes.
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08 Aug 11
Originally posted by CalJustAh, well, there you are wrong. Reproductive systems can evolve from other reproductive systems, in small steps.
The reason why I keep jumping from one example to another, is because it is not any ONE system which intrigues me (insects, marsupials, what-have-you) but the concept that at least superficially, ANY reprodutive system can only reproduce in the way that itself was reproduced.
For example, a system whereby the female lays eggs which are fertilised by the male, after the female has moved away, can very easily evolve into:
- one whereby the eggs are fertilised close to the female (because that means the female knows which male fertilsed the eggs, enabling her to actively select "better" partners), into
- one whereby the eggs are fertilised directly on the female's body;
- whereby the eggs are fertilised inside her body (both extensions of the former);
- where the fertilised egg is retained by the female until circumstances are safe for the egg;
- where the egg starts developing inside the female, making the laid egg even safer;
- where the egg develops entirely within the female (this is called oviviviparous);
- where the egg dispenses with the shell which was necessary when it still developed for some time outside the mother (which is, after all more efficient);
and now we've got from fish eggs to live births, all using small steps every one of which is perfectly tenable.
Note that I'm not claiming that live births did evolve this way (although AFAIAA something similar was in fact responsible), but it does show that one reproductive system can, in fact, evolve into another which is superficially very different.
Richard
08 Aug 11
Originally posted by CalJustI believe that this may very well be the case. The Bible does say that the foolishness of God is wiser than man's wisdom.
Without repeating his entire argument here, his conclusion is as follows: "Unless one is willing to take the position that God has placed these decapitated AREs in these precise positions to confuse and mislead us, the conclusion of a common ancestor for humans and mice is virtually inescapable."
Disclaimer: This was meant to be a Biblical perspective. Of course if you don't believe in the Bible's authority, then it will mean nothing to you and it was not meant for you.