08 May 06
Originally posted by CalJustActually, you brought up the chicken and egg thing, not me.
[b]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, ...[text shortened]... what were the intermediary steps from this non-egg-laying creature to the egg-laying creature?
[/b]
So, it seems that you are actually asking about the evolution of sex. Well, it's less odd that you might initially think. Even bacteria have "sex". Although with them it's more of a simple genetic exchange. If, during the early evolution of animals, this type of genetic exchange led to organisms with a higher fitness (and Mat Ridley, amongst other evolutionary biologists, seems to think that sex is a defense mechanism against parasites, so that'd be a "yes" then (see his book "the red queen hypothesis"😉 then it'd be favoured. Meiotic division isn't so distantly dissociated from normal mitotic division that initially it couldn't simply have been a genetic error which prevented genome replication before chromosome segragation, leading to 1n cells being produced instead of the regular 2n cells (a little technical i know, sorry). "Sperm" and "eggs" are really just generic terms that we use for "little sex cell" and "big sex cell" respectively. Initially, all organisms within a species would be very similar, however, the two sexes would diverge, with one parent making smaller and smaller gametes over time, and the other increasing their investment.
That's the basic pattern anyway (that can still be seen in a variety of organisms today). Feel free to stay or go as you wish.
08 May 06
Originally posted by slappy115Platypus and Echidna, both have hard shelled eggs. Both are monotremes. Found in Australia and Papua New Guinea.
All 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.
09 May 06
Originally posted by CalJustSo 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??
[b]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 m ...[text shortened]... of, its evolution.
Maybe it’s time for me to disappear again for a year or two….
CJ[/b]
No. I'll draw out a rough cladogram here. A cladogram is a diagram showing a postulated order of evolution.
Eukaryotic Cell
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Sexual Reproduction
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Multicellular Organism
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Worm
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Amphibian
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Reptile ---- Mammal
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Bird
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Chicken
Get it? Sex evolved way before chickens did.
09 May 06
Originally posted by AThousandYoungYou forgot about prokaryotes.
[b]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??
No. I'll draw out a rough cladogram here. A cladogram is a diagram showing a ...[text shortened]...
l
Bird
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Chicken
Get it? Sex evolved way before chickens did.[/b]
09 May 06
Originally posted by AThousandYoungActually, birds are the next step in evolution. I don't think mammals split off at reptiles. Although come to think of it, there were mammals and dinosaurs.
No, I just didn't go back that far in the past.
Prokarotic Cell
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Eukaryotic Cell
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Sexual Reproduction
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Multicellular Organism
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Worm
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Amphibian
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Reptile ---- Mammal
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Bird
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Chicken
09 May 06
Originally posted by scottishinnzThe way I see it is that reptiles have scales while birds have scales, to a diminished level. Won't it be possible that mammals and birds divereged at a point where one couldn't fly while the other one could?
No, mammals and birds are not directly related. The last common ancestor was a reptile.
09 May 06
Originally posted by slappy115The differences in the respiratory systems of mammals and birds (v. efficient, as it works as a loop), along with skeletal morphology would suggest otherwise.
The way I see it is that reptiles have scales while birds have scales, to a diminished level. Won't it be possible that mammals and birds divereged at a point where one couldn't fly while the other one could?
09 May 06
Originally posted by scottishinnzI understand how a bird's respiratory system works with the chambers in the bones and how one breathe acts like two and such. With the morphology of the bones, dinosaurs were reptiles. Some began to look as birds. I guess if there is no dinosaur that resembles a mammal, I can't argue any further.
The differences in the respiratory systems of mammals and birds (v. efficient, as it works as a loop), along with skeletal morphology would suggest otherwise.
10 May 06
2 edits
Originally posted by slappy115Mammals evolved from synapsids. They branched off from other reptiles about 320 mya. Birds evolved from the therapod dinosaurs which first appeared 100 million years later. The therapods came from the dyapsids. Mammals and birds did not evolve one to the other but both from reptiles. If you're interested, look up synapsids and diapsids. These were among the first ancestors of each which the other does not share.
The way I see it is that reptiles have scales while birds have scales, to a diminished level. Won't it be possible that mammals and birds divereged at a point where one couldn't fly while the other one could?
http://en.wikipedia.org/wiki/Synapsida
http://en.wikipedia.org/wiki/Diapsid
10 May 06
Originally posted by AThousandYoungthanks, i were meaning to answer this yesterday, but got caught up in some of that pesky work stuff....
Mammals evolved from synapsids. They branched off from other reptiles about 320 mya. Birds evolved from the therapod dinosaurs which first appeared 100 million years later. The therapods came from the dyapsids. Mammals and birds did not evolve one to the other but both from reptiles. If you're interested, look up synapsids and diapsids. These were amo ...[text shortened]... .
http://en.wikipedia.org/wiki/Synapsida
http://en.wikipedia.org/wiki/Diapsid
10 May 06
Originally posted by AThousandYoungI'm interested by how you would explain the evolution from asexual to sexual reproduction.
No, I just didn't go back that far in the past.
Prokarotic Cell
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Eukaryotic Cell
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Sexual Reproduction
l
Multicellular Organism
l
Worm
l
Amphibian
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Reptile ---- Mammal
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Bird
l
Chicken