[my post snipped]
>Due to the shuffling of genes, the phenomenon of cross-over etc. sexual
>reproduction can produce a tremendously more genetically varied group of
>organisms than can asexual reproduction. Thus when a virus comes along, a
>few more of the sexually reproduced organisms have immunity. If everybody
>has the same genome then if one individual has no resistance, probably no
>one does. Genetic similarity is becoming a concern in the agricultural
>community. Many of the wheats, ryes, rices, cows, sheep etc are becoming
>genetically impoverished compared with their wild cousins. Because of
>this, some professional worriers are becoming worried that an entire crop
>could be wiped out quickly by one disease.
I see, I guess it would be a huge advantage to have a more varied gene
pool, but I still don't understand the mechanism that would initiate sexual
reprodution in the first place. How did sexual reprodution develope?
The thing about the egg developing was intersting, and I see your point,
but I think that it is one of those cases where based on the assumption
that evolution happened, it seems possible. Without that assumption, a
conclusion couldn't be reached. Makes it harder to know what to think,
because if evolution was true, then there would be lots of question
answered by saying, "evolution happened, and they're here now, so they must
have evolved, so here's one way it could have happened". Unfortunately, I
don't think its that clear cut, or at least I haven't grasped it yet, which
makes it hard to know what to do about that kind of assumption.
>
>
>>
>>>And how something would evolve from
>>>>laying eggs in water to laying eggs on land, to not laying eggs at all!
>>>
>>>Each form of reproduction works in the peculiar environment to aid in the
>>>survival of the species.
>>
>>Lets imagine an amphibian, who lays eggs in the water. How would this beast
>>change from laying eggs in the water to laying eggs on land? The structure
>>of the egg would have to change, the baby would have to change to be able
>>to escape the new type of egg, the babys would have to be able to handle
>>the land, and the egg laying process would have to change....
>
>Lets look at what fossils are actually there and what the environment of
>the earliest amniotes inhabited. First off, you must remember that fossil
>eggs are very rare, even in the Pleistocene. Robert Carroll, Vertebrate
>Paleontology and Evolution, 1988 (still a widespread text as I bought it
>last year) says that the earliest amniote animals are found in the lower
>Pennsylvanian of Nova Scotia (p. 193) It was about 10-12 cm long about the
>same size as modern plethodontid salamnders that lay their eggs on land.
>(p. 193, 194, 197) These salamanders hatch fully formed from eggs. The
>eggs lack a extraembryonic membrane. According to Carroll, this limits
>effective exchange of gas and water and limits the size of the egg.
>Support against the force of gravity also limits the size of the egg
>(imagine taking a chicken egg sans shell and laying it on the ground. It
>would squish like a large water balloon laid on the ground.)
>
>Support for this idea comes from the earliest egg found in the fossil
>record. It is from the Lower Permian. It lacks a calcareous shell ( p.
>198) But because of this lack some have suggested that it is not an egg but
>most paleontologists apparently accept it. (Edwin H. Colbert, Evolution of
>the Vertebrates, (New York: John Wiley and Sons, 1969), p. 110; George
>Gaylord Simpson, Fossils and the History of Life, Scientific American
>Books, 1983, p. 86)
>
>Now, what kind of environment did the earliest amphibians live? Along the
>moist shores. These are exactly the type of land that modern salamanders
>above live and are able to lay their eggs on land. How do we know that they
>lived in these humid environments? Because of the other animals they lived
>with.
>
>""Logan's 'Division 4', with a thickness of 2,539 feet, is the main
>fossiliferous horizon with coal formation, and often abounds in fresh-water
>bivalves, air-breathing snails, bivalve crustaceans, tiny worm tubes, and
>bones and tracks of Amphibia; even rain-drop impressions are
>preserved."~Louis V. Pirrson and Charles Schuchert, Textbook of Geology,
>(New York: John Wiley and Sons, 1920), p. 783-784.
>
>The environment is consistent with the presumed development of the egg.
>
>>
>>Could all this happen in one go? If not, what kind of changes could bring
>>this about?
>
>No, it didnt' happen in one go. Robert Carroll says
>
> "According to Szarski, the first of the extraembryonic membranes to
>evolve would have been the allantois. In modern amniotes, it develops as a
>bladder to retain water that is otherwise lost from the embryo. Solutes
>within the urine render its contents hypertonic relative to fresh water.
>If the egg is laid on damp ground, water is drawn into the allantois by
>osmosis. In modern reptiles such as many lizards and turtles that have
>permeable egg shells, the water content within the egg may more than double
>during development because because of absorption into the allantois.
> With the development and enlargement of the allantois, the more
>superficial layers of tissue that covered the embryo in the primitive state
>were forced out from their original position and reflected over the body.
>These layers form the chorion, which together with the surface of the
>allantois serves for gas exchange. A further membrane, the amnion, forms a
>fluid-filled chamber that surrounds the embryo. In order to fertilize eggs
>laid on land, internal fertilization probably evolved early in amniote
>evolution. Since copulatory organs are absent in the primitive living genus
>Sphenodon and have apparently evolved separately in the ancestors of
>lizards and crocodiles, they were almost certainly absent in the early
>amniotes.
> "A permeable membranous shell presumably evolved in conjunction with the
>extraembryonic membranes. An object that was presumed to be the oldest
>amniote eggs was described from the Lower Permian of Texas, but it lacks a
>calcareous shell and the evidence that it is an egg is equivocal." Robert
>J. Carroll, Vertebrate Paleontology and Evolution, (New York: W.H. Freeman,
>1988), p. 197-198
>
>>
>>>>And why do bird have pretty colors? This is attractive to other birds, but
>>>>it would also make them obvious to preditors.
>>>
>>>Not necessarily. Sometimes what we see as pretty colors are not the same
>>>frequencies that the eyes of other species see.
>>>
>>>Wouldn't natural selection
>>>>have made animals attracted to each other for qualities like camoflage,
>>>>strength and speed, not things like a huge stupid peacock tail that slows
>>>>you down?
>>>
>>>Then why did God create the stupid peacock tail feathers?
>>
>>
>>I believe in a God who likes beauty, thats why we have art, because out
>>creator has made beauty and made us to appreciate it. Peacock feathers are
>>rad, I think they are heaps beautiful, and I'm sure God made them with that
>>in mind.
>
>Could it be that He also made them so that peacocks would be easy prey for
>the predators? After all, it doesn't say in Scripture that God created
>them for beauty but it does say:
>
>Psalm 104:21 The young lions roar after their prey, and seek their meat
>from God.
>
>So I would conclude that your speculation that God made peacock feathers
>for beauty is not as plausible as believing that God created them to slow
>the peacock down.
>
You got me again, thats a good point that I didn't think of. Cool, it's
good to learn!
Donald
____________________________________________
Donald Howes
Acting Research Systems Co-ordinator
Research Services
University of New England
Ph 6773 3263
"I am not ashamed of the gospel, because it is the power of God for the
salvation of everyone who believes" Romans 1:16
_____________________________________________