Hi Pistike,
hope it is okay to let you wait - appear as often as I can!
Okay, I see that the discussion must now inevitably follow the familiar route - my next question must be the fossil record, right? That is, if you say "cumulative series of steps" over those millions of years, one would expect to find an uninterrupted row of fossils of these intermediates. Are they here?
There are plenty of fossils of
intermediate forms between prehistoric fish and prehistoric land animals. ...
I was just FISHING online and found an interesting quote:
"Although the relationship of the rhipidistians to the amphibians will be discussed in greater detail in the next chapter, it should be said here that none of the known fishes is thought to be directly ancestral to the earliest land vertebrates. Most of them lived after the first amphibians appeared, and those that came before show no evidence of developing the stout limbs and ribs that characterized the primitive tetrapods."
(Stahl, Barbara J. [Professor of Biology, Saint Anselm College, USA], "Vertebrate history: Problems in Evolution," Dover: New York NY, 1985, p.148)
What may it actually mean? I think the two following takes might be interesting.
An example presented in the low right corner of your scheme, COELACANTH, was believed to be an evolutionary ancestor of tetrapods, that's right. But, it was caught alive in the Indian Ocean in 1938.
It is a very massive deep-water fish, with really bony fins, but it neither uses them for walking, nor it even comes close to the water surface. It did not evolve since Devonian in anything different than it was. Thus it is neither fishapod, nor missing link, nor even an extinct species.
Tiktaalik is a really very interesting and spectacular case. The fossil was found in 2006 in Arctic Canada and was proudly presented as a true missing link between devonian fishes and tetrapods ( that's why fishapods ). So, Internet is really full of evolutionist sites, presenting it as that, and of the creationist sites, stating, of course, the contrary. I have tried to find some analysis of the found , and got here:
http://www.wort-und-wissen.de/index2.../sij132-6.html
Sorry, it is in German, but the schemes represented are quite understandable. The article written by Dr. Reinhard Junker.
The essense in short:
TIKTALIIK was claimed to fill the gap between the first known tetrapods and their fishy contemporaries ( see the scheme ). Analysis of the front extremities of TIKTALIIK shows that they don't show any signs of transformation in the "desired" direction - they are fins, no signs of digits. The same goes to the scull. So, seen from an evolutionary perspective, TIKTALIIK could show, at best, another branch of evolution. But in this case, it does not only not fills the existing gap in the fossil record, but produces another two.
Moreover, the rear extremities of TIKTALIIK, and the tail, were not found. So the reconstruction, as that in Wikipedia , is based on a supposition how it SHOULD LOOK LIKE to fill in the gap. This is important, because it means , actually - could it walk? You know that we need LEGS for walking, these are not ARMS, because legs are attached to the backbone via pelvic bones, and such construction carries, actually , the weight of the body ( by me, by you, by apes, T-Rex....) . The fins of the fish are not of this kind. The logical hypothesis is that the rear fins of TIKTALIIK were not legs as all other details do not show it, and even the reconstruction does not. So, much says to the supposition that it was just a fish species, living by a coastline and feeding of insects etc, like also many modern species do. After this niche had closed ( and what did it look like in Devonian, one can only speculate ), TIKTALIIK had become extinct. That's all.
[quote]
Does Carl Zimmer explain what were the pressures which made the fish to leave its normal environment?
First and foremost, the land was full of plant life that made easy prey for adventurous fish forms.
The evolutionary process is certainly still happening today.
I have some troubles to bring these two points of you together.
First, the land is full of plant and insect life today no less than it was millions of years ago. So, the pressures must be actually the same. There are lots of fish species living, as well - the half of all vertebrates ! There are certainly some adventurous species among them. Can you name some visible examples of fish on its way to tetrapod known today? If you say, evolution ( let us make it clear, it sounds like macroevolution for me ) happens now, as well as in Devonian, the examples must be all-present. Each living species of course prefers it, to live in its own niche. If this niche is being closed for whatever reason, the species would migrate or become extinct, that is what the modern observations show. Why should it have been different millions of years ago?
I can name also , if you want, of course, some examples of really EXTREME pressures, which the known species undergo since thousands of years and still do not show any signs of evolution.
AR:The last question ( for today !) - can you give your opinion on how life has started? Is abiogenesis possible or not? Just interested how you see it.
PG: This question doesn't deal with evolution, strictly speaking. How life initially came about has no real bearing on the question of the common ancestry of all life on Earth.
You are right, it doesn't, sorry I was a little bit provocative
Still, the question was significant for Haeckel, who understood the primitive life as a drop of jelly. It was important for Miller and Urey, who hoped to show in 1953 how the life begun but failed. The question is regarded as secondary by the modern ET, just because it can not answer it. Looks like the materialistic science stumbles at its very first step, and continues to walk further, as if nothing happened.
Very sincerely,
Andrew