On the Origin of Species - Chapter 9

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On the Origin of Species - Chapter 9

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Post by otseng »

What is Darwin's point in chapter 9?

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Post by otseng »

In chapter 9, Darwin asks a very good question - "Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory." In this chapter, he tries to give the explanation - imperfection of the geologic record. "The explanation lies, as I believe, in the extreme imperfection of the geological record."

He then spends some time to introduce Lyell's Principles of Geology. This work is a key foundation to Darwin's thesis and allows for Darwin to have the time necessary for natural selection to operate.

"I have made these few remarks because it is highly important for us to gain some notion, however imperfect, of the lapse of years. During each of these years, over the whole world, the land and the water has been peopled by hosts of living forms. What an infinite number of generations, which the mind cannot grasp, must have succeeded each other in the long roll of years!"

He then goes into part of the reason for the imperfection in that little has been explored.

"Only a small portion of the surface of the earth has been geologically explored, and no part with sufficient care, as the important discoveries made every year in Europe prove."

Another reason is because of how the stratas are formed. He states that there are only two ways that thick layers can form - either at shallow waters or in deep waters. Waters of moderate depth where there are wave action would not cause layers.

"Such thick and extensive accumulations of sediment may be formed in two ways; either, in profound depths of the sea ... or, sediment may be accumulated to any thickness and extent over a shallow bottom, if it continue slowly to subside."

I question both of these explanations. How can animal/plant remains (let alone terrestrial life) make its way to the depths of the sea and become buried? And what evidence is there that shallow bottoms can accumulate thick layers? Darwin states that they only way for this to happen is that it must subside at a rate similar to sediment accumulation. If it subsides faster, then wave action would then take effect. If it doesn't subside, then the layer would not be thick.

But he says, "I am convinced that all our ancient formations, which are rich in fossils, have thus been formed during subsidence." So, all these layers happen to have the same rate of subsidence and sedimentation at so many locations and for such a long period of time (thousands/millions of years)? Also, how were all these animals fossilized in shallow waters? Usually subsidence is a slow process, not an immediate event. So, if sedimentation is also then at the same rate, then the animals would more likely to decay than be buried.

Also, if thick layers are formed at shallow waters, why do we see land animals and non-aquatic plants in these thick layers?

One interesting fact which I was not aware of is "that very thick deposits are usually barren of organic remains, except near their upper or lower limits." He does not explain why this would be the case however.

He also mentions one of the most serious problems in the geologic record, the sudden appearance of life in the lowest fossiliferous layers. But, he does not have an answer for this.

"Consequently, if my theory be true, it is indisputable that before the lowest Silurian stratum was deposited, long periods elapsed, as long as, or probably far longer than, the whole interval from the Silurian age to the present day; and that during these vast, yet quite unknown, periods of time, the world swarmed with living creatures. To the question why we do not find records of these vast primordial periods, I can give no satisfactory answer."

Another interesting tidbit that he mentions: "Looking to the existing oceans, which are thrice as extensive as the land, we see them studded with many islands; but not one oceanic island is as yet known to afford even a remnant of any palaeozoic or secondary formation." Why does not such fossils exist?

And finally he mentions another very interesting fact. "All the most eminent palaeontologists, namely Cuvier, Owen, Agassiz, Barrande, Falconer, E. Forbes, &c., and all our greatest geologists, as Lyell, Murchison, Sedgwick, &c., have unanimously, often vehemently, maintained the immutability of species."

These scientists who studies fossils and geology looks at the data and comes to a different conclusion than Darwin. And when Darwin looks at the fossil record data, what he questions is not his own conclusion, but that the evidence from these scientists are lacking. And Darwin is then so bold as to end the chapter with this statement - "the difficulties above discussed are greatly diminished, or even disappear." Rather, the difficulties remain and that they are as strong as when he first acknowledged the problems.

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