Thursday, February 12, 2009

Part One

Darwin's Jig Saw Picture.
Part One:
In his Introduction to 'The Origin' Darwin wrote.
No one ought to feel surprise at much remaining as yet unexplained in regard to the origin of species and varieties, if he makes due allowance for our profound ignorance in regard to the mutual relations of all the beings which live around us. Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare? Yet these relations are of the highest importance, for they determine the present welfare, and, as I believe, the future success and modification of every inhabitant of this world. Still less do we know of the mutual relations of the innumerable inhabitants of the world during the many past geological epochs in its history. Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgement of which I am capable, that the view which most naturalists entertain, and which I formerly entertained, namely, that each species has been independently created is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification. [Charles Darwin' Introduction]
Well Darwin's great idea was like the way we often start a jigsaw puzzle by first doing all the edges of the picture and then leaving the rest to be filled in afterwards. Darwin was unable to fill in much of the picture though he had done much of the edge. It was left to others to start completing the picture. Many tried to put their 'discoveries' within the bounds of the puzzle but found they did not fit and were discarded. These included Lemarke and Lysenko. Even Darwin's pangenisis, Kelvin's estimation of the age of the earth, and those who support 'Intelligent design' must be discarded while others made a perfect fit.Those most notable are Gregor Johan Mendel, Wegener, Creek and James Watson and Alverez,although the latter may be disputed, itogether with those involved in the sequencing of genes in many species including man. It is not possible to put a finger on natural selection and say there that proves it, but the amount of information coming out now is just overwhelming. All the new discoveries reinforce it. There are many like Morgan and Muller, of whom the writer had never heard of. Simply put, and the idea is simple, like all great theories and solutions, is that plants and animals produce far more than can possibly survive, and that there is variation between the offspring and those which show some advantage survive over those that are not as well suited,and of course the surviving ones in turn must produce more offspring. Basically that is all there is to it. Darwin had many other theories within this concept which have turned out to be incorrect but that is irrelevant. He was so upset that Sir Charles Lyall his friend and mentor in Geology, seemed not to be able to tell the difference between Lemarke's theory an hism yet even he found himself doing the same because of his inability to find a theory for the passing on of the small differences that natural selection so depended on. And I must say it is very easy to make the same mistake. The difference can sometimes be very subtle. So then of course there are so very many many others doing patient paleontology research who have perhaps put in just one little piece, and more recently but of the greatest significance the considerable army of scientist involved in the Human Genome Project. But while Darwin's name is most notable in changing the way we think about ourselves those many before him were important as without their contributions to the knowledge of our world, Charles Darwin would not even have boarded the Beagle. We must look at the work of others that followed to see how we come to have a much more complete jigsaw picture.

The Distribution of Species.

In chapter twelve of 'The Origin' Darwin wrote;
New Zealand in its endemic plants is much more closely related to Australia, the nearest mainland, than to any other region: and this is what might have been expected; but it is also plainly related to South America, which, although the next nearest continent, is so enormously remote, that the fact becomes an anomaly. and from his conclusions. Turning to geographical distribution, the difficulties encountered on the theory of descent with modification are grave enough. All the individuals of the same species, and all the species of the same genus, or even higher group, must have descended from common parents; and therefore, in however distant and isolated parts of the world they are now found, they must in the course of successive generations have passed from some one part to the others. We are often wholly unable even to conjecture how this could have been effected.
Joseph Dalton Hooker [1817-1911] was to Botanical Evolution what Darwin was to Animal Evolution. He was a disciple of Darwin and was the first to learn about evolution through Natural Selection from Darwin himself, and kept the secret to himself for thirteen years."I am almost convinced," Darwin told Hooker, "that species are not (and he said 'it is like confessing a murder') immutable," adding that, "I think I have found out the simple way by which species become exquisitely adapted to various ends' (Burkhardt and Smith 1987: 2). This was was of course, natural selection, and Hooker was the first in the world to hear of Darwin’s secret. Hooker noted and discussed with Darwin the similarity between the plant species of Tasmania,New Zealand, Kerguelen Island, and Tirrra del Feugo, to which Darwin gave an unsatisfactory explanation and called it an anomaly. The Podocarpus genus is found in South America, South Africa, Australia and New Zealand. In South Africa Podocarpus falcatus is very similar to the Podarcarpus species, Totora, and is just one example. Continental Drift. The solution to this anomaly was left to Wegener who first presented an explanation of this in his theory in lectures in 1912 and published it in full in 1915 in his most important work, Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He searched the scientific literature for geological and paleontological evidence that would buttress his theory, and he was able to point to many closely related fossil organisms and similar rock strata that occurred on widely separated continents, particularly those found in both the Americas and in Africa. Wegener's Theory of continental drift won some adherents in the ensuing decade, but his postulations of the driving forces behind the continents' movement seemed implausible. By 1930 his theory had been rejected by most geologists, and it sank into obscurity for the next few decades, only to be resurrected as part of the theory of plate tectonics (q.v.) during the 1960s. [Encyclopedia Britanica] Wegener's proposition was attentively received by many European geologists, and in England Arthur Holmes pointed out that the lack of a driving force was hardly sufficient grounds to scuttle the entire continental drift and won some adherents in the ensuing decade, but his postulations of the driving forces behind the continents' movement seemed implausible. As early as 1929, Holmes proposed an alternative mechanism--namely, convection of the mantle, which remains today a serious candidate for the force driving the plates. Wegener's ideas also were appreciated by geologists in the Southern Hemisphere. One of them, the South African Alexander Du Toit, remained a lifelong believer. After Wegener's death, Du Toit continued to amass further evidence in support of continental drift. [Alexander Du Toit, a South African geologist, in "Our Wandering Continents" (1937),] Of course South America, Africa ,Antarctica,and Australasia were all joined together as one great continent

. The Age of the Earth .

Darwin was worried about the objections concerning the time required for evolution to have taken place
On the lapse of Time. Independently of our not finding fossil remains of such infinitely numerous connecting links, it may be objected, that time will not have sufficed for so great an amount of organic change, all changes having been effected very slowly through natural selection. It is hardly possible for me even to recall to the reader, who may not be a practical geologist, the facts leading the mind feebly to comprehend the lapse of time. He who can read Sir Charles Lyell's grand work on the Principles of Geology, which the future historian will recognise as having produced a revolution in natural science, yet does not admit how incomprehensibly has been the past periods of time, may at once close this volume.
Kelvin was one who was to object and throw a spanner in the works. 'The answer of 25 million years found by Kelvin was not received favorably by geologists. Both the physical geologists and paleontologists could point to evidence that much more time was needed to produce what they saw in the stratigraphic and fossil records. As one answer to his critics, Kelvin produced a completely independent estimate -- this time for the age of the sun. His result was in close agreement with his estimate of the age of the earth. The solar estimate was based on the idea that the energy supply for the solar radiative flux is gravitational contraction. These two independent and agreeing estimates of the age of two primary members of the solar system formed a strong case for the correctness of his answer. As we now know, both of Kelvin's answers were wrong, for reasons that he could not have known. In the case of the earth, the energy released in the crust by the decay of radioactive elements is sufficient to enhance significantly the geothermal flux. This larger flux then causes Kelvin's theory to predict a earth too young. In the case of the sun, Kelvin had no way of knowing that the energy source is nuclear fusion, for which there is fuel enough for at least 5 x 10 9 years. That Kelvin was wrong does not change at all that what he did was good science. His pioneering of the quantitative'{From the internet]

On Extinction
We have as yet spoken only incidentally of the disappearance of species and of groups of species. On the theory of natural selection the extinction of old forms and the production of new and improved forms are intimately connected together. The old notion of all the inhabitants of the earth having been swept away at successive periods by catastrophes, is very generally given up, even by those geologists, as Elie de Beaumont, Murchison, Barrande, &c., whose general views would naturally lead them to this conclusion. On the contrary, we have every reason to believe, from the study of the tertiary formations, that species and groups of species gradually disappear, one after another, first from one spot, then from another, and finally from the world. [Chapter 10 - On The Geological Succession of Organic Beings]
Darwin understood his theory as being a very gradual change over a vast period of time. He accepted that great advances would be made but of course he did not know where these advances would be. He would have been excited to learn about the discoveries concerning the causes of great extinctions such as the K-T Event. In fact there have been five great estinctions and the biggest of these mass extinctions 251 million years ago marking the boundry between the permian and triassic period. At this stage the cause of which can only be guessed at. However the extinction of sixty five million years ago is now fairly well documented. I copy what I have found on the internet concering the K-T mass extinction, also known as the Alvarez Event. Sixty-five million years ago about 70% of all species then living on Earth disappeared within a very short period. The disappearances included the last of the great dinosaurs. Paleontologists speculated and theorized for many years about what could have caused this "mass extinction," known, as the K-T event (Cretaceous-Tertiary Mass Extinction event). Then in 1980 Alvarez, Alvarez, Asaro, and Michel reported their discovery that the peculiar sedimentary clay layer that was laid down at the time of the extinction showed an enormous amount of the rare element iridium. First seen in the layer near Gubbio, Italy, the same enhancement was soon discovered to be world wide in that one particular 1-cm (0.4-in.) layer, both on land and at sea. The Alvarez team suggested that the enhancement was the product of a huge asteroid impact. On Earth most of the iridium and a number of other rare elements such as platinum, osmium, ruthenium, rhodium, and palladium are believed tohave been carried down into Earth's core, along with much of the iron, when Earth was largely molten. Primitive "chondritic" meteorites (and presumably their asteroidial parents) still have the primordial solar system abundances of these elements. A chondritic asteroid 10 km (6 mi.) in diameter would contain enough iridium to account for the worldwide clay layer enhancement. This enhancement appears to hold for the other elements mentioned as well. Since the original discovery, many other pieces of evidence have come to light that strongly support the impact theory. The high temperatures generated by the impact would have caused enormous fires, and indeed soot is found in the boundary clays. A physically altered form of the mineral quartz that can only be formed by the very high pressures associated with impacts has been found in the K-T layer. Geologists who preferred other explanations for the K-T event said, "show us the crater." In 1990 a cosmochemist named Alan Hildebrand became aware of geophysical data taken 10 years earlier by geophysicists looking for oil in the Yucatan region of Mexico. There a 180-km (112-mi.) diameter ring structure called "Chicxulub" seemed to fit what would be expected from a 65-million-year-old impact, and further studies have largely served to confirm its impact origin. The Chicxulub crater has been age dated (by the 40Ar/39Ar method) at 65 million years! Such an impact would cause enormous tidal waves, and evidence of just such waves at about that time has been found all around the Gulf. One can never prove that an asteroid impact "killed the dinosaurs." Many species of dinosaurs (and smaller flora and fauna) had in fact died out over the millions of years preceding the K-T events. The impact of a 10-km asteroid would most certainly have been an enormous insult to life on Earth. Locally, there would have been enormous shock wave heating and fires, tremendous earthquake, hurricane winds, and trillions of tons of debris thrown everywhere. It would have created months of darkness and cooler temperatures globally. There would have been concentrated nitric acid rains worldwide. Sulfuric acid aerosols may have cooled Earth for years. Life certainly could not have been easy for those species which did survive. Fortunately such impacts occur only about once every hundred million years. A whole new world of paleontology has been opened up in the last decade which changes the way Darwin envisioned the process of evolution by natural selection though it must be said that the rate is really relative. After each mass extinction life seemed to have been so stunned that change occurred very slowly at first then gradually gathering speed till it reached a stage of stability which then lasted for millions of years.Within this stability there was always change

The Geological Record and Intermediates. From Darwins Conclusions:
The noble science of Geology loses glory from the extreme imperfection of the record. The crust of the earth with its embedded remains must not be looked at as a well-filled museum, but as a poor collection made at hazard and at rare intervals. The accumulation of each great fossiliferous formation will be recognised as having depended on an unusual concurrence of circumstances, and the blank intervals between the successive stages as having been of vast duration. But we shall be able to gauge with some security the duration of these intervals by a comparison of the preceding and succeeding organic forms.
Most of the work done by fossil hunters covers still a very small portion of the Earth's crust and so much remains to be discovered.Unfortunately though much has been lost through erosion and movement of the land masses. There would have to be really new thinking if a elephant fossil was found amongst the dinosaur fossils without good reason. Fossils are found in the right geological place and not where you would not expect them to be found.. Intermediate forms are not the successful ones and are rare. Considering the number of individuals that have inhabited the earth, the number of fossils are few indeed.As it is understood at present the explosion of types of animals after the great extinctions was fairly rapid and occupied only a few million years, followed by very long periods of virtual stability occupying tens of millions of years. It was more likely that fossils came from the stable periods as the we occupied the greatest time period.


Post a Comment

Subscribe to Post Comments [Atom]

<< Home