Presentation on theme: "Evolution The Origin of the Species. Before Darwin’s Evolutionary Theory In the 1700’s the study of fossils proved the existence of old organisms different."— Presentation transcript:
Evolution The Origin of the Species
Before Darwin’s Evolutionary Theory In the 1700’s the study of fossils proved the existence of old organisms different from those found before then. This suggested that living species had undergone changes over time. The naturalist Georges Louis Buffon ( ) thought that living forms had originated from a small number of ancestors.
Erasmus Darwin Prominent English physician, grandfather of the naturalist Charles Darwin. He believed that species modified themselves by adapting to their environment in a purposive way. It is as a transitional figure that Erasmus Darwin is primarily important. He embodied the attitudes and values of 18th-century materialism, but his conclusions concerning evolution were drawn from simple observation and were rejected by the more sophisticated of the 19th-century scientists, his grandson Charles foremost among them.
Jean-Baptiste Lamarck Jean-Baptiste-Pierre-Antoine de Monet, Chevalier de Lamarck pioneer French biologist who is best known for his idea that acquired traits are inheritable, an idea known as Lamarckism, which is controverted by Darwinian theory.
Cuvier By rejecting the 18th-century method of arranging animals in a continuous series in favour of classifying them in four separate groups, he raised the key question of why animals were anatomically different. Although Cuvier's doctrine of catastrophism did not last, he did set the science of palaeontology on a firm, empirical foundation. He did this by introducing fossils into zoological classification, showing the progressive relation between rock strata and their fossil remains, and by demonstrating, in his comparative anatomy and his reconstructions of fossil skeletons, the importance of functional and anatomical relationships
Charles Darwin Charles Robert Darwin (12 February 1809 – 19 April 1882) was an English naturalist who achieved lasting fame by producing considerable evidence that species originated through evolutionary change, at the same time proposing the scientific theory that natural selection is the mechanism by which such change occurs. This theory is now considered a cornerstone of biology.
Charles Darwin Darwin developed an interest in natural history while studying first medicine, then theology, at university. Darwin's observations on his five- year voyage on the Beagle brought him eminence as a geologist and fame as a popular author. His biological finds led him to study the transmutation of species and in 1838 he conceived his theory of natural selection. Fully aware that others had been severely punished for such "heretical" ideas, he confided only in his closest friends and continued his research to meet anticipated objections. However, in 1858 the information that Alfred Russel Wallace had developed a similar theory forced an early joint publication of the theory.
Darwin’s Evolutionary Theory Lyell was a Scottish geologist largely responsible for the general acceptance of the view that all features of the Earth's surface are produced by physical, chemical, and biological processes through long periods of geological time. The concept was called uniformitarianism (initially set forth by James Hutton). Lyell's achievements laid the foundations for evolutionary biology as well as for an understanding of the Earth's development.
Darwin’s Evolutionary Theory Darwin's theory of evolution has four main parts: a. Organisms have changed over time, and the ones living today are different from those that lived in the past. Furthermore, many organisms that once lived are now extinct. The world is not constant, but changing. The fossil record provided ample evidence for this view. b. All organisms are derived from common ancestors by a process of branching. Over time, populations split into different species, which are related because they are descended from a common ancestor. Thus, if one goes far enough back in time, any pair of organisms has a common ancestor. This explained the similarities of organisms that were classified together -- they were similar because of shared traits inherited from their common ancestor. It also explained why similar species tended to occur in the same geographic region. c. Change is gradual and slow, taking place over a long time. This was supported by the fossil record, and was consistent with the fact that no naturalist had observed the sudden appearance of a new species. d. The mechanism of evolutionary change was natural selection. This was the most important and revolutionary part of Darwin's theory, and it deserves to be considered in greater detail.
The Voyage on the Beagle Charles Darwin sailed from Plymouth on the 27 December 1831 on a journey that was to take him many thousands of miles. He sailed in a ship called the Beagle. The Beagle was not a big ship, it was only about 28 metres long and had to be home to 74 people for the whole voyage.
The Voyage on the Beagle
The Development of a Theory During the voyage Darwin discovered that the animals on the Galapagos Islands were not quite like the animals he had seen in South America. In some ways the lizards were the same as those in South America but were different in others. Darwin also observed this to be the same with the many different types of finches on the islands. They were different from the finches he had seen in South America.
The Development of a Theory Darwin then found out something even more important. A tortoise or finch on one island was not quite like a tortoise or a finch on another island. By looking at the shell of a tortoise or the beak of a finch you could tell which island it had come from. All the finches had dull coloured feathers and short tails. They all laid four pink and white eggs in nests with small roofs. The difference was they all had different beaks. On one island they had strong thick beaks for cracking open nuts and seeds. On another island eighty kilometres away they had long thin beaks for catching insects.
The Origin of the Species First published on November 24, 1859, The Origin of Species (full title On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life) by English naturalist Charles Darwin is one of the pivotal works in scientific history, and arguably the pre- eminent work in biology. In it, Darwin makes "one long argument" for his theory that "groups" of organisms, rather than individual organisms, gradually evolve through the process of natural selection—a mechanism effectively introduced to the public at large by the book. The work presents detailed scientific evidence he had accumulated both on the Voyage of the Beagle in the 1830s and since his return.
Natural Selection Natural selection is the process that results in the adaptation of an organism to its environment by means of selectively reproducing changes in its genotype, or genetic constitution. In natural selection, those variations in the genotype that increase an organism's chances of survival and procreation are preserved and multiplied from generation to generation at the expense of less advantageous ones. Evolution often occurs as a consequence of this process. Natural selection may arise from differences in survival, in fertility, in rate of development, in mating success, or in any other aspect of the life cycle. All such differences result in natural selection to the extent that they affect the number of progeny an organism leaves.
Artificial Selection Close and constant observation of selective breeding of animals and plants gave Darwin substantial proof to his theory.
According to Darwin species evolved from a common ancient ancestor, through modification. Natural selection was the process which brought about new species.
Types of Selection A. Stabilizing selection Natural selection can be studied by analyzing its effects on changing gene frequencies; but it can also be explored by examining its effects on the observable characteristics—or phenotypes—of individuals in a population. Distribution scales of phenotypic traits such as height, weight, number of progeny, or longevity typically show greater numbers of individuals with intermediate values and fewer and fewer toward the extremes (the so-called normal distribution). When individuals with intermediate phenotypes are favoured and extreme phenotypes are selected against, the selection is said to be stabilizing.
B. Directional selection The distribution of phenotypes in a population sometimes changes systematically in a particular direction. The physical and biological aspects of the environment are continuously changing, and over long periods of time the changes may be substantial. The climate and even the configuration of the land or waters vary incessantly. Changes also take place in the biotic conditions; that is, in the other organisms present, whether predators, prey, parasites, or competitors. Genetic changes occur as a consequence, because the genotypic fitnesses may be shifted so that different sets of alleles are favoured. The opportunity for directional selection also arises when organisms colonize new environments where the conditions are different from those of their original habitat. In addition, the appearance of a new favourable allele or a new genetic combination may prompt directional changes, as the new genetic constitution replaces the preexisting one.
C. Diversifying Natural Selection Diversifying, or dynamic, natural selection is one of the important and basic processes by which evolutionary changes occur. Under conditions of changing environmental pressure, advantageous genotypes will be assimilated into the gene pool, and those individuals within the population who have superior fitness will leave more numerous offspring than those without.
Sexual Selection Mutual attraction between the sexes is an important factor in reproduction. The males and females of many animal species are similar in size and shape except for the sexual organs and secondary sexual characteristics such as the breasts of female mammals. There are, however, species in which the sexes exhibit striking dimorphism. Particularly in birds and mammals, the males are often larger and stronger, more brightly coloured, or endowed with conspicuous adornments. But bright colours make animals more visible to predators; the long plumage of male peacocks and birds of paradise and the enormous antlers of aged male deer are cumbersome loads in the best of cases. Darwin knew that natural selection could not be expected to favour the evolution of disadvantageous traits, and he was able to offer a solution to this problem. He proposed that such traits arise by “sexual selection,” which “depends not on a struggle for existence in relation to other organic beings or to external conditions, but on a struggle between the individuals of one sex, generally the males, for the possession of the other sex.”
Sexual Selection The concept of sexual selection as a special form of natural selection is easily explained. Other things being equal, organisms more proficient in securing mates have higher fitness. There are two general circumstances leading to sexual selection. One is the preference of one sex (often the females) for individuals of the other sex that exhibit certain traits; the other is increased strength (usually among the males) that yields greater success in securing mates.
Sexual Selection The presence of a particular trait among the members of one sex can make them somehow more attractive to the opposite sex. This type of “sex appeal” has been experimentally demonstrated in all sorts of animals, from vinegar flies to pigeons, mice, dogs, and rhesus monkeys. When, for example, Drosophila flies, some with yellow bodies and others with the normal yellowish-gray pigmentation, are placed together, normal males are preferred over yellow males by females with either body colour.
Proofs of Evolution Fossils are considered proofs of the theory of evolu tion.
The findings of various forms of fossils show that evolution takes place in a chronological order.
Through fossils it is possible to link the species to their extinct ancestors.
Proofs confirming the Evolutionary Theory: I. Biogeography Biogeography is the study of the patterns of distribution of animals and plants. It looks for general principles to explain how and why organisms are distributed the way they are locally or regionally as well as worldwide. Biogeography uses information from ecology and evolutionary biology as well as from geology (study of origin and structure of the Earth), paleontology (study of fossils), and climatology (study of the world's climates).
II. Comparative Anatomy Comparative anatomy is the study of similarities and differences in the anatomy of organisms. Two major concepts of comparative anatomy are: Homologous structures - structures (body parts/anatomy) which are similar in different species because the species have common descent. They may or may not perform the same function. An example is the forelimb structure shared by humans, cats, whales and bats.
III. Comparative Embryology: One of the marvels of nature is the way in which a complex organism develops from a single cell. The fully formed organism, however, is not produced in an instant. It is the outcome of a number of increasingly intricate changes occurring over a protracted period of time. This sequence takes place in the very young organism—the embryo. The study of the embryo's formation and development is a branch of biology called embryology.
IV. Comparative Anatomy Analogous structures - structures which are similar in different organisms because they evolved in a similar environment, rather than were inherited from a recent common ancestor. They usually serve the same or similar purposes. An example is the torpedo body shape of porpoises and sharks. It evolved in a water environment, but the animals have different ancestors.
Many vertebrates share the same structure at the embryonic stage (as seen in the picture: chicken embryo and human embryo) Coda
V: Evolutionary Biology Evolutionary biology seeks to answer questions about the origin and the genetic relationships of plants and animals, including the origin of humans. Evolutionary biologists examine relationships between organisms by means of comparative studies within any of the previously named fields of biology or through paleontology. Comparative studies reveal differences and similarities between species or higher taxonomic units.
VI. Molecular Biology Molecular Biology is the field of science concerned with studying the chemical structures and processes of biological phenomena at the molecular level. The discipline is particularly concerned with the study of proteins, nucleic acids, and enzymes— i.e., the macromolecules that are essential to life processes. The discipline seeks to understand the molecular basis of genetic processes; molecular biologists map the location of genes on specific chromosomes, associate these genes with particular characters of an organism, and use recombinant-DNA technology to isolate and modify specific genes.
Extinction Extinction occurs when a species can no longer reproduce at replacement levels. Most extinctions are thought to have resulted from environmental changes that affected the species in either of two ways. The doomed species might not have been able to adapt to the changed environment and thus perished without descendants; or it may have adapted but, in the process, may have evolved into a distinctly new species. The effect of humans on the environment, through hunting, collecting, and habitat destruction, has become a significant factor in plant and animal extinctions.
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