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Encyclopedia > History of zoology (after Darwin)

Zoology


Zoology (rarely spelled zoölogy) is the biological discipline which involves the study of non-human animals. ... Image File history File linksMetadata Download high resolution version (1000x700, 1083 KB) La: Vulpes vulpes. ...

Branches of Zoology

Anthrozoology Anthrozoology is the study of human-animal interaction, also described as the science focusing on all aspects of the human-animal bond. ...


Apiology Apiology is the scientific study of bees, a branch of entomology. ...


Arachnology Arachnology is the scientific study of spiders and related organisms such as scorpions, pseudoscorpions, harvestmen, collectively called arachnids. ...


Cetology Cetology is the branch of marine mammal science that studies the approximately eighty species of whales, dolphins, and porpoise in the scientific order Cetacea. ...


Entomology Not to be confused with Etymology, the study of the origin of words. ...


Ethology This article or section does not adequately cite its references or sources. ...


Herpetology Herpetology (Greek herpeton = to creep, to ramp and logos = in this context explanation or reason) is the branch of zoology concerned with the study of reptiles and amphibians. ...


Ichthyology Ichthyology is the branch of zoology devoted to the study of fish. ...


Mammalogy In zoology, mammalogy is the study of mammals – a class of vertebrates with characteristics such as homeothermic metabolism, fur, four-chambered hearts, and complex nervous systems. ...


Myrmecology It has been suggested that this article or section be merged with List of notable myrmecologists. ...


Neuroethology Neuroethology (from Greek - neuron meaning from nerves, ethos meaning trait or character, and logos meaning words or study) is the scientific study of animal behaviour with its base in neurology. ...


Ornithology Ornithology (from the Greek ornis = bird and logos = word/science) is the branch of zoology concerned with the scientific study of birds. ...


Paleozoology Paleozoology (Greek: paleon = old and zoon = animal) is the branch of paleontology dealing with the recovery and identification of animal remains from archeological (or even geological) contexts, and their use in the reconstruction of past environments and economies. ...


Primatology Primatology is the study of non-human primates. ...

History

pre-Darwin This article considers the history of zoology before the theory of evolution proposed by Charles Darwin in 1859. ... This article considers the history of zoology before the theory of evolution proposed by Charles Darwin in 1859. ...

post-Darwin
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This article considers the history of zoology in the years up to 1912, since the theory of evolution by natural selection proposed by Charles Darwin in 1859. Charles Darwin gave new stimulus and new direction to morphology and physiology, by uniting them as part of a common biological theory: the theory of organic evolution but a part of the wider doctrine of universal evolution based on the laws of physics and chemistry. ... Zoology (rarely spelled zoölogy) is the biological discipline which involves the study of non-human animals. ... This article is about evolution in biology. ... Darwins illustrations of beak variation in the finches of the Galápagos Islands, which hold 13 closely related species that differ most markedly in the shape of their beaks. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... 1859 (MDCCCLIX) is a common year starting on Saturday of the Gregorian calendar (or a common year starting on Monday of the Julian calendar). ...


Charles Darwin gave new direction to morphology and physiology, by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon a genealogical basis, fresh investigation of the development of animals, and early attempts to determine their genetic relationships. For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ... Leonardo da Vincis Vitruvian Man, an important early achievement in the study of physiology. ... Genealogy is the study and tracing of family pedigrees. ...

Contents

Early 20th century work

After publication of the Origin of Species, Darwin became interested in the animal and plant mechanisms that confer advantages to individual members of a species. Much important work was done by Fritz Muller (Für Darwin), by Herman Muller (Fertilization of Plants by Insects), August Weismann, Edward B. Poulton and Abbott Thayer. There was considerable progress during this period in the field that would become known as genetics, the laws of variation and heredity (originally known as thremmatology[citation needed]). The progress of microscopy gave a clearer understanding of the origin of the egg-cell and sperm-cell and the process of fertilization. The 1859 edition of On the Origin of Species First published in 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 British naturalist Charles Darwin is one of the pivotal... August Weismann Friedrich Leopold August Weismann (b. ... For a non-technical introduction to the topic, please see Introduction to genetics. ... Heredity (the adjective is hereditary) is the transfer of characteristics from parent to offspring through their genes, or the transfer of a title, style or social status through the social convention known as inheritance (for example, a Hereditary Title may be passed down according to relevant customs and/or laws). ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ... Different types of sperm cells: A) spermatozoon (motile), B) spermatium (non-motile), C) fertilization tube with sperm nuclei For other uses, see Sperm (disambiguation). ... Categories: Biology stubs ...


Mendel and zoology

Gregor Mendel's experiments on cultivated varieties of plants were published in 1865, but attracted little notice until thirty-five years later, sixteen years after his death (see Mendelism). Mendel tried to gain a better understanding of heredity. His main experiments were with varieties of the edible pea. He chose a variety with one marked structural feature and crossed it with another variety in which that feature was absent. For example, he hybridized a tall variety, with a dwarf variety, a yellow-seeded variety with a green-seeded variety, and a smooth-seeded variety with a wrinkle-seeded variety. In each experiment, he concentrated on one character; after obtaining a first hybrid generation, he allowed the hybrids to self-fertilize, and recorded the number of individuals in the first, second, third, and fourth generations in which the chosen character appeared. Gregor Johann Mendel (July 20, 1822[1] – January 6, 1884) was a Moravian[2] Augustinian priest and scientist often called the father of modern genetics for his study of the inheritance of traits in pea plants. ... Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets that underlie much of genetics developed by Gregor Mendel in the latter part of the 19th century. ... Heredity (the adjective is hereditary) is the transfer of characteristics from parent to offspring through their genes, or the transfer of a title, style or social status through the social convention known as inheritance (for example, a Hereditary Title may be passed down according to relevant customs and/or laws). ... Binomial name Pisum sativum L. A pea is the small, edible round green bean which grows in a pod on the leguminous vine Pisum sativum, or in some cases to the immature pods. ...


In the first hybrid generation, nearly all the individuals had the positive character, but in subsequent generations the positive character was not present in all individuals: half had the character and half did not. Thus the random pairing of two groups of reproductive cells yielded the proportion 1 PP, 2 PN, 1 NN, where P stands for the character and N for its absence - the character was present in three-quarters of the offspring and absent from a quarter. The failure of the character to distribute itself among all of the reproductive cells of a hybrid individual, and the limitation of its distribution to half only of those cells, prevents the swamping of a new character by interbreeding. The tendency of the proportions in the offspring is to give, in a series of generations, a reversion from the hybrid form PN to a race with the positive character and a race without it. This tendency favours the persistence of a new character of large volume suddenly appearing in a stock. The observations of Mendel thus favoured the view that the variations upon which natural selection acts are not small but large and discontinuous. However, it did not appear that large variations would be favoured any more than small ones, or that the eliminating action of natural selection upon an unfavourable variation could be checked.


Much confusion arose in discussions of this topic, because of defective nomenclature. Some authors used the word mutation only for large variations that appeared suddenly and which could be inherited, and fluctuation for small variations, whether they could be transmitted or not. Other authors used fluctuation only for small, acquired variations due to changes in food, moisture and other features of the environment. This kind of variation is not heritable, but the small variations to which Darwin attached importance are. The best classification of the variations in organisms separates those which arise from congenital variations from those which arise from variations of the environment or the food-supply. The former are innate variations, the latter are "acquired variations". Both innate and acquired variations include some which are more and some which are less obvious. There are slight innate variations in every new generation of every species; their greatness or smallness so far as human perception goes is not of much significance, their importance for the origin of new species depends on whether they are valuable to the organism in the struggle for existence and reproduction. An imperceptible physiological difference might be of selective value, and it might carry with it correlated variations which may or may not appeal to the human eye but which are of no selective value themselves.


The views of Hugo de Vries and others about the importance of saltatory variation, the soundness of which was still not generally accepted in 1910, may be gathered from the article Mendelism. A due appreciation of the far-reaching results of correlated variation must, it appeared, give a new and distinct explanation of large mutations, discontinuous variation, and saltatory evolution. The analysis of the specific variations of organic form to determine the nature and limitation of a single character, and whether two variations of a structural unit can blend when one is transmitted by the male parent and the other by the female, were yet to be determined. It was not clear whether absolute blending was possible, or whether all apparent blending was only a more-or-less minutely subdivided mosaic of non-combinable characters of the parents. Hugo Marie de Vries (16th February 1848-21st May 1935), a Dutch biologist, was one of three men - see also Carl Correns and Erich von Tschermak - who in 1900 rediscovered Gregor Mendels work on genetics. ... Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets that underlie much of genetics developed by Gregor Mendel in the latter part of the 19th century. ...


Another important development of Darwin's conclusions deserves notice. The fact of variation was familiar: no two animals, even of the same brood, are alike. Jean-Baptiste Lamarck hypothesised that structural alterations acquired by a parent might be transmitted to the offspring, and as these are acquired by an animal or plant as a consequence of the action of the environment, the offspring would sometimes start with a greater fitness for those conditions than its parents started with. In turn, it would acquire a greater development of the same modification, which it would transmit to its offspring. Lamarck argued that, over several generations, a structural alteration might thus be acquired. The familiar illustration of Lamarck's hypothesis is that of the giraffe, whose long neck might, he suggested, was acquired by the efforts of a short-necked race of herbivores who stretched their necks to reach the foliage of trees in a land where grass was deficient, the effort producing a longer neck of each generation, which was then transmitted to the next. This process is known as 'direct adaptation'. Jean-Baptiste Lamarck. ... Binomial name Giraffa camelopardalis Linnaeus, 1758 Range map The giraffe (Giraffa camelopardalis) is an African even-toed ungulate mammal, the tallest of all land-living animal species. ... A deer and two fawns feeding on some foliage A herbivore is often defined as any organism that eats only plants[1]. By that definition, many fungi, some bacteria, many animals, about 1% of flowering plants and some protists can be considered herbivores. ...


Such structural adaptations are acquired by an animal in the course of its life, but are limited in degree and rare, rather than frequent and obvious. Whether acquired characters could be transmitted to the next generation was a very different issue. Darwin excluded any assumption of the transmission of acquired characters. He pointed to the fact of congenital variation, and showed that congenital variations are arbitrary and non-significant.


Congenital variation

At the beginning of the twentieth century, the causes of congenital variation were obscure, although it was recognised that they were largely due to a mixing of the matter which constituted the fertilized germ or embryo-cell from two individuals. Darwin had shown that congenital variation was all-important. A popular illustration of the difference was this: a man born with four fingers only on his right hand might transmit this peculiarity to at least some of his children; but a man with one finger chopped off will produce children with five fingers. Darwin, influenced by some facts which seemed to favour the Lamarckian hypothesis, thought that acquired characters are sometimes transmitted, but did not consider that this mechanism was likely to be of great importance.


After Darwin's writings, there was an effort to find evidence for the transmission of acquired characters; ultimately, the Lamarckian hypothesis of transmission of acquired characters was not supported by evidence, and was dismissed. August Weismann argued from the structure of the egg-cell and sperm-cell, and from how and when they are derived in the growth of the embryo from the egg, that it was impossible that a change in parental structure could produce a representative change in the germ or sperm-cells. August Weismann Friedrich Leopold August Weismann (b. ...


The only evidence that seemed to support the Lamarckian hypothesis were the experiments of Brown-Séquard, who produced epilepsy in guinea-pigs by bisection of the large nerves or spinal cord, which led him to believe that, in rare instances, the artificially-produced epilepsy and mutilation of the nerves was transmitted. The record of Brown-Séquard's original experiments was unsatisfactory, and attempts reproduce them were unsuccessful. Conversely, the vast number of experiments in the cropping of the tails and ears of domestic animals, as well as of similar operations on man, had negative results. Stories of tailess kittens, puppies, and calves, born from parents one of whom had been thus injured, are abundant, but failed to stand experimental examination. Binomial name Cavia porcellus (Linnaeus, 1758) Guinea pigs (also called cavies) are rodents belonging to the family Caviidae and the genus Cavia, originally indigenous to the Andes. ... The Spinal cord nested in the vertebral column. ...


Whilst evidence of the transmission of an acquired character proved wanting, the a priori arguments in its favour were recognized as flawed, and cases which appeared to favour the Lamarckian assumption were found to be better explained by the Darwinian principle. For example, the occurrence of blind animals in caves and in the deep sea was a fact which even Darwin regarded as best-explained by the atrophy of the eye in successive generations through the absence of light and consequent disuse. However, it was suggested that this is better explained by natural selection acting on congenital fortuitous variations. Some animals are born with distorted or defective eyes. If a number of some species of fish are swept into a cavern, those with perfect eyes would follow the light and eventually escape, leaving behind those with imperfect eyes to breed in the dark place. In every succeeding generation this would be the case, and even those with weak but still seeing eyes would escape, until only a pure race of blind animals would be left in the cavern.


Transmission

It was argued that the elaborate structural adaptations of the nervous system which underlie instincts must have been slowly built up by the transmission to offspring of acquired experience. It seemed hard to understand how complicated instincts could be due to the selection of congenital variations, or be explained except by the transmission of habits acquired by the parent. However, imitation of the parent by the young account for some, and there are cases in which elaborate actions must be due to the natural selection of a fortuitously-developed habit. Such cases are the habits of 'shamming dead' and the combined posturing and colour peculiarities of certain caterpillars (Lepidoptera larvae) which cause them to resemble dead twigs or similar objects. The advantage to the caterpillar is that it escapes (say) a bird which would, were it not deceived, attack and eat it. Preceding generations of caterpillars cannot have acquired this habit of posturing by experience; either a caterpillar postures and escapes, or it does not posture and is eaten - it is not half eaten and allowed to profit by experience. Thus, we seem justified in assuming that there are many movements of stretching and posturing possible to caterpillars, that some had a fortuitous tendency to one position, some to another, and, that among all the variety of habitual movements, one is selected and perpetuated because it happened to make the caterpillar look more like a twig. Superfamilies Butterflies Hesperioidea Papilionoidea Moths Acanthopteroctetoidea Alucitoidea Axioidea Bombycoidea Calliduloidea Choreutoidea Cossoidea Drepanoidea Epermenioidea Eriocranioidea Galacticoidea Gelechioidea Geometroidea Gracillarioidea Hedyloidea Hepialoidea Heterobathmioidea Hyblaeoidea Immoidea Incurvarioidea Lasiocampoidea Lophocoronoidea Micropterigoidea Mimallonoidea Mnesarchaeoidea Neopseustoidea Nepticuloidea Noctuoidea Palaephatoidea Pterophoroidea Pyraloidea Schreckensteinioidea Sesioidea Simaethistoidea Thyridoidea Tineoidea Tischerioidea Tortricoidea Urodoidea Whalleyanoidea Yponomeutoidea Zygaenoidea The order Lepidoptera...


Record of the past

Man, compared with other animals, has the fewest instincts and the largest brain in proportion to body size. He builds up, from birth onwards, his own mental mechanisms, and forms more of them, and takes longer in doing so, than any other animal. The later stages of evolution from ape-like ancestors have consisted in the acquisition of a larger brain and in the education of that brain. A new feature in organic development makes its appearance when we set out the facts of man's evolutionary history. This factor is the record of the past, which grows and develops by laws other than those affecting the perishable bodies of successive generations of mankind, so that man, by the interaction of the record and his educability, is subject to laws of development unlike those by which the rest of the living world is governed.


References

  • This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

 
 

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