Heredity and Development Second Edition (1972) / Chapter Skim
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1 Darwin's Theory of Pangenesis
1 Darwin's Theory of Pangenesis
Pages 7-18
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From page 7... ...
. With the passage of time the original population would change, its individuals gradually becoming larger, or developing longer legs or a thicker coat of fur, or whatever characteristic was of value for survival.
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From page 8... ...
He attempted, therefore, to assemble data and ideas from individuals who had speculated about inheritance and those who had been concerned with the practical aspects of animal and plant breeding. He added some observations of his own, thought deeply about the problems, and developed the first comprehensive theory of heredity, or as we now call it, genetics.
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From page 9... ...
Another instance was found in some domestic pigs, entirely lacking hind legs, whose abnormality was carried through three generations. To some biologists of the mid-nineteenth century, such instances seemed to be the result of mere chance, or of environmental influence, 1–1 The hand of the porcupine man.
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From page 10... ...
When we reflect that certain extraordinary peculiarities have thus appeared in a single individual out of many millions, all exposed in the same country to the same general conditions of life, and again, that the same extraordinary peculiar ity has sometimes appeared in individuals living under widely different condi tions of life, we are driven to conclude that such peculiarities are not directly due to the action of the surrounding conditions, but to unknown laws acting on the organisation or constitution of the individual; -- that their production stands in hardly closer relation to the conditions than does life itself. If this be so, and the occurrence of the same unusual character in the child and parent cannot be attributed to both having been exposed to the same unusual conditions, then the following problem is worth consideration, as showing that the result cannot be due, as some authors have supposed, to mere coincidence, but must be conse quent on the members of the same family inheriting something in common in their constitution.
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From page 11... ...
Children occasionally resem ble their grandparents or more distant ancestors more closely than they do their parents. Domestic animals may have peculiar features not char acteristic of their breed, but resembling the wild species from which the domestic forms were derived.
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From page 12... ...
If two organisms are crossed and their off spring bred with each other generation after generation, we speak of this as inbreeding. The data available to Darwin suggested that inbreeding would result in a relatively homogeneous population in which there is a blending of characteristics.
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From page 13... ...
The ability to regenerate lost parts is of widespread occurrence and appears to be simi lar to events occurring in embryonic development. Darwin felt that both the formation of a structure during the course of normal development and its replacement following injury to the adult were due to the work ings of inheritance.
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From page 14... ...
During development they unite with partially formed cells or with other gemmules, and in this way produce new cells of the type from which they were formed. We should think of a liver cell as producing gemmules for every part of that cell, enough kinds to produce the identical cell type in the next generation.
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From page 15... ...
Sex. Both sexes transmit inherited characters with equal facility, since both transmit gemmules representing every cell of the body.
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From page 16... ...
In those peculiar cases where the male gametes were thought to have a lasting effect on the reproductive organs of the females (as in Lord Morton's mare) a ready explanation was pos sible.
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From page 17... ...
This sister discipline came to be called genetics. Suggested Readings Charles Darwin was only one of many early workers interested in inheritance.
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From page 18... ...
New York: Schocken Books. The breadth of approach makes this book especially appealing to non-science students.
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