Chapter XI. Geographical Distribution
The main topics in this chapter are the distribution of land masses, the single centers of creation, and the geological and ice ages.
Darwin’s argument says that the evolution of animals and plants owes more to the pattern of land masses than it does to the climatic conditions in their respective areas. One fact that Darwin uses to support this is the great concentration of dry land in the northern hemisphere (around 70%).
Darwin’s doctrine of single centers of creation is that a species is a unique production of nature happening in a localized region of space and time and which, if it vanishes, will not occur again. One difficulty that arises from this is that one must be able to explain how a single original population spread out to isolated areas, as can be seen with many species.
To understand Darwin’s explanation using ice ages, he focused on the two most recent epochs.
1. The Pliocene (5 million years ago)
2. The Pleistocene (2 million years ago; a period of repeated glaciations or ice ages.)
Ice ages, says Darwin, made the surface of the Earth very different from how it is now, so one is able to localize a single original population and see how it separated when the ice ages progressed, changing the surface of the planet and thus separating that given population.
Darwin’s argument says that the evolution of animals and plants owes more to the pattern of land masses than it does to the climatic conditions in their respective areas. One fact that Darwin uses to support this is the great concentration of dry land in the northern hemisphere (around 70%).
Darwin’s doctrine of single centers of creation is that a species is a unique production of nature happening in a localized region of space and time and which, if it vanishes, will not occur again. One difficulty that arises from this is that one must be able to explain how a single original population spread out to isolated areas, as can be seen with many species.
To understand Darwin’s explanation using ice ages, he focused on the two most recent epochs.
1. The Pliocene (5 million years ago)
2. The Pleistocene (2 million years ago; a period of repeated glaciations or ice ages.)
Ice ages, says Darwin, made the surface of the Earth very different from how it is now, so one is able to localize a single original population and see how it separated when the ice ages progressed, changing the surface of the planet and thus separating that given population.
Chapter XIV. Recapitulation and Conclusion
This final chapter is about Darwin’s predictions on the development of the study of living things now that his theory of evolution is out. He foresees a radical change, and thus something difficult to accept by the naturalists.
One difficulty he finds or leaves the answer open is that living things on earth had a single beginning. Darwin leaves open the possibility that large classes may have emerged through principles other than natural selection.
“When the views entertained in this volume on the origin of species, or when analogous views are generally admitted, we can dimly foresee that there will be a considerable revolution in natural history.” (page 101)
“A grand and almost untrodden field of inquiry will be opened, on the causes and laws of variation, on correlation of growth, on the effects of use and disuse, on the direct action of external conditions, and so forth.” (page 102)
“In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.” (page 104)
“It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” (page 104-105)
One difficulty he finds or leaves the answer open is that living things on earth had a single beginning. Darwin leaves open the possibility that large classes may have emerged through principles other than natural selection.
“When the views entertained in this volume on the origin of species, or when analogous views are generally admitted, we can dimly foresee that there will be a considerable revolution in natural history.” (page 101)
“A grand and almost untrodden field of inquiry will be opened, on the causes and laws of variation, on correlation of growth, on the effects of use and disuse, on the direct action of external conditions, and so forth.” (page 102)
“In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.” (page 104)
“It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” (page 104-105)