Out of Stock
Overview
Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: LECTURE III THE DARWINIAN THEORY (continued) Natural selection?Variation?Struggle for existence?Geometric ratio of rate of increase?Normal number and ratio of elimination in a species?Accidental causes of extinction?Dependence of the strength of a species on enemies?Struggle for existence between individuals of the same species?Natural selection affects all organs and stages?Summary. In artificial selection, through which, with or without conscious intention, our domesticated animals and cultivated plants have arisen, there must obviously be three kinds of co-operative factors: first, the variability of the species; second, the capacity of the organism for transmitting its particular characters to its progeny; and third, the breeder who selects particular qualities for breeding. No one of the factors can be dispensed with; the breeder could effect nothing, were there not presented to him the variations of parts in the particular direction in which he wishes them to vary; an indefinite variation, that is, a variation not guided by selection, would never lead to the formation of new breeds; the species would probably become in time a motley mixture of all sorts of variations, but a breed with definite characters, transmissible in their purity to its descendants, could never be formed. Finally, every process of selective breeding would be futile, if the variations which appeared could not be transmitted. Darwin assumes that processes of transformation quite similar to those which take place under the guidance of Man occur also in nature, and that it is mainly these which have brought about and guided the transformations of species which have taken place in the course of the earth's history. This process he calls natural selection. It will readily be admitted that two out...
| ISBN-13 | 9780217292979 |
|---|---|
| ISBN-10 | 0217292976 |
| Weight | 1.25 Pounds |
| Dimensions | 9.00 x 6.00 x 0.86 In |
| List Price | $25.69 |
| Format | Paperback |
|---|---|
| Pages | 388 pages |
| Publisher | |
| Published On | 2009-08-01 |
View All Offers
Sort by:
Price
