larger, and more space must be given up to coal, and this diminishes the remaining accommodation.
"Evolution may produce an altogether new type of vessel that shall be more efficient than the old one, but when a particular type has become adapted to its functions, through long experience, it is not possible to produce a mere variety of its type that shall have increased efficiency in some one particular without detriment to the rest. So it is with animals."
This quotation from Galton shows how a type may be established by selection, and it also shows why it is not possible to make any great and permanent change in the type of one characteristic of an organism unless changes at the same time occur in the type of other characters of the same organism. It also follows that a breeder of domesticated animals or cultivated plants who devotes his attention to one characteristic exclusively must soon reach a point where no further improvement in this quality is practicable unless the spceies is at the same time modified in other respects. This fact does not prove that specific stability is due to anything else than selection. It only proves that no great change is possible without the co-ordinated modification of correlated features, and this is just what we should expect as the effect of long ages of selection.
The passage I have quoted from Galton seems to indicate that, after all, he may believe that the specific types of zoölogy and botany are nothing more than the persistent effects of past selection, and that his statement that "organic stability is independent of selection" may refer to present selection only.
These statements are clear and explicit, however, and they have been interpreted by most readers as a flat contradiction of the view that the mechanism which leads to the formation of new types is identical, on its vital side, with that which preserves established types; the view that the differences between the two are differences in the external world.
He says (Nature, September 4, 1885): "It is some years since I made an extensive series of experiments in the produce of seeds of different sizes, but of the same species. . . . It appears from these experiments that the offspring did not tend to resemble their parent seeds in size, but to be always more mediocre than they; to be smaller than they if the parents were large; to be larger than the parents if the parents were very small," and that the analysis of the family records of heights of 205 human parents and 930 children fully confirms and goes far beyond the conclusions obtained from seeds, as it gives with great precision and unexpected coherence the numerical value of the regression toward mediocrity. He says that this regression is a necessary result of the fact that "the child inherits partly from his parents, partly from
