National life from the standpoint of science / by Karl Pearson.
- Pearson, Karl, 1857-1936.
- Date:
- 1905
Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Credit: National life from the standpoint of science / by Karl Pearson. Source: Wellcome Collection.
103/114 (page 99)
![Heredity and Conduct 99 largely from the unhealthy, the mentally defective, the stupid and unconscientious members of a society, your society will de¬ generate, and that more rapidly than is generally recognised. Thus 25 per cent, of married couples produce 50 per cent, of the next generation. In other words, owing to difference in the size of families, probably about one-sixth of the adult men and women in the community produce more than half the next generation. If that one-sixth chances to be the less thrifty, less conscientious, less sane and less able portion of the community, a very few generations will suffice to totally change the character of a nation. The inex¬ plicable decline and fall of nations following from no apparent external cause receives instant light from the relative fertility of the fitter and unfitter elements combined with what we now know of the laws of inheritance. The one safeguard against this multipli¬ cation of the unfit lies in a selective death- rate. And man as much as any other form of life is subject to natural selection. [This was illustrated by diagrams of the ' Inheritance of Duration of Life,' and of the relation between ' Number of Offspring and Length of Life also by tables giving determinations of the selective death-rate in man.] The effects of natural selection are in man, however, interfered with by other causes, the chief of which is the relative fertility of class. 7—2](https://iiif.wellcomecollection.org/image/b18021785_0104.JP2/full/800%2C/0/default.jpg)
