CHAPTER IX 



STATISTICAL STUDY OF INHERITANCE 



" L'hybride est une mosaique vivante." — Naudin, 



The law of frequency of error " would have been personified by the 

 Greeks, and deified if they had known of it." — Francis Galton. 



§ I. Statistical and Physiological Inquiries. 



§ 2. Historical Note. 



§ 3. ^ Hint of the Statistical Mode of Procedure. 



§ 4. Filial Regression. 



§ 5. Law of Ancestral Inheritance. 



§ 6. Illustration of Results reached hy Statistical Study, 



§ 7. Application to Individual Cases. 



§ 8. Statistical and Physiological Laws. 



§ I. Statistical and Physiological Inquiries 



When we study complex phenomena, such as the weather, we 

 usually follow two methods. On the one hand, we may collect 

 a multitude of observations — e.g., as to the rainfall in different 

 localities and at different times of year, — and try from a careful 

 scrutiny of these to make some general induction, which will 

 show the inherent orderliness of sequences, even in such an 

 apparently disorderly complex as the weather. On the other 

 hand, we may give our attention to the actual mechanism of 

 certain occurrences — e.g., heavy rain with westerly winds and 

 low barometric pressure — and seek to show how certain con- 

 ditions are necessarily followed by certain results. In so doing, 

 we fall back on the general laws of physics, and we may be 



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