value is exactly that which genealogy ordinarily does not furnish. Dates of birth, death and marriage of an ancestor are of interest, but of limited biological importance. The facts about that ancestor which vitally concern his living descendant are the facts of his character, physical and mental; and these facts are given in very few genealogies.
Fig. 40.—In some pedigrees, particularly those dealing with antiquity, the only part known is the line of ascent which carries the family name,—what animal breeders call the tail-male. In such cases it is evident that from the point of view of a geneticist practically nothing is known. How insignificant any single line of ascent is, by comparison with the whole ancestry, even for a few generations, is graphically shown by the above chart. It is assumed in this chart that no cousin marriages took place.
(b) Genealogies are commonly too incomplete to be of real value. Sometimes they deal only with the