May, 1891. 
ANIMAL PEDIGREES. 
99 
expresses facts, and facts only, andean never be disturbed. It 
matters not what the occupations or residences of the three 
may be ; they may never see one another ; never even sus¬ 
pect one another's existence. It makes no difference how 
many people may be living contemporaneously, how many 
may have preceded, how many may be born in after ages ; 
this little bit of history remains untouched and absolutely 
true for all time. It is for this reason that genealogy or 
blood relationship affords the only satisfactory basis for a 
classification of men ; and we shall find that the same con¬ 
siderations apply to the lower animals as well. 
One further matter of a preliminary nature requires 
mention. It is customary in preparing genealogical tables to 
construct them as is done above, starting from some one more 
or less remote ancestor, and following upwards the branches 
representing his descendants, so that the whole diagram takes 
the form of an upright tree. It should be noted, however, that 
in a certain sense the diagram would be more correct if it 
were inverted. In tracing back human pedigrees there is a 
marked tendency to follow out one special line of descent, 
and to concentrate attention on one particular ancestor from 
whom we desire to make our line arise, ignoring the fact that 
there were many other contemporary ancestors, from any of 
whom our path might with equal truth have commenced. 
A man has two parents, four grandparents, eight great- 
grandparents ; i.e., in tracing back his pedigree from the 
present time the number of his ancestors in each generation 
is double those of the generation that succeeded it in time. 
This is graphically expressed in the following diagram :— 
M. 
