May, 1891. 
ANIMAL PEDIGREES. 
103 
On the present occasion, it is not with the whole 
evidence, but with one special side of it, that we shall be con¬ 
cerned, that, namely, which is derived from a study of the 
development of existing animals. Everyone knows that 
animals in the earlier stages of their existence differ greatly 
in form, in structure, and in habits from the adult condition; 
a lung-breathing frog, for example, commencing its life as a 
gill-breathing tadpole ; and a butterfly passing its infancy and 
youth as a caterpillar. It is clear that these developmental 
stages, and the order of their occurrence, can be no mere 
accidents ; for all the individuals of any particular species of 
frog, or of butterfly, pass through the same series of 
changes. It is not, however, until recent vears that 
naturalists have realised that each animal is constrained to 
develop along definitely determined lines; and that the 
successive stages in its life history are forced on an animal in 
accordance with a law, the determination of which ranks as 
one of the greatest achievements of biological science. 
The doctrine of descent, or of Evolution, teaches us that 
as individual animals arise, not spontaneously, but by direct 
descent from pre-existing animals, so also is it with species, 
with families, and with larger groups of animals, and so also 
has it been for all time ; that as the animals of succeeding 
generations are related together, so also are those of succes¬ 
sive geologic periods; that all animals, living or that have 
lived, are united together by blood relationship of varying 
nearness or remoteness ; and that every animal now in 
existence has a pedigree stretching back, not merely for ten 
or a hundred generations, but through all geologic time since 
the dawn of life on this globe. 
The study of Development, in its turn, has revealed to us 
that each animal bears the mark of its ancestry, and is com¬ 
pelled to discover its parentage in its own development; that 
the phases through which an animal passes in its progress 
from the egg to the adult are no accidental freaks, no mere 
matters of developmental convenience, but represent more or 
less closely, in more or less modified manner, the successive 
ancestral stages through which the present condition has been 
acquired. 
Evolution tells us that each animal has had a pedigree in 
the past. Embryology reveals to us this ancestry, because 
every animal in its own development repeats its history, 
climbs up its own genealogical tree. 
Such is the Recapitulation Theory, hinted at by Agassiz, 
and suggested more directly in the writings of Von Baer, but 
first clearly enunciated by Fritz Muller, and since elaborated 
by many, notably by Balfour and Ernst Haeckel. 
