Recent Advances in the Study of Heredity. 159 
light as that in which it appears to us now, whilst his scientific 
successors misapprehended it. 
Section XXXIX, “ Of Generation,” of Erasmus Darwin’s Zoo- 
nomia begins with the following words. 1 “ The ingenious Dr. 
Hartley, in his work on man, and some other philosophers have 
been of opinion, that our immortal part acquires during this life 
certain habits of action or of sentiment which become forever 
indissoluble, continuing after death in a future state of existence; 
and add that if these habits are of the malevolent kind, they must 
render their possessor miserable even in Heaven. I would apply 
this ingenious idea to the generation or production of the embryon 
or new animal, which partakes so much of the form and propensities 
of its parent.” 
“ Owing to the imperfection of language the offspring is termed 
a new 2 animal, but is in truth a branch or elongation of the parent, 
since a part of the embryon-animal is, or was, a part of the parent, 
and therefore in strict language, cannot be said to be entirely new 
at the time of its production; and therefore it may retain some of 
the habits of the parent-system. 
“ At the earliest period of its existence the embryon would seem 
to consist of a living filament with certain capabilities of irritation, 
sensation, volition and association, and also with some acquired 
habits or propensities peculiar to the parents; the former of these 
are in common with other animals ; the latter seem to distinguish 
or produce the kind of animal, whether man or quadruped, with the 
similarity of feature or form of the parent.” 
This is a most remarkable prevision of the idea embodied in 
Butler’s doctrine of oneness of personality of individuals in suc¬ 
cessive generations and in Weismann’s doctrine of the continuity of 
the germ-plasm. According to Erasmus Darwin the germ, or living 
filament, starts with the peculiarities which distinguish the organism 
into which it will develop; and the question how those peculiarities 
got there, does not present itself to him as the outstanding difficulty 
as it did to Charles Darwin. 
The causes which brought about the stagnation—nay retro¬ 
gression—in the study of inheritance during the 19th century are 
not easy to disentangle ; it is therefore with some diffidence that I 
make the following suggestions and I do not wish to be understood 
1 London (1794-1796). I am indebted for my acquaintance with 
this passage to Samuel Butler’s “ Evolution, Old and New.” 
2 The italics are Darwin’s ; Butler prints the whole of the second 
paragraph in italics. 
