210 Animal Music, its Nature and Origin. [ April, 
is evident, therefore, that birds acquire their songs as infants 
acquire a language, by instruction rather than by instinct; and 
that those of the same species sing alike for the same reason that 
children of one nationality speak alike, viz: that their instructors 
have a common tongue. 
The next question is, how birds came originally by the notes 
which are peculiar to each species. Daines Barrington answers 
this also, saying substantially that scarcely any two birds of the 
same species sing exactly alike; there are, so to speak, “ provincial 
dialects ” in different districts, as well as individual mannerisms 
and defects. All these minor differences, continually renewed, 
will be imitated by the young birds, and passing from them to 
succeeding generations, will be perpetuated and grow to wider 
divergencies. The loss of a parent at the critical period, also, 
will compel the young bird to invent or copy from other birds, 
perhaps of different species. Had this explanation been thought 
out a hundred years later, in 1873, it would have been added that 
of all these variations sexual selection would perpetuate the 
most agreeable, so that, as Darwin says (11, p. 378), “It is not 
difficult to imagine the steps by which the notes of a bird, pri- 
marily used as a mere call, or for some other, purpose, might 
have been improved into a melodious love song.” 
The ultimate origin of melody is a more difficult problem. 
Darwin writes elsewhere (11, p. 569), “ But if it be further asked 
why musical tones in a certain order and rhythm give man and 
other animals pleasure, we can no more give the reason than for the 
pleasantness of certain tastes and smells.” I will attempt here to 
briefly answer this question, reserving at present the fuller state- 
ment of a theory, which, very strangely, has never before been 
. hit upon, though Darwin in the paragraph preceding that just 
quoted, and Helmholtz (111, p. 553) have almost come upon it, 
and then passed by. 
A musical sound is compound in its structure, being really a 
group of simple tones heard simultaneously; in fact, a chord. 
This group is composed of a ground tone or fundamental, which 
predominates, and of a number of overtones, that decrease in 
intensity as they rise in pitch through a series of harmonic inter- 
vals, Thus between the ground-tone and over-tone No. 1 is the 
interval of an octave; between Nos. 1 and 2, of a fifth; between 
Nos. 2 and 3, of a fourth; between Nos. 3 and ‘4, of a major 
third (see songs No. 1). These intervals, the octave, fifth, fourth 
