390 
GENERAL SUMMARY 
Part II. 
heart) imperfectly developed. This animal seems to 
have been more like the larvae of our existing marine 
Ascidians than any other known form. 
The greatest difficulty which presents itself, when 
we are driven to the above conclusion on the origin of 
man, is the high standard of intellectual power and of 
moral disposition which he has attained. But every one 
who admits the general principle of evolution, must see 
that the mental powers of the higher animals, which 
are the same in kind with those of mankind, though 
so different in degree, are capable of advancement. 
Thus the interval between the mental powers of one 
of the higher apes and of a fish, or between those 
of an ant and scale-insect, is immense. The develop- 
ment of these powers hi animals does not offer any 
special difficulty; for with our domesticated animals, 
the mental faculties are certainly variable, and the 
variations are inherited. No one doubts that these 
faculties are of the utmost importance to animals in a 
state of nature. Therefore the conditions are favour- 
able for their development through natural selection. 
The same conclusion may be extended to man; the 
intellect must have been all-important to him, even at 
a very remote period, enabling him to use language, to 
invent and make weapons, tools, traps, &c. ; bv which 
means, in combination with his social habits, he long 
ago became the most dominant of all living creatures. 
A great stride in the development of the intellect 
will have followed, as soon as, through a previous consi- 
derable advance, the half-art and half-instinct of lan- 
guage came into use ; for the continued use of language 
will have reacted on the brain, and produced an in- 
herited effect ; and this again will have reacted on the 
improvement of language. The large size of the brain 
