4 
INTRODUCTION. 
marck long ago came to this conclusion, which has lately 
been maintained by several eminent naturalists and 
philosophers ; for instance by Wallace, Huxley, Lyell^ 
Yogt, Lubbock, Buchner, Bolle, &c., ] and especially by 
Hackel. This last naturalist, besides his great work, 
6 Generelle Morphologie ’ (1866), has recently (1868, 
with a second edit, in 1870), published his ‘ Naturliche 
Schopfungsgeschichte/ in which he fully discusses the 
genealogy of man. If this work had appeared before 
my essay had been written, I should probably never 
have completed it. Almost all the conclusions at which 
I have arrived I find confirmed by this naturalist, whoso 
knowledge on many points is much fuller than mine. 
Wherever I have added any fact or view from Prof. 
Hackehs writings, I give his authority in the text, other 
statements I leave as they originally stood in my manu- 
script, occasionally giving in the foot-notes references 
to his works, as a confirmation of the more doubtful or 
interesting points. 
During many years it has seemed to me highly pro- 
bable that sexual selection has played an important 
part in differentiating the races of man; but in my 
1 As the works of the first-named authors are so well known, I need 
not give the titles ; but as those of the latter are less well known in 
England, I will give them ‘ Sechs Vorlesungen fiber die Darwin— 
sche Theorie : ’ zweite Auflage, 1868, yon Dr. L. Buchner; translated 
into French under the title ‘ Conferences sur la Theorie Darwinienne,^ 
1869. ‘ Der Mensch, im Lichte der Darwin'sche Lehre/ 1865, von 
Dr. F. Rolle. I will not attempt to give references to all the authors 
who have taken the same side of the question. Thus G. Canestrini 
has published (‘ Annuario della Soc. d. Nat.,’ Modena, 1867, p. 81) a 
very curious paper on rudimentary characters, as bearing on the origin 
of man. Another work has (1869) been published by Dr. Barrago 
Francesco, bearing in Italian the title of “ Man, made in the image of’ 
God, was also made in the image of the ape.” 
