32 
THE DESCENT OF MAN. 
Part I. 
explanation to assert that they have all been formed on 
the same ideal plan. With respect to development, 
we can clearly understand, on the principle of varia- 
tions supervening at a rather late embryonic period, 
and being inherited at a corresponding period, how it is 
that the embryos of wonderfully different forms should 
still retain, more or less perfectly, the structure of their 
common progenitor. No other explanation has ever 
been given of the marvellous fact that the embryo of a 
man, dog, seal, bat, reptile, &c., can at first hardly be 
distinguished from each other. In order to understand 
the existence of rudimentary organs, we have only to 
suppose that a former progenitor possessed the parts in 
question in a perfect state, and that under changed 
habits of life they became greatly reduced, either from 
simple disuse, or through the natural selection of those 
individuals which were least encumbered with a super- 
fluous part, aided by the other means previously indi- 
cated. 
Thus we can understand how it. has come to pass 
that man and all other vertebrate animals have been 
constructed on the same general model, why they pass 
through the same early stages of development, and why 
they retain certain rudiments in common. Consequently 
we ought frankly to admit their community of descent : 
to take any other view, is to admit that our own struc- 
ture and that of all the animals around us, is a mere 
snare laid to entrap our judgment. This conclusion 
is greatly strengthened, if we look to the members of 
the whole animal series, and consider the evidence de- 
rived from their affinities or classification, their geo- 
graphical distribution and geological succession. It 
is only our natural prejudice, and that arrogance 
which made our forefathers declare that they were 
descended from demi-gods, which leads us to demur to 
