ORGANIC EVOLUTION—-MACNAMARA. 365 
by intelligent thought, while other classes of beings, derived from the 
same forms of matter, have failed to develop these powers, their 
movements being governed by automatic and reflex processes. In 
attempting to give a reason for this state of affairs, we assume that 
at a certain stage of our earth’s formation an aggregation of elements 
came into existence such as that to which we have above referred.1 
Our object is, if possible, to ascertain under what conditions and 
demonstratable properties, this organic matter has developed into 
the orders of animals and plants now living in the world. 
In attempting to master the complex mass of phenomena which 
are involved in the solution of a problem of this kind, there is only 
one rational course to pursue in order to get a view of its cause; we 
must invent an hypothesis—that is, we must place before ourselves 
some more or less likely supposition respecting the cause; and, 
having framed our hypothesis, we must endeavor, on the one hand, 
to prove that the supposed cause exists in nature, that it is com- 
petent to account for the phenomena, and that no other known 
cause is competent to account for them.? 
Various hypotheses have from time to time been promulgated to 
account for the natural evolution of animals and plants. Of these 
theories two at present occupy the serious attention of biologists. 
The one known as Darwin’s hypothesis, or natural selection, assumes 
the progressive evolution of the simpler into more complex orders 
of beings. The other is De Vries’s hypothesis of mutation, which 
assumes that new species of animals and plants have suddenly been 
produced from preexisting fully formed beings.* 
We may best appreciate Darwin’s hypothesis by referring to his 
own remarks on the subject. He states that in his opinion “animals 
have descended from at most only four or five progenitors, and plants 
from an equal or lesser number. This would lead us one step further, 
namely, to the belief that all animals and plants have descended 
from some one prototype.’ * We may suppose that the primeval 
prototype began by producing beings like itself, or so slightly affected 
by external influences as at first to be scarcely distinguishable from 
their parent. When the progeny multiplied and diverged, they came 
more and more under the influence of ‘‘natural selection,’’ and thus 
through countless generations under the operation of this law human 
beings were finally developed. 
Darwin refers to the multitude of the individuals of every species, 
which from one or another cause perish either before or soon after 
attaining maturity. He states that in consequence of the struggle 
1 Evolution Darwinian and Spencerian. The Herbert Spencer Lecture, by Raphael Meldola, F. R.S., 
p. 20. Also Human Speech, by N. C. Macnamara, p. 12, 
3 Huxley’s Essays. Phenomena of the Origin of Matter. Everyman’s Library, Edition, p. 247. 
3 Species and Varieties: their Origin by Mutation, Heredity, and Evolution. By Hugo de Vries. 
4 Origin of Species, p. 484. 
