84 SECTIONAL ADDRESSES 
and refuses to capitulate to the fear of the Unknown: the vitalist, a 
sadder but not necessarily a wiser type, finds balm in the limitations and 
failures of human effort.’ So far as I have been able to observe, it is by 
no means obvious to note in the writings of Dr. Haldane, Prof. Hill, 
or the Bishop of Birmingham those signs which are usually associated 
with a contemplation of the failures of the human intellect. 
The mechanistic view of life seems to imply that if, at any instant of 
time, we were to know the precise distribution of the matter and energy 
which are present in an organism, we would have a complete under- 
standing of all its properties. In other words, the behaviour of living 
systems can be completely defined in terms of laws which are fundament- 
ally similar to those which describe the behaviour of inanimate systems. 
It is of interest to consider how far this conception is based on the results 
of observation, and how far it rests on a rather indefinite foundation of 
intuitive belief. 
Let us look for a moment at the theory of the evolution of animate 
from inanimate matter. From a biological point of view it seems at 
first sight reasonable—it seems to be the natural conclusion to draw from 
the process of evolution which characterises the world of living organisms 
and the universe as a whole. The theory gives us a comfortable feeling 
of continuity of thought. Let us look at the position from a physical 
point of view. As a physical phenomenon it is undoubtedly possible for 
a living organism to have been evolved spontaneously from inanimate 
matter. It is also possible for a stone to leap spontaneously from the 
surface of the earth. ‘These things are possible, but are they probable ? 
To obtain some estimate of the degree of probability it may be useful to 
consider the phenomena of Brownian movement. As biologists we are 
very familiar with the spontaneous motion of very small particles lying 
in a liquid medium. We believe that each excursion is due to a difference 
in the intensity of molecular bombardment along the axis of movement. 
The smaller the particle, the greater is the chance that a molecule of water 
will hit the particle without a simultaneous encounter from another 
water molecule coming in an opposite direction. Water molecules are 
moving at random, and the direction of collision is one of chance—the 
larger the particle, the greater is the chance of an equal average intensity 
of bombardment from all directions at any given moment. Now since all 
water molecules are free to move in any direction, the actual number of 
molecules moving in a common direction at any given moment will vary 
from moment to moment, and the same is true for the molecules of a 
pebble on the ground. It is possible for all the particles in a suspension 
of Indian ink to move simultaneously in one direction. It is also possible 
for all the molecules of a pebble to perform the same feat—but in view of 
the very large number of other possibilities, the probability of simultaneous 
co-ordinated movement is very, very small unless we are dealing with 
very small numbers of molecules. The degree of smallness can be judged 
by putting ten black and ten white balls into a box and drawing them 
out at random in lots of ten. The probability that we will draw ten 
white or ten black balls is five times in one million. If we increase 
the numbers and draw one hundred balls, the probability of drawing 
balls all of one colour is so small that we say that anybody who 
