764. REPORT—1899, 
only displayed under their influence are what we call acquired characters. They 
are acquired in response to the external stimuli. 
It would appear, then, that every feature which successively appears in an 
organism in the march from the uninucleated zygote to death is an acquired 
character. At first the stimuli which are necessary are quite simple, being little 
more than appropriate heat and moisture; later on they become more complicated, 
until finally, when the developmental period is over and the mature life begins, 
the necessary conditions attain their greatest complexity, and their fulfilment 
constitutes what we call in the higher animals education. Education is nothing 
more than the response of the nearly mature organism to external stimuli, the 
penultimate response of the zygote to external stimuli, the ultimate being those of 
senile decay, which end in natural death. Acquired properties, it will be seen, are 
really stages in the developmental history. They differ in the complexity of the 
stimulus required to bring them out. For instance, the segmentation of the egg 
requires little more than heat and moisture, the walling of the chick the stimulus 
of light and sound and gravity, the evolutions of an acrobat the same in greater 
complexity, and lastly the action of a statesman requires the stimulation of almost 
every sense in the greatest complexity. Moreover, not only are there differences 
in the complexity of the stimulus required, but also in the rapidity with which the 
organism reacts to it. The chick undergoes its whole embryonic development 
in three weeks, a man in nine months; the chick develops its walking mechanism 
in a few minutes, while a man requires twelve months or more to effect 
the same end, Chickens are much cleverer than human beings in this respect. 
There is the same kind of difference between them that there is between 
the power of learning displayed by a Macaulay and that displayed by a stupid 
child. 
An instinct is nothing more than an internal mechanism which is developed 
with great rapidity in response to an appropriate stimulus. It is difficult for us 
to understand instincts, because with us almost all developmental processes are 
extremely slow and gradual. This particularly applies to the development of those 
nervous mechanisms, the working of which we call reason. 
Within certain limits the external conditions may vary without harming the 
organism, but such variations are generally accompanied by variations in the form 
in which the properties of the zygote are displayed. If the variations of the 
conditions are too great, their action upon the organism is injurious, and results in 
abortions or death. And in no case can the external conditions call out properties 
with which the zygote was not endowed at the act of conjugation. 
It would thus appear that acquired characters are merely phases of develop- 
ment; they are the manifestations of the properties of the zygote, and are called 
forth only under appropriate stimulation; moreover, they are capable of varying 
within certain limits, according to the nature of the stimulus, and it is to these 
variations that the term ‘ acquired character’ has been ordinarily applied. 
A genetic character, on the other hand, is the possibility of acquiring a certain 
feature under the influence of a certain stimulus; it is not the feature itself—that 
is an acquired character—but it is the possibility of producing the feature. Now 
as the possibility of producing the feature can only be proved to exist by actually 
producing it, the term ‘genetic character’ is frequently applied to the feature 
itself, which is, as we have seen, an acquired character. In consequence of this 
fact, that we can only determine genetic characters by examining acquired 
characters, a certain amount of confusion may easily arise, and has indeed often 
arisen, in dealing with this subject. This can be avoided by remembering that 
in describing genetic characters account must always be taken of the conditions. 
For example, the white fur of the Arctic hare is an acquired character, acquired in 
response to a certain stimulus; while the power of so responding to the particular 
stimulus when applied at the correct time is a genetic character. Thus a genetic 
character is a character which depends upon the nature of the organism, while an 
acquired character depends on the nature of the stimulus. 
If we imagine a zygote to be a machine capable of working out certain results on 
material supplied to it, then we should properly apply the term ‘genetic character’ 
