274 SCIENCE FROM AN EASY CHAIR 



One result of failure of the germ to " grow up " into 

 the perfect likeness of its parents is that it may " throw 

 back," as the breeders say, and resemble in this or that 

 quality a remote, even an extremely remote, ancestor. 

 It is suggested by some inquirers that the congenital or 

 inborn defect, frequent in human beings, which is called 

 " feeble-mindedness " is a reversion or throw-back to the 

 condition of the brain in the animal ancestors of man. 

 That is possible, and, in view of some cases, seems prob- 

 able. But it must be noted that we do not know what 

 are the causes which favour throwing-back, or " atavism," 

 as it is called, in regard to all sorts of structures, and 

 that the mechanical conditions connected with the growth 

 of the cavity of the skull in which the brain itself grows 

 are so very elaborate that it is obvious that a very slight 

 disturbance of one element or another might arrest or 

 turn aside the growth of that vastly complex organ, which 

 has become so much larger and more delicate in man 

 than in the animals from which he has, at no remote 

 period in the history of life on the earth, taken his origin. 



Mankind have always within the period of written 

 records (a mere trifle in the lapse of time since man 

 became man) regarded mental defect and aberration as 

 due to fantastic causes. To this day we use the word 

 " lunatic " for one of the two typical forms of mental 

 aberration : we imply that the moon is concerned in its 

 production. The other form of brain-failure has appropri- 

 ated the term " idiot," which, it is surprising to find, was 

 less than two centuries ago applied in common speech 

 to any person who was characterised by independence of 

 judgment. The term "softy" is a common and really 

 more suitable term for this class, whilst " cracked " is the 

 word applied to a lunatic. The notion that mental 

 aberration is due to " possession " by evil spirits, which 

 can be expelled and the patient accordingly cured, was 



