The age of the parent plays a part in degeneracy. Conger[127] (whose results have been corroborated by Joseph Workman, of Toronto, and Kiernan,[128] of Chicago) points out that in all degenerative forms we must take into consideration this factor, since it determines the development of degeneracy in childhood. Hereditary taint may be transmitted to descendants as a simple neuropathy, as a neurosis, or as a defect of development reaching even to idiocy. Conger finds the prevailing age, especially the age of the mothers of degenerates, is often between twenty and twenty-five years, and that hence there exists a relation between this age and the greater transmission of degeneracy to the offspring. Marro, who has specially investigated the influence of the age of the parents, both in the normal population and among criminals,[129] finds that among all classes of criminals there is an excess of immature parents (under 26) or senile parents (over 40), and that only petty offenders possessed a normal number of mature parents (26 to 40 years). A man between 20 and 25 is in as favourable condition for procreating degenerates as the very aged. Because of incompleted organic development he has been unable to free himself from hereditary taint which he transmits to his descendants, but which in maturer age, through the influence of adaptation, evolution, or education, might perhaps be more or less notably modified. The organism between 20 and 25 is yet incomplete; education has not been able to exert much influence in determining those possible changes which are adapted to modify congenital tendencies. In a word, the individual between 20 and 25 feels too much the influence of atavic characters, and too readily transmits to his posterity the brands of degeneracy. Experience has made it well known that the children of the aged readily show degenerate types. Many children of old fathers have undoubtedly inherited all the characters of the weakness of the age in which they were begotten. Old age represents the period of retrogression, of involution, and hence readily transmits the mark of degeneracy. The children of either too young or too old parents, failing to escape hereditary predisposition, may from birth inherit those characters which are proper to incomplete organic development or to the period of involution.