2. _The Biological Factor of Prostitution_.--Economic considerations, as we see, have a highly important modificatory influence on prostitution, although it is by no means correct to assert that they form its main cause. There is another question which has exercised many investigators: To what extent are prostitutes predestined to this career by organic constitution? It is generally admitted that economic and other conditions are an exciting cause of prostitution; in how far are those who succumb predisposed by the possession of abnormal personal characteristics? Some inquirers have argued that this predisposition is so marked that prostitution may fairly be regarded as a feminine equivalent for criminality, and that in a family in which the men instinctively turn to crime, the women instinctively turn to prostitution. Others have as strenuously denied this conclusion. Lombroso has more especially advocated the doctrine that prostitution is the vicarious equivalent of criminality. In this he was developing the results reached, in the important study of the Jukes family, by Dugdale, who found that "there where the brothers commit crime, the sisters adopt prostitution;" the fines and imprisonments of the women of the family were not for violations of the right of property, but mainly for offences against public decency. "The psychological as well as anatomical identity of the criminal and the born prostitute," Lombroso and Ferrero concluded, "could not be more complete: both are identical with the moral insane, and therefore, according to the axiom, equal to each other. There is the same lack of moral sense, the same hardness of heart, the same precocious taste for evil, the same indifference to social infamy, the same volatility, love of idleness, and lack of foresight, the same taste for facile pleasures, for the orgy and for alcohol, the same, or almost the same, vanity. Prostitution is only the feminine side of criminality. And so true is it that prostitution and criminality are two analogous, or, so to say, parallel, phenomena, that at their extremes they meet. The prostitute is, therefore, psychologically a criminal: if she commits no offenses it is because her physical weakness, her small intelligence, the facility of acquiring what she wants by more easy methods, dispenses her from the necessity of crime, and on these very grounds prostitution represents the specific form of feminine criminality." The authors add that "prostitution is, in a certain sense, socially useful as an outlet for masculine sexuality and a preventive of crime" (Lombroso and Ferrero, _La Donna Delinquente_, 1893, p. 571).