Breeding human beings selectively to improve the genetic characteristics and for limiting the transmission of hereditary disease to future generations. While a great deal of research needs to be done to increase the effect of current methods of eugenics, there are four basic positive methods currently being used: artificial insemination; "sperm banks"; "heteronomous fertilization"; and arranged marriages. Cloning may be possible in the future. This, and implants, artificial organs, test-tube babies and other medical technology suggests, in addition to breeding, the manufacturing of humans. Preventive eugenic methods are also used: limiting marriages among those with similar genetic problems, limiting marriage among close relatives, and sterilization of people with undesirable characteristics.
The logical outcome of human history and development is for man to create clones of himself.
This is an extremely emotionally charged area, which can result in the loss of the ability to implement its practice.
Selection of the improved human traits is very difficult, both as to divergent values about appropriate human characteristics, and also as to who selects them.
Finally, that pernicious practice must be condemned which closely touches upon the natural right of man to enter matrimony but affects also in a real way the welfare of the offspring. For there are some who over solicitous for the cause of eugenics, not only give salutary counsel for more certainly procuring the strength and health of the future child – which, indeed, is not contrary to right reason – but put eugenics before aims of a higher order, and by public authority wish to prevent from marrying all those whom, even though naturally fit for marriage, they consider, according to the norms and conjectures of their investigations, would, through hereditary transmission, bring forth defective offspring. And more, they wish to legislate to deprive these of that natural faculty by medical action despite their unwillingness; and this they do not propose as an infliction of grave punishment under the authority of the state for a crime committed, not to prevent future crimes by guilty persons, but against every right and good they wish the civil authority to arrogate to itself a power over a faculty which it never had and can never legitimately possess. Although often these individuals are to be dissuaded from entering into matrimony, certainly it is wrong to brand men with the stigma of crime because they contract marriage, on the ground that, despite the fact that they are in every respect capable of matrimony, they will give birth only to defective children, even though they use all care and diligence. (Papal Encyclical, Casti Connubii, 31 December 1930).