Furthermore, concern about human cloning has diminished because, among other reasons, hundreds of sheep embryos had to be sacrificed to achieve just one successful try. Moreover, the excitement about the possibility to produce human clones and the speculations about whether the clones, besides physical likeness would also inherit similar personalities made us forget that nature does produce identical twins sometimes. It happens that a naturally fertilized cell may produce two identical embryos, occasionally more than two. The University of Minnesota has a department to follow up on the development of natural clones and keeps in contact with dozens such cases. They have found that intellectually, the likeness tends to vanish regardless of the environment in which identical twins grow up.
Inheritance amounts to more than half the characteristic personality traits.
That is why eugenical improvement of the human race through parental selection has proved so difficult. Although it is seldom spoken about, nearly all societies protect themselves against population degeneration. In the United States , compulsory sterilization was legal in certain cases until 1973 . European countries are less idealistic in that aspect. Eugenics exists there and is practiced.