Occasionally, unusual circumstances arise which allow developmental psychologists to investigate phenomena that would be impossible under any other circumstances. For example, the case study of Czech twins studied by Koluchova (1972) allowed researchers to study the effects of severe privation and the Genie case study Curtiss (1977) tested the critical period hypothesis for language development. Such studies are useful as it only takes one case to refute a theory. This is why researchers were so keen to demonstrate that Genie would learn to speak once exposed to a language as this would lead to a career-defining breakthrough in the study language development. For this reason and many others, such studies raise many ethical issues. The children are extremely vulnerable (for more on Ethics, see below) and therefore a psychologist’s first priority must be the young person’s wellbeing. However, stories such as Genie’s demonstrate that sometimes boundaries can become blurred between carer and researcher, leading to damaging outcomes for the child and for the reputation of the psychologists involved.