Such offspring have a higher possibility of congenital birth defects see Coefficient of relationship because it increases the proportion of zygotes that are homozygous for deleterious recessive alleles that produce such disorders  see Inbreeding depression. It has been shown that increased levels of sibling conflict are related to higher levels of anxiety and depression in siblings, along with lower levels of self-worth and lower levels of academic competence. Even in cases where there is a high level of sibling conflict if there is also a high level of sibling warmth then social skills and competence remains unaffected. In most places, incest is illegal, regardless of the ages of the two partners. However, as they begin to grow the mother begins regarding her children differently based on their gender. Marriage with paternal cousins is strictly prohibited. Except for the elder brother in this pair sibling conflict is positively correlated with risky behavior, thus sibling conflict may be a risk factor for behavioral problems. Parents and children cf. They have difficulty regulating their negative emotions and may be likely to externalize it as negative behaviour around the newborn. These additional relationships were termed seconds Hebrew: In South Korea, before , anyone with the same last name and clan were prohibited from marriage. In a review of 48 studies on the children parented by cousins, the rate of birth defects was twice that of non-related couples: In the long run, however, because of this increased exposure of deleterious recessive alleles to natural selection , their frequency decreases more rapidly in inbred population, leading to a "healthier" population with fewer deleterious recessive alleles. It can be seen in biological and adoptive families, but also in other situations where children are brought up in close contact, such as the Israeli kibbutz system and the Chinese shim-pua marriage. This study showed that sibling conflict over personal domain were related to lower levels of self-esteem, and sibling conflict over perceived inequalities seem to be more related to depressive symptoms. McHale and her colleague conducted a longitudinal study using middle age children and observed the way in which the parents contributed to stereotypical attitudes in their kids. They may be malleable theorists and believe that they can affect change on situations and people.