Full siblings are more likely to physically assault and use weapons against one another than half or stepsiblings.
This is the finding of a study by Dr Roxanne Khan, Dr Vanlal Thanzami, and Jennifer Bowling from University of Central Lancashire who will present their research on Friday 27 June, at the British Psychological Society Division of Forensic Psychology annual conference in Glasgow.
Dr Khan explained: "This study focused on the 'Cinderella Effect' that, according to evolutionary theories, suggests that stepchildren are more likely to experience neglect or abuse than those related by blood. We wanted to explore whether this was the case between full, half and unrelated siblings."
A total of 315 siblings (aged 16 to 55 years old) completed questionnaires detailing how much they fought with their siblings and the severity of the violence. The participants provided information on 618 brothers and sisters. They detailed whether they were full, half siblings or unrelated (step, fostered or adopted siblings). Of these 92 were male and 223 female; 456 were full siblings, 123 were half siblings and 39 were unrelated.
The results showed that half and unrelated siblings used less violence with less severity than full siblings. Interestingly in blended families that comprised of both blood-related and unrelated siblings, participants used more violence towards their related (full and half) siblings, including the use of weapons (e.g., threats/use of weapons, such as heavy/sharp objects or knives).
Dr Khan said: "Contrary to what we expected, this study did not support the 'Cinderella Effect' occurring within siblinghood. Sibling relationships are very complex so we expect a number of other factors may have influenced our results. It could be the case that full siblings expect less retaliation for using violence against their blood brothers and sisters, compared to the uncertain revenge of half or unrelated siblings, and this could explain the friction".