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Child Development
Why Are Siblings So Different From One Another?
Several factors may account for siblings' personality differences.
Posted January 3, 2025 Reviewed by Margaret Foley
Key points
- There are both conscious and unconscious factors that account for differences in siblings.
- Difficult physical situations at a child's birth may lead a child to be raised differently than a sibling.
- Parents project onto each child how they want that child to be, and these projections vary.
Most parents report siblings are different, even opposite from their brothers and sisters. This is the case in the parents’ families when they were growing up and in the new families they create as adults.
There are both conscious and unconscious reasons why siblings are so distinct from one another. Sibling differences are influenced by factors inherent in the children, issues inherent in the adult parents, and issues in life circumstances.
Factors in Children
A child may have a difficult birth and stay in an intensive care unit. Parents may react to their fragility and treat them with kid gloves. Children born with physical and cognitive disabilities—autism, missing limbs, cerebral palsy, blindness, or deafness—may be reacted to differently by parents than siblings born before or after the disabled child.
Issues in Parents
Parents can react to and rear siblings differently because of what’s in the parents’ minds. A child may remind them of their own sibling or another relative, either by their looks or even the day or month they were born. A parent may rear a sibling differently because of his/her own childhood emotional traumas.
Unconscious factors in parents can result in raising children differently. In our clinical work, Homer B. Martin and I found that parents emotionally condition their children into one of two distinct personality roles. This happens when parents project onto each child their unconscious desire of how they want each child to be. These are the same projections their parents placed on them when they were young children. If parents want you to turn out differently than a sibling, you will because they will raise you differently. Parents’ projections are powerful in shaping personality, we discovered.
We found that parents emotionally condition each child distinctly but in patterns. A first-born child may be treated as fragile, needing assistance from others and not expected to be independent. We discovered the next sibling born will likely be reared to be very responsible for himself, goal-oriented at tasks, not needy, and conscientious. Then the next sibling will be raised to be either like the first-born or second-born. Most often the pattern repeats in a skipping fashion. The result is some siblings are quite different, even opposites, while some are alike in their personalities. This emotional conditioning skips around in families, alternating most of the time, and accounts for sibling personality distinctions.
Environmental Circumstances
Real-life issues also enter into why siblings are different. These have to do with what is going on in the family before and when each child is born.
There can be household changes that require parents to downsize or move frequently because of jobs or homelessness. Loss of a job or gaining a new job around the time of a child’s birth can affect why siblings turn out differently.
Changes in family finances affect how each child is reared and can explain why siblings turn out differently. Financial hardship or rapid descent into poverty affects parents and how they raise their children. Death of a close family member, loss of one’s spouse, or divorce at a child’s birth all impact how siblings are reared differently.
What an Identical Twin Study Reveals
Ideal studies about why siblings are different from one another can be found in studies of identical twins. Torgersen and Janson examined the impact of 13 family stressors on identical twin pairs between ages 6 and 15. Such stressors included living in one-parent families, family illness, divorce, family conflict, loss of a parent, frequent family moves, and emotional distress in a family member.
The researchers did measurements of personality on the identical twins at age 29. They found that the sharing of more family stressors in childhood and adolescence correlated with more personality differences at age 29. They concluded that such personality differences may play out through influences on adult attachments.
Those who experienced lower stress were more likely to be married and with children when personality was assessed at age 29. Their lives were more stable. Those with higher life stress were more likely to still be single. Environmental circumstances may correlate with personality and coping distinctions even though the genetic composition in twin pairs is the same.
References
Martin, HB & Adams, CBL. (2018). Living on Automatic: How Emotional Conditioning Shapes Our Lives and Relationships, (Praeger) Bloomsbury Publishing.
Torgersen, AM & Janson, H. Why do identical twins differ in personality: Shared environment reconsidered, Twin Research, 5 (1): 44-52, February, 2002.
