Aims: To see if social aggression could be caused by genes or the environment, see if social aggression is shared the same cause as physical aggression, if one type of aggression leads to another.
Social aggression: Socially manipulative e.g ignoring others, spreading rumours or making threats to withdraw friendship. (Overtly or covertly expressed)
Procedure: Ppts from Quebec Newborn twin study & all pairs of twins born between Nov 1995 – July 1998. 234 twin pairs had all data of all stages gathered (322 pairs tested but not do all stages)(44 pairs MZ male, 50 MZ female, 41 DZ male, 32 DZ female, 67 mixed sex DZ)
Data gathered longitudinally at 5, 18, 30, 48 & 60 months & again at 6 yrs. 6 yrs, the final data set, researchers focused on. Two rating of each twin’s behaviour – 1 by teacher 1 by classmate. Done at spring term to ensure twins were well known before rating.
Teacher ratings on bases of agreements with series of statements from preschool social behaviour scale & direct & indirect aggression scales. E.g extent does the child make others dislike a child (social aggression) extend does the child get into fights (physical). (3-point likert 0-never 2- often)
Peer rating by each child in twins class having booklet of photos & asked to circle ones that matched 4 different behaviours to do with social aggression (telling others not to play with child) & physical aggression (starting fights)
Results: Higher correlation between ratings of MZ twin pair on physical aggression than same sex DZ twins. Case for both peer & teacher ratings.
Social aggression equally correlated for MZ & DZ twins
Mz share gene for aggression making biologically inherited
Social aggression comes from the environment which they all share so equally correlated.
Conclusion: Strong genetic component to physical aggression but not social aggression which means likely due to environmental effects.
Children who physically aggressive also more likely to display social aggression due to interaction between genes & environment.
As children grow they tend to become more socially aggressive due to social conventions on physical violence & develop different ways to express themselves.
| Strength | Weaknesses |
| A – if social aggression is due to environmental factors might be possible to challenge social aggression & reduce it in young children – changing enviro make others act more friendly, superordinate goal.
V – Measures of twins aggressive behaviour came from two sources both Teacher & class mates – help highlight or eliminate bias making data more valid but they were in good agreement. R – standardized checklist of social & visual aggression for teacher & class mates to pick. (preschool social behaviour & direct & indirect aggression) – easier to replicate for consistencies E – correlation (not manipulating anything) no psychological discomfort for ppts or parents. |
G – Uses small sample size when looking at different groups being compared (44 male MZ, 32 female DZ) – low generalizability as low rep to entire population.
G – Studied age group of 6 – may not be representative of aggression in natural behaviour as young children can’t express it any other way. R – Many EV that researcher is unable to control due to longitudinal study – replication near impossible to test for consistencies. V – Judged as MZ or DZ through visual checks only few DNA tested – some not correctly identified making invalid comparisons. |