First-born children tend to be more intelligent than their later-born siblings. But when a first-born child dies in infancy and the second-born child becomes the oldest child in the family, that second-born child ends up being just as intelligent as the average first-born child (Kristensen & Bjerkedal, 2007). This suggests that first-borns are smarter than their siblings because they experience a different family environment. So if Joe and Nick murdered Paul…um, never mind.
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