Birth Order, Personality Divergence, and Political Orientation

Key Insight

Sibling personalities diverge significantly, more so than their intelligence or physical traits, as an adaptation to different family niches. This divergence, akin to an evolutionary process, helps siblings avoid direct competition for parental attention, love, and investment. Birth-order expert Frank Sulloway notes that these personality differences are 'Darwinian adaptations for enhancing parental love and attention,' allowing each child to carve out a unique position within the family structure.

First-borns often occupy a preferential niche by identifying with parental authority, core values, and aspirations, typically exhibiting traits like conscientiousness and a drive for achievement. For instance, a first-born might excel in academics. Later-borns, to avoid direct competition with an older sibling's established strengths, tend to diversify their interests, identifying with the other parent or more peripheral family interests. This leads to later-borns having a greater variety of interests and being more open to experience, as evidenced by a 1960s study that found older sons driven by conscience, while younger sons had a 'wide variety of interests.'

These personality traits directly correlate with political orientation: first-borns, being more achievement-oriented and conscientious, often lean politically conservative, while later-borns, who are more open, risk-taking, and rebellious, tend to be more politically liberal. This evolutionary struggle also impacts survival and parental bonding; parents may form stronger bonds with first-borns, and vaccination rates can decrease by 20-30% for each increasing birth rank, irrespective of socio-economic class. Research from the 1970s found children of fifth and higher birth ranks experienced two to three times the usual infant mortality rates, underscoring the profound and lasting impact of birth order on personality and life outcomes.