“Civilization is a progress from an indefinite, incoherent homogeneity toward a definite, coherent heterogeneity.”

-Herbert Spencer

A study published in the European Journal of Personality found that birth order has no significant impact on the intelligence, educational attainment, risk aversion, and the big five personality traits within an Indonesian sample. 

This study was conducted by Laura J. Botzet, a psychology researcher at the Department for Biological Personality Psychology at the University of Goettingern; Julia M. Rohrera, a personality psychologist, and Ruben C. Arslan, an evolutionary personality psychologist, both of whom work at the Max Planck Institute for Human Development. 

The intentions behind this study was to explore the trends of birth order effects in diverse societies that are not western, educated, industrialized, rich and democratic (WEIRD). Indonesia is known as a poorer country with bigger families causing fewer resources to be distributed amongst more offsprings.  The hope was to find linear birth order effects as a result of factors like resource dilution. 

The resource dilution theory focuses on the idea that parental resources are increasingly spread thin with every subsequent child as the same capital must be shared amongst more children. Some initial thoughts were that the first child would enjoy these resources for a longer amount of time; as well, the first-borns get to interact with parental figures more often. For these reasons, they are also thought to be more intelligent, neurotic, intellectually open, conscientious, and extraverted in a dominant sense. 

The predictions for this research in alignment with results from WEIRD samples, is that intelligence, intellect, and educational attainment decrease with higher birth order whilst risk aversion, agreeableness, extraversion, neuroticism, and conscientiousness go unaffected.

To test these predictions, 11188 participants were surveyed using the Indonesian Family Life Survey, a longitudinal study. The families were carefully controlled to account for accuracy of birth order effects. 

The intelligence subsurvey required participants aged 15 and older to take part in five tests. First, participants were given a shortened version of the Raven’s matrices test, which was designed to measure abstract reasoning. 

Next, participants took a delayed word recall test which required them to count backwards from 100 in steps of 7 seconds. In the third test, participants read a list of 10 nouns and had to recall as many nouns as possible 4-5 minutes later. Following this, participants took an adaptive number series test where they were shown a pattern of numbers (e.g. 7-8-?-10) and had to guess the missing number. Lastly, participants were administered a math test containing five multiple choice questions. 

The participants personality traits were also measured using the Big Five Index 15. They were then assessed for risk aversion using a hypothetical lottery choice task. 

The results showed that intelligence, risk aversion, openness, neuroticism, extraversion, agreeableness, nor conscientiousness were affected by birth order. In terms of educational attainment, a mild but insignificant association was detected between higher birth order and higher educational attainment. 

The inconsistencies between the findings, hypotheses, and trends seen in WEIRD countries suggest that birth order does not serve as an ideal predictor of life outcomes. 

In conclusion, the study showcases the need to search beyond a WEIRD sample to understand whether certain theories actually do apply universally, or if there are culturally-specific differences.