George Dvorsky reviews the hotly contested body of research on the effect of birth order on our personalities:
One particularly controversial area of birth order studies is the ongoing debate about intelligence. Firstborns consistently rank higher on intelligence tests.
The going theory is that they get more attention and resources from parents. Indeed, Robert Zajonc says that firstborn children are almost exclusively exposed to adult language, whereas laterborn children experience the less mature, childish speech of their older siblings. This may subsequently explain why firstborns tend to score higher on tests of verbal ability. As for non-firstborns, their older sibling(s) frequently assume the role of parents, answering their questions and offering perspectives, albeit less capably.
Birth order may also have a bearing on our sexuality:
[P]sychologists found that we’re more likely to form long-term platonic and romantic relationships with other people of the same birth order — an effect the researchers say cannot be explained by other factors, such as family size. Studies have also shown that sexual orientation correlates with a man’s number of older brothers. And in fact, each additional older brother increases the odds of homosexuality by about 33%.
(Photo via Awkward Family Photos)