Birth Order

Like any other human study, birth order research presents scientists, psychologists and other researchers with opportunities that unlock more secrets about the human birth order and personality, birth order and intelligence, birth order and health, birth order and sexual orientation and other social factors. As we will soon see, some researchers find significant correlations, say, among first-born children across families. Others find correlations and also non-correlations when studying the various positions of children in a family.
Birth Order Studies
One important variable in studying birth order is the way independent studies are set up. Most researchers conduct in-family and between-family studies, to achieve the greatest degree of correlation possible. Others take a singular approach, studying either in-family or between-family birth order, but not both.
Of particular importance to researchers is the influence and effect of an older sibling on a younger one. This takes into account the older sibling's effect on the younger sibling's intellectual growth, as well as birth order and personality and other traits. Learning more about these and other characteristics provide vital markers for researchers to shape counseling recommendations and also to provide a baseline for further such studies.
Birth Order and Intelligence
Studying birth order and intelligence as a function of birth order traces its roots back to 1874, when Sir Francis Galton - an anthropologist and the founder of the science of eugenics - published a paper on heredity and intelligence. It was the first of several Galton published on the Birth Order, which also included "Inquiries into Human Faculty," "Natural Inheritance," and "Finger Prints".
Galt's ground breaking work paved the way for hundreds of other researchers to delve into this area. It also has led to numerous disagreements among researchers, whose findings often contradict each other and lead to contentious arguments among the experts.