Marian Vidal-Fernandez, University of Sydney and Ana Nuevo-Chiquero, University of Edinburgh
The title of this article might trigger self-satisfied smiles among first-borns, and some concerns among the rest of us.
Many studies show children born earlier in the family enjoy better wages and more education, but until now we didn’t really know why.
Our recently published findings are the first to suggest advantages of first born siblings start very early in life – around zero to three years old! We observe parents changing their behaviour as new children are born, and offering less cognitive stimulation to children of higher birth order.
The birth order puzzle
It now seems clear that for those born and raised in high-income countries such as the United States, the UK and Norway, earlier-born children enjoy higher wages and education as adults – known as the “birth order effect”. Comparing two siblings, the greater the difference in their birth order, the greater the relative benefit to the older child.
However, to date we’ve had no evidence that explains where such differences come from.
We know it’s not an effect of family size, because the effect remains when comparing siblings within the same family and families with the same number of children.
While it makes sense that parents earn more money and gain experience as they get older and have more children, they also need to divide their economic resources and attention among any children that arrive after the first born. We wondered where in childhood these differences began, and what the cause or causes might be.
The origins of the birth order effect
We investigated when birth order differences appear and how they evolve from birth to adolescence. The study involved a longitudinal analysis of around 5,000 American children.