An American researcher says manufacturers of infant formula may have to consider making slightly different products for boys and girls.
Katie Hinde, an evolutionary biologist at Harvard University, has presented research to show many monkeys - and potentially some humans - produce produce different breast milk depending on the gender of the child.
Milk for male offspring is higher in fat and protein while daughters get a greater volume of milk.
Dr Hinde told the BBC further research may allow this to be taken into account in infant formulas.
"I think it's important for us to think about better tailoring formula to the developmental needs of infants, and when those needs might be different between boys and girls we should be doing the research to make a better formula."