It's something that's been long suspected by kids who have siblings and eternally denied by parents who have more than one child: mothers and fathers have a favourite out of their offspring.
"How could you think such a thing?" parents will tell their children. "Of course we don't have a favourite!"
Well, guess what folks, our parents have been lying all along... though they might not have realised it.
A recent study conducted by Rutgers University in New Brunswick found that fathers have a preferential bias towards their sons, while mothers favour their daughters.
The study, titled, 'Sexual conflict and the Trivers-Willard hypothesis: Females prefer daughters and males prefer sons', initially set out to test the 1973 Trivers-Willard hypothesis - a theory that predicted that wealthy parents would invest in sons, but poor parents would invest in daughters.
More than 750 participants were initially given tests to determine whether their wealth status would influence whether they would be more likely to adopt/give money to a charity that supports boys or girls.
It was expected that wealthier parents would support male children and poorer ones would favour female children - but this did not show in the results. Instead, it showed that parents tended to prefer children that were the same gender as them.
Women's preferences for daughters were slightly higher than men's preferences for sons, but the overall bias was still significant enough to reach the conclusion quite easily.
So, what does this mean for the sons of mothers and daughters of fathers? Well, it depends how you look at it.
On the one hand, while people may favour hypothetical children of their own gender, that might not always be true in real life. On the other, if it does translate to real family set-ups, it could mean that kids may find themselves being overlooked by their differently-gendered parents.
What's more, the study points out, because of the increasing rates of single parents (most often mothers) raising children, the next generation of adults could be affected by their parents' gender bias.
"These results may also have implications for rising income inequality and intergenerational social mobility," the study said. "A recent study using the tax records of 40 million Americans between 1996 and 2012 showed that the single best predictor of lower intergenerational social mobility was having a single or divorced parent. Because most of these single parents are females, and females prefer daughters, we might expect even lower reduced intergenerational mobility for the sons of these single mothers."
Even given this information, it's likely that most parents would still argue that they have no bias whatsoever. Mothers will always claim that they love their sons as much as their daughters, and fathers will remain adamant that they do not favour their little boys over their girls.
Whether or not a parent thinks it's true, however, it's still worth keeping in mind so that they do not treat their children differently because of their gender. All kids deserve equal opportunity, no matter who they are.
