Researchers from Newcastle University note that those men, who had more brothers than sisters, also had higher chances of having more sons.

In the study, the researchers analyzed the data on 927 family information charts that included 556,387 European and North American people back in sixteenth century.

However, the researchers didn’t find the same link in women for their sibling and offspring sex.

A specific way for genes influence on baby’s sex has not been proven yet.

A woman can pass only X chromosome through her egg into her child and it is man who  can decide his child sex by passing X or Y chromosome that make them boy or girl( Y for boy and X for girl).

The birthrate of 50-50 shows that men deliver almost an equal amount of sperms with X or Y, but the researchers suspect that this balance has shifted in the favor of either sex in some couples.

There are different explanations for this that include time amount that sperms have to spend in testicles while waiting and the difference in monthly cycle of woman and the time of having sex.

The new study, led by Dr Corry Gellatly, shows that there is defiantly a genetic factor working behind.