Well..
I have to say that Girls can be stronger then certain boys, but not all girls are stronger then all the boys.
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Boys, once in puberty, develop more muscle mass than girls which continues into adulthood. However, before puberty, boys and girls are pretty much equal in potential muscle strength.
I wouldn't say boys are stronger biologically. Have you noticed that women outlive men and tend to be less prone to disease and other maladies. Girls have a lower infant mortality rate too. Girls also generally mature faster than boys physically, emotionally, and often academically - especially in language.
In other words, most boys are physically stronger then the average female, only because their muscle mass is built up differently from girls. And as for girls, we mature quickly. So it's basically the same thing. All part of puberty my dear.
But it doesn't mean all boys are stronger then girls. There are very strong girls, and very weak boys vice versa.
So I disgaree, both sides are equal. Because no sex is greater than the other sex.