The most obvious, visible different in people is their physical size. Some people are taller, stronger, heavier than others. Women, expecially, are generally shorter, lighter, and not having had a strong, muscle-developing steriod (testosterone), are not as muscular.
While this may be a "fact of life", it is also used creatively to make sure that some people aren't able to do some tasks or jobs.
for example, orthopedic surgons at one time to be big, husky guys: they had to physically move bones even when the patient's muscles were resisting
but now, with orthoscopic surgery and robotic assistents, this is not the case.
In this book, I'll look at how what is relatively minor physical strenght and size difference is used by some to manipulate the enviorment so as to elminiate more qualified competitors.