Since my childhood, I have so often witnessed a fallacy in common thinking about the expertise borne out of hard work. As soon as you mention "ABC was born to be a Mathematician," people start getting cynical and come up with a hundred arguments in favour of 'everyone is equal.' The arguments are just, but not required.
Confusing 'everyone is equal' as in potential, with 'everyone is equal' in its actualization, is generally borne out of childhood moral teachings, which righteously tell you that everyone is equal. In any case, you must pay attention to the effort that goes into any kind of expertise in any subject. If you keep that in mind, though everyone is equal, as far as potential is concerned, the difference is made by sustained effort supported by the natural inclinations, which in turn are because of 'samskaras' from previous births.
Everyone is equal when you talk about potential. Everyone has same potential, you may say--like every Uranium atom is capable of generating the same amount of nuclear energy. But the difference comes into picture when you start analyzing various fields of activity and that is precisely because of the amount of effort that has been put by various subjects. I take liberty of using theory of incarnation to support my propositions in these matters.
An interlocutor very recently suggested that "Everyone is equally capable of being philosophical on a subject." I contend against him unless he clearly differentiates between actualization and potential. Some people are more of artists, scientists, philosophers or doctors because they have put much effort in those directions in their previous lives.
I also think that anyone is capable of being anything. My suggestion is more about propensity, about inclinations, rather than being about 'potential' of subjects.
Some people are drawn more to certain fields than others and this is true despite having almost same surroundings for subjects in question.
Those who use 'reincarnation' as a theory to explain certain things; and I belong to those people, suggest that subtle impressions from your former lives, as remnants of your work and as very refined Karmic vectors drive you naturally to certain fields, which means, if you had studied Mathematics, in your earlier incarnations and loved the subject, you're very likely to be inclined to Mathematics right from your childhood in this incarnation.
This is just a theory. I don't suggest that anyone is any less or more capable than anyone else if you look at the 'whole', but certainly if you take at any given moment, a Leibniz or an Aristotle, you cannot compare him with a common man who is not driven to search for Truth; though they have same potential for every field of human endeavor.