You miss the point. It is obvious that based on genetic criteria, people are not physically equal. Some run faster, some spring higher while others are better at abstraction or emotions. That it is not uniformly distributed among ethnicities is completely irrelevant, and hopefully you'll understand why.
The way we have to consider equality among men is by definition, like an axiom. That way, we can build rules that are much more interesting than the ones where all men are not equal. In particular, it gives you much more liberty, for we consider our society to be above arbitrariness and randomness.
Let's face it, no one chooses where, when and from whom he/she is born, it's either arbitrary (depending on whether you believe in some cosmic plan) or random. The consequences of that is that you are born with a limited amount of possibilities. Now, we can either shorten these possibilities by exploiting this arbitrariness/randomness - it's the "brave new world" scenario where you have to fit that gamma role you were born for -, or we can enlarge them by deciding not to take it into account and state that all human beings are equal. We choose the later since the Declaration of the Rights of Man. It is a great choice based on logical reasoning rather than obsolete bigotry, because it takes into account its consequences. It is a choice that puts forward our capacity (as a species) to think, plan and build, which is by far our greatest ability. But it also as practical advantages for our societies, like a good mix of robustness, resilience and adaptability.