You don't "build tolerance" to UV. Developing a tan will help avoid getting sunburn in the future, but it does nothing at all to reduce your risk of skin cancer. Sunscreen doesn't just stop sunburn, it also prevents cancer.
I mean, there's is a pretty big difference between being born with dark skin and then having your body try to develop it. The difference is skin cancer.
Also, black people get sunburns too, just not nearly as fast.
