While the accepted answer seems to be "don't ask" -- the researcher in me wants to improve the corpus of knowledge in the world.

If you were hypothetically providing a quality of service that would genuinely be improved be asking for this information, a way could be as follows:

* Optional
* Dropdown

What's in the dropdown is what makes it interesting: Whereas the 3 major "race" descriptors are serious trigger words, the "**subrace**" descriptors have a level of granularity that makes it more interesting (without using the C, M or N words) and potentially less judgmental. 


      Aryan
      Semitic
      Hamitic
      African Negro
      Khoikhoi
      Melanesian
      Negrito
      Australoid
      Dravida & Sinhalese
      North Mongol
      Chinese & Indochinese
      Japanese & Korean
      Tibetan
      Malay
      Polynesian
      Maori
      Micronesian
      Eskimo
      American

Also this level of granularity, being more technical implies that it will be used for a technical purpose.

![enter image description here][1]

People are generally obsessed with themselves and may not even know what sub-race they are yet have a curiosity, so in that spirit provide the information.

Also the time to ask for this is the first time that a diagnosis is being asked for. This both:

* confirms that you're asking for technical reasons.
* is asking at a time when a service is expected to be returned.

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Note: the more interesting question to me is that personally I'm straight-up 50%/50%* ... how do you handle that?

*moreover I just learned what my non-obvious half actually is!

  [1]: https://i.sstatic.net/lZqcC.png