Are sagittal keels rare?

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Wikipedia says they are rare:

However, there is a very small portion of modern humans who have this, but its function and etiology are unknown. Patrick Stewart of Star Trek: The Next Generation and the martial artist Shi Yan Ming present good examples of modern humans (Homo sapiens sapiens) with this feature. Australian Aborigenes also possess it.

but doesn't include a source.

However, if we use Patrick Stewart a a benchmark, other actors have it too. (Some of these pics were first posted by other forum members)









Soccer players:







I have to say that where I live there is a lot of bald people, but I don't recall seeing a sagittal keel in the wild. So what's the deal? Are they rare, like Wikipedia claims? What percentage of male population has them?

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Another one: