Another theory supposedly contradicting the equally unproven claim that Neanderthals were blood type O negative is the one, that Cro-Magnons were rh negative. In short terms: There is zero evidence of that anywhere. All you will be able to read online are fabrications. Who exactly the Cro-Magnons were in itself is up for debate and their blood types were definitely not known. As for the Neanderthals: 2 eastern specimens examined were rh +/+. The Spanish examinations were revealed as O, no rh indicated. There are certain similarities between Neanderthals and rh negative populations today. That doesn’t mean they were rh-. A lot is yet to be examined.