Until the 20th century, most people believed that human varieties were like animal and plant varieties, which can reasonably be expected to display heritable, variety-specific physical and psychological traits.<p>This expectation is a prior, or null hypothesis; evidence is required to refute it.  For instance, if you claimed that Great Danes are just as good as border collies at herding sheep, you&#x27;d have to present evidence to support this claim, which otherwise seems implausible.<p>Military and political events in the 20th century reversed this burden of proof.  The null hypothesis is now that all dogs are equal, at least behaviorally.  If you want to claim that Great Danes aren&#x27;t likely to be good sheepdogs, you have to present evidence showing their inferior performance on herding tasks, and your evidence has to rule out all non-genetic factors.  For instance, obviously if your border collies grew up in the sheep pen and your Great Danes didn&#x27;t, that&#x27;s a valid non-genetic explanation.  It&#x27;s not especially difficult to raise the bar indefinitely on this test.<p>Well, okay, we haven&#x27;t changed our minds about collies, Great Danes and sheep-herding.  But we have changed our minds about Ashkenazi Jews, Australian aboriginals, and chess.<p>The &quot;out of Africa&quot; narrative suggested considerable genetic homogeneity that supported this politically desirable narrative of universal behavioral equality as a null hypothesis.  Recent discoveries in the complex history of human DNA have not been favorable to this narrative.<p>One of the most interesting discoveries is haplogroup A00, a Y chromosome with a divergence time which could be almost 600,000 years ago [1].  This precedes our current use of the species name &quot;Homo sapiens.&quot;  23andme now reports estimated Neanderthal ancestry, but to my knowledge they&#x27;re not telling anyone they have &quot;the erectus chromosome.&quot;<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Haplogroup_A_(Y-DNA)#A00_.28Perry.27s_Y-chromosome.29" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Haplogroup_A_(Y-DNA)#A00_.28Pe...</a>