but I just don't think it's practical.
I recognize the pragmatic value of the practical rationality you set forth to utilize. I feel, though, that in attempting to be pragmatic in your understanding you've lost whether or not a distinction (ie skin collor) has a true practical value as a judgment marker.
things like 15% higher testosterone on average start to assert itself.
Things like that become visible; but then figuring out if what is visible is making a practical differences becomes much harder to judge.
MANY jokes by black comedians.
I, also, recognize that a way to gain a more honest insight into a population is to see what kind of stories/jokes they ascribe to/find funny. Despite this, stories/jokes exaggerated minor differences and make no distinction regarding what has lead to the final state that you see.
But this can be problematic as building a network of supporting 'fact', all of which may be wrong, creates a mindset that can't be overcome by disproving any of those 'facts'. This is how a faith is built and defended: the fog of belief chews up pointed questions; but if you want the answers, you've got to be ready to throw away all of what you believe if countervailing information comes before you.
Biology sets the boundaries. For instance, someone born with Down Syndrome
Sometimes it sets boundaries (no frontal lobe); sometimes it skews (alcoholism runs in the family); sometimes it is irrelevant (ear size)
hundred grams or so of brain weight on average is just going to be meaningless?
The problem with finer distinctions is that they interact in complex ways. To link 'brain size' to 'intelligence' you'll have to start with what part of the brain, why is that being 'bigger' 'better' and then figure out how that 'better' interacts with the rest of the brain. If you get into neuro-psych, which is what my wife is writing her dissertation on, you'll find that brain-structures are rarely deterministic of how one thinks unless there's something missing. IE making the pre-frontal cortex being larger does not make someone better at thinking, even on average.
Egalitarians who argue vs. race realists on YouTube,
I am, indeed, an egalitarian; and I feel that a so-called "race realist" has a grave misunderstanding of how socially constructed things like "race" and "religion" come into being. When you start breaking it down, you'll find that there's more diversity within whites (Irish v. Germans; one WAS-american family v. another) than there is between groups (Chinese v. Indians). So, while you think you are being a realist, you are actually being un-realistic in attributing to all of a group, aspects that vary widely within that group.
well we don't know the exact genes involved so we can't say anything about it yet.
Actually, what I'm trying to do is apply the same rules we use for any other scientific data to race data. If we find that there's significantly greater variation within a group (error) than between groups (effect size) then we aren't justified in concluding that there is a significant difference between groups: (ie there's so much range in each group (whites) that finding an 'average' difference between groups is not something we can say is a reliable difference.