There's also no biological reason 8 billion individual hominids evolved under different conditions and upbringing and nutrition should share the same intellectual capacity, any more than all 8 billion would be equally good sprinters or have the same skin tone or oxygen capacity.
The brain is just another blob of flesh, and what we understand of its capacities suggest it's at least partially inheritable. You'd have to ignore a lot of evidence to believe that all humans are intellectually equal. If there is variation and there is mutation and there are different pockets of populations, there are going to be evolutionary differences between them. Then in terms of sexual selection, we'd have to believe that intelligence as a criterion for mate selection is equally important across cultures, and also impacts offspring fitness the same across all cultures and environments -- vs, say, disease or sun resistance in the tropics. Otherwise, differences would naturally arise over time.
The tricky part is coming up a way to define, much less measure, "intellectual capacity" across different cultures and ways of knowing. IQ tests are pretty biased and arguably a useless measure of evolutionary fitness in many human cultures. Even if you could create the perfect cross-cultural IQ definition and test, administering and collecting such a thing would be nearly impossible in a world where many countries don't even have proper birth records or thorough population censuses (even a basic count, without in-depth testing).
We already know that, within the upper and lower bounds, there can be great variations of "intelligence" WITHIN populations group, as well as smaller differences between them. But we lack the methodology and cultural transparency to be able to accurately measure whether the cross-cultural error bars fall within the intracultural ones. That's not for lack of trying, mind you... many careers have either risen to infamy or else have been destroyed for daring to suggest such things.
In other words, it's not that all humans are equal, it's that we're SO diverse it's hard to group us into neat little groups, whether by race, ancestry, skin color, intelligence, or any other genetic factor. Because the underlying genes themselves don't work that way. They're always changing and competing.
The principles of egalitarianism are a cultural ideal (not shared by much of the world, mind you), not necessarily scientific observations. The scientific input to the ideal, if anything, is not that "the are no differences between groups" but "there are so many differences that these groupings don't really make sense; there are a million other equally valid groupings".
The brain is just another blob of flesh, and what we understand of its capacities suggest it's at least partially inheritable. You'd have to ignore a lot of evidence to believe that all humans are intellectually equal. If there is variation and there is mutation and there are different pockets of populations, there are going to be evolutionary differences between them. Then in terms of sexual selection, we'd have to believe that intelligence as a criterion for mate selection is equally important across cultures, and also impacts offspring fitness the same across all cultures and environments -- vs, say, disease or sun resistance in the tropics. Otherwise, differences would naturally arise over time.
The tricky part is coming up a way to define, much less measure, "intellectual capacity" across different cultures and ways of knowing. IQ tests are pretty biased and arguably a useless measure of evolutionary fitness in many human cultures. Even if you could create the perfect cross-cultural IQ definition and test, administering and collecting such a thing would be nearly impossible in a world where many countries don't even have proper birth records or thorough population censuses (even a basic count, without in-depth testing).
We already know that, within the upper and lower bounds, there can be great variations of "intelligence" WITHIN populations group, as well as smaller differences between them. But we lack the methodology and cultural transparency to be able to accurately measure whether the cross-cultural error bars fall within the intracultural ones. That's not for lack of trying, mind you... many careers have either risen to infamy or else have been destroyed for daring to suggest such things.
In other words, it's not that all humans are equal, it's that we're SO diverse it's hard to group us into neat little groups, whether by race, ancestry, skin color, intelligence, or any other genetic factor. Because the underlying genes themselves don't work that way. They're always changing and competing.
The principles of egalitarianism are a cultural ideal (not shared by much of the world, mind you), not necessarily scientific observations. The scientific input to the ideal, if anything, is not that "the are no differences between groups" but "there are so many differences that these groupings don't really make sense; there are a million other equally valid groupings".