No race is a different species.

modern humans;
(hyo͞o′mən) 1. A member of the species Homo sapiens; a human being. 2. A member of any of the extinct species of the genus Homo, such as Homo erectus or Homo habilis, that are considered ancestral or closely related to modern humans.

Not only are all humans modern humans, but anatomically modern humans, well would you look at that, originated in Africa.

Traditionally, subspecies are seen as geographically isolated and genetically differentiated populations. Studies of human genetic variation show that human populations are not geographically isolated, and their genetic differences are far smaller than those among comparable subspecies.

We, by definition, cannot be classified into different subspecies.

Archaic humans went extinct long ago.

Anatomically modern humans appear from over 160,000 years ago in Ethiopia and after 70,000 years ago (see Toba catastrophe theory), gradually supplanting the "archaic" human varieties. Non-modern varieties of Homo are certain to have survived until after 30,000 years ago, and perhaps until as recently as 12,000 years ago. Which of these, if any, are included under the term "archaic human" is a matter of definition and varies among authors. Nonetheless, according to recent genetic studies, modern humans may have bred with "at least two groups" of ancient humans: Neanderthals and Denisovans.[4] Other studies have cast doubt on admixture being the source of the shared genetic markers between archaic and modern humans, pointing to an ancestral origin of the traits which originated 500,000–800,000 years ago.[5][6][7]

ALL humans are Homo Sapiens. No one is less archaic than another.

“ A common criterion for recognizing two distinct populations as subspecies rather than full species is the ability of them to interbreed without a fitness penalty”
Subspecies - Wikipedia

Fitness in the evolutionary context means ability to breed.

Thus neanderthals were a separate subspecies because male hybrid offspring had fitness issues
“While Neanderthal males themselves were likely good at breeding, their half-human sons weren't and "they must have been disappointed in their sons," said Nature co-author Svante Paabo of the Max Planck Institute in Germany.”

The result being no neanderthal influence on the Y chromosome.

Which is also why the descendants and Africans today are the same subspecies - there is no fitness deficit associated with interbreeding between populations in modern humans.

Again, by definition, you cannot validly classify the races into different subspecies. If that were the case, then what about eye colour? Height? Weight? Hair colour? Sex would be a more valid classification for different races than ancestry/ethnicity is. Even if one thinks it is valid to agree that there a subspecies of human, in a taxonomic hierarchy, race and subspecies are equal. There is no objective way to measure superiority.

“Even though there is a broad scientific agreement that essentialist and typological conceptualizations of race are untenable, scientists around the world continue to conceptualize race in widely differing ways, some of which have essentialist implications.[10] While some researchers use the concept of race to make distinctions among fuzzy sets of traits or observable differences in behaviour, others in the scientific community suggest that the idea of race often is used in a naive[5] or simplistic way,[11] and argue that, among humans, race has no taxonomic significance by pointing out that all living humans belong to the same species, Homo sapiens, and (as far as applicable) subspecies, Homo sapiens sapiens.[12][13]”

“Estimating our ancestral composition down to 0.1% seem to suggest that there are exact, categorical divisions between human populations. But reality is far less simple. Compared to the general public’s enthusiasm for ancestry testing, the reaction from scientists has been considerably more lukewarm. Research indicates that the concept of “five races” does, to an extent, describe the way human populations are distributed among the continents—but the lines between races are much more blurred than ancestry testing companies would have us believe “

A landmark 2002 study by Stanford scientists examined the question of human diversity by looking at the distribution across seven major geographical regions of 4,000 alleles. Alleles are the different “flavors” of a gene. For instance, all humans have the same genes that code for hair: the different alleles are why hair comes in all types of colors and textures.

In the Stanford study, over 92% of alleles were found in two or more regions, and almost half of the alleles studied were present in all seven major geographical regions. The observation that the vast majority of the alleles were shared over multiple regions, or even throughout the entire world, points to the fundamental similarity of all people around the world—an idea that has been supported by many other studies (Figure 1B).

If separate racial or ethnic groups actually existed, we would expect to find “trademark” alleles and other genetic features that are characteristic of a single group but not present in any others. However, the 2002 Stanford study found that only 7.4% of over 4000 alleles were specific to one geographical region. Furthermore, even when region-specific alleles did appear, they only occurred in about 1% of the people from that region—hardly enough to be any kind of trademark. Thus, there is no evidence that the groups we commonly call “races” have distinct, unifying genetic identities. In fact, there is ample variation within races (Figure 1B).

Ultimately, there is so much ambiguity between the races, and so much variation within them, that two people of European descent may be more genetically similar to an Asian person than they are to each other (Figure 2).

https://www.genome.gov/about-genomics/fact-sheets/Genetics-vs-Genomics

Mixed children do not face higher health risks:

Most studies are based on clinical reports or reports of mixed-race samples without comparison to single-race groups. It is not surprising that such samples lead to the conclusion of emotional and behavior problems, as clinical samples are self-selected for problems. No national data on adolescents have been reported, except from the sample we used.

“The most common explanation for the high-risk status is the struggle with identity formation, leading to lack of self-esteem, social isolation, and problems of family dynamics in mixed-race households.1–6 This literature is not entirely consistent. In some studies no differences are found between mixed-race and single-race children.7–9 This article explores the risk status of self-identified mixed-race compared with single-race adolescents using a large, nationally representative sample.”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1448064/

You said "The grey substance of the brain of a Negro is of a darker color than that of the European, that the whole brain is of a smokey tint, and that the pia mater [the innermost membrane covering the brain] contains brown spots, which are never found in the brain of a European."

Are you referring to melanin in the brain (neuromelanin)? Because the effects of neuromelanin in the brain are only positive (superior athletic ability, superior learning ability)

Smoking patterns and health consequences have been shown to vary widely between Black and White smokers. For example, smoking prevalence is lower among Blacks (19.8%) than Whites (21.4%),1 Blacks smoke fewer cigarettes per day,2,3 Blacks have reported equal or higher desire to quit smoking.

“The total and nonrenal clearances of nicotine were not significantly different, respectively, in blacks (17.7 and 17.2 mL·min−1·kg−1) compared with whites (19.6 and 18.9 mL·min−1·kg−1) (P=.11 and .20). However, the total and nonrenal clearances of cotinine were significantly lower, respectively, in blacks (0.56 and 0.47 mL·min−1·kg−1) than in whites (0.68 vs 0.61 mL·min−1·kg−1; P =.009 for each comparison). The nicotine intake per cigarette was 30% greater in blacks compared with whites (1.41 vs 1.09 mg per cigarette, respectively; P =.02)”

Also more blacks smoke menthol cigarettes. Menthol cigarettes are suggested to be more addictive.

“Menthol smokers show significantly higher levels of nicotine addiction compared with non menthol smokers in the same age group. Menthol may help to cover the actual strength of cigarette smoke making it more pleasurable and more difficult to quit.”

Why group every single member of genetic ancestry together as if averages aren’t just averages but represent every single human being? After all, the genetic variation within groups is far greater than the differences between them.

BRAIN DIFFERENCES

As I said Africa has many population clusters and the greatest genetic diversity. Some separate population clusters even live in different parts of the same country. It's pretty unscientific to group them all together as (Negroid).
I really think you have a strange concept of how academia works. It's not a matter of people being "squeamish" or a taboo about the research. They just kind of feel it would be like trying to disprove gravity.

What we know about evolution and how long it takes, doesn't support "sub-speciation." It takes about 1 million years for significant evolutionary change to occur even in extreme isolation. Humans left Africa about 100,000-50,000 years ago, so that is not enough time for significant changes to occur genetically except for the phenotypical adaptations most relevant to environment, i.e. skin color, which is why you have people in equatorial regions of Southeast Asia and Australian aborigines with skin almost as dark as black Africans, but totally different genetics.
Furthermore, the selection mechanism of evolution obviously started to slow down as societies settled and formed civilizations. For natural selection to occur, poor adaptation to a species environment has to prevent the species from reaching reproductive age. Once settled, most humans were able to reach reproductive age with no problem, so evolution slowed down and largely became a social phenomenon of adapting, not genetically but through forms of social organization and technology.
3.) The biological definition for race and subspecies is about 17 percent to 25 percent genetic difference. The general consensus among the genetics community is that Genetic difference between any given population is less than 10 percent.
So as you can see, it's not "sociology" or the "humanities" that define race as a social construct. It's the hard sciences, i.e. biology and genetics, that take this view. The only dissenters against this consensus are all in the soft sciences (mostly psychology) and the vast majority of them (Jensen, Rushton, Gottfredson, Lynn, MacDonald) are funded by the Pioneer Fund, which got its start collaborating with Nazi eugenicists.
If Steve Hsu is the best example of someone in the natural sciences, you can come up with, then you're in trouble. "But he's a theoretical physicist, so he must be smart, right?" Yeah, but he also authored a bunch of Bible books and religion and Biology aren't exactly sympatico. Ben Carson is a brain surgeon, but I don't really trust his theories about who built the pyramids and for what purpose.

the difference is actually marginal when you consider that the amount of variation within groups is about 130 cu. cm. Brain size is very weakly correlated with IQ. In vivo brain size isn't necessarily genetic. The brain is plastic. It's size is not fixed. You can increase the size of your brain by learning to juggle. Environmental factors can affect your brain size like lead exposure in infancy/childhood as well as maternal nutrition.

Also, Nisbett compared the average black brain size to measurements of Einstein's brain and the average was higher. Furthermore, most research seems to point to intelligence being a function of brain structure not size.

One of the studies you cited (the ..) explicitly stated that their physique was poor, and implies that the selected Kenyan might have been malnourished. This was also, only 1 person.