What is inheritance?

The original meaning of a gene was simply a heritable unit. This was long before the discovery of DNA. The theory was based on phenotype, i.e., observable characteristics. What they didn’t know and what still doesn’t often get acknowledged is that much gets inherited from parents, especially from the mother. This includes everything from epigenetics to microbiome, the former determining which genes express and how they express while the latter consists of the majority of genetics in the human body. The fetus will also inherit health conditions from the mother, such as malnutrition and stress, viruses and parasites — all of those surely having epigenetic effects that could get passed on for generations.

Even more interestingly, DNA itself gets passed on in diverse ways. Viruses will snip out sections of DNA and then put them into the DNA of new hosts. Mothers, including surrogate mothers, can gain DNA from the fetuses they carry. And then those mothers can pass that DNA to any fetus she carries after that, which could cause a fetus to have DNA from two fathers. Fetuses can also absorb the DNA from fraternal twins or even entirely absorb the other fetus, forming what is called a chimera. Bone marrow transplantees also become chimeras because they inherit the stem cells for blood cells from the donor, along with inheriting epigentics from the donor. These chimeras could pass this on during a transplantee’s pregnancy.

We hardly know what all that might mean. There is no single heritable unit that by itself does anything. That is not the direct source of causation. A gene only acts as part of DNA within a specific cell and all of that within the entire biological system existing within specific environmental conditions. The most important causal factors are various. What is in DNA only matters to the degree it is expressed, but what determines its expression will also determine how it expresses. Evelyn Keller Fox writes that, “the causal interactions between DNA, proteins, and trait development are so entangled, so dynamic, and so dependent on context that the very question of what genes do no longer makes much sense. Indeed, biologists are no longer confident that it is possible to provide an unambiguous answer to the question of what a gene is. The particulate gene is a concept that has become increasingly ambiguous and unstable, and some scientists have begun to argue that the concept has outlived its productive prime” (The Mirage of a Space between Nature and Nurture, p. 50). Gene expression as seen in phenotype is determined by a complex system of overlapping factors. Talk of genes doesn’t help us much, if at all. And heritability rates tells us absolutely nothing about the details, such as distinguishing what exactly is a gene as a heritable unit and causal factor, much less differentiating that from everything else. As Fox further explains:

“It is true that many authors continue to refer to genes, but I suspect that this is largely due to the lack of a better terminology. In any case, continuing reference to “genes” does not obscure the fact that the early notion of clearly identifiable, particulate units of inheritance— which not only can be associated with particular traits, but also serve as agents whose actions produce those traits— has become hopelessly confounded by what we have learned about the intricacies of genetic processes. Furthermore, recent experimental focus has shifted away from the structural composition of DNA to the variety of sequences on DNA that can be made available for (or blocked from) transcription— in other words, the focus is now on gene expression. Finally, and relatedly, it has become evident that nucleotide sequences are used not only to provide transcripts for protein synthesis, but also for multilevel systems of regulation at the level of transcription, translation, and posttranslational dynamics. None of this need impede our ability to correlate differences in sequence with phenotypic differences, but it does give us a picture of such an immensely complex causal dynamic between DNA, RNA, and protein molecules as to definitely put to rest all hopes of a simple parsing of causal factors. Because of this, today’s biologists are far less likely than their predecessors were to attribute causal agency either to genes or to DNA itself— recognizing that, however crucial the role of DNA in development and evolution, by itself, DNA doesn’t do anything. It does not make a trait; it does not even encode a program for development. Rather, it is more accurate to think of DNA as a standing resource on which a cell can draw for survival and reproduction, a resource it can deploy in many different ways, a resource so rich as to enable the cell to respond to its changing environment with immense subtlety and variety. As a resource, DNA is indispensable; it can even be said to be a primary resource. But a cell’s DNA is always and necessarily embedded in an immensely complex and entangled system of interacting resources that are, collectively, what give rise to the development of traits. Not surprisingly, the causal dynamics of the process by which development unfolds are also complex and entangled, involving causal influences that extend upward, downward, and sideways.” (pp. 50-52)

Even something seemingly as simple as gender is far from simple. Claire Ainsworth has a fascinating piece, Sex redefined (nature.com), where she describes the new understanding that has developed. She writes that, “Sex can be much more complicated than it at first seems. According to the simple scenario, the presence or absence of a Y chromosome is what counts: with it, you are male, and without it, you are female. But doctors have long known that some people straddle the boundary — their sex chromosomes say one thing, but their gonads (ovaries or testes) or sexual anatomy say another. Parents of children with these kinds of conditions — known as intersex conditions, or differences or disorders of sex development (DSDs) — often face difficult decisions about whether to bring up their child as a boy or a girl.”

This isn’t all that rare considering that, “Some researchers now say that as many as 1 person in 100 has some form of DSD.” And, “What’s more, new technologies in DNA sequencing and cell biology are revealing that almost everyone is, to varying degrees, a patchwork of genetically distinct cells, some with a sex that might not match that of the rest of their body. Some studies even suggest that the sex of each cell drives its behaviour, through a complicated network of molecular interactions. Gender should be one of the most obvious areas to prove genetic determinism, if it could be proven. But clearly there is more going on here. The inheritance and expression of traits is a messy process. And we are barely scratching the surface. I haven’t seen any research that explores how epigenetics, microbiome, etc could influence gender or similar developmental results.


Racial Perceptions and Genetic Admixtures

As to who is a Negro in the United States, I have come to the
conclusion after long and careful thought that to be an expert on
that subject the first qualification is to be crazy. Only those who
are able to throw all logic, all reasoning to the winds, can ever
hope to be authorities on that matter.
~ J. A. Rogers. The World’s Greatest Men of Color.

I came across further data on genetic admixtures in the American population. I’ve discussed some of this before, but a summary of the key data seemed in order.

First, there is more diversity among Africans than there are between all other geographic populations in the world. As stated by Rotimi (in Genetic ancestry tracing and the African identity: a double-edged sword?), “that African populations have more genetic variation between them (estimates are as high as 95%) than when Africans are compared to other peoples who migrated out of Africa thousands of years ago (estimates are as low as 3%)” It would make more sense to combine all non-Africans as a single race than to combine Africans as a single race.

Besides, all diversity in all populations exists in a continuum and phenotype features exist on a gradient (e.g., lighter to darker skin), the reason being that various genetic clusters exist across geographic populations. This is why Southern Europeans have more genetic diversity in a way that is more similar to Africans than to Northern Europeans. After all, Southern Europeans have shared more genetic history and proximity with Africans and other Mediterranean populations.

Which genetic cluster one focuses on will determine how one sees various populations as similar or dissimilar. The greatest diversity of such clusters, though, will be found among Africans rather than between Africans and non-Africans. Appearances such as skin color are genetically deceiving. Or to put it scientifically: There are many genotypes that can contribute to the same or similar phenotypes.

Second,  African-Americans have on average 20-25% European genetics (although some studies show it as low as 18% and some as high as 30%). This makes sense since, as Henry Louis Gates Jr explains, “As we have shown in the “African American Lives” series on PBS, […] between 30 and 35 percent of all African American males can trace their paternal lineage (their y-DNA) to a white man who impregnated a black female most probably during slavery.”

More interesting, at least 5% of African-Americans have more than 50% European genetics and a recent study (Shriver) puts that at about 10% of African-Americans. Some African-Americans are almost entirely European, except for a tiny percentage of African genetics. “People who identify as African-American may be as little as 1 percent West African or as much as 99 percent”, according to Genetic study clarifies African and African-American ancestry (Phys.org). Some studies have even found that 5.5% of so-called African-Americans had no detectable African genetics.

Taken together, this means that at least in some ways African-Americans are even more genetically diverse than the African populations that are part of their ancestry. African-Americans include the ancestors of the original slaves from West Africa and other slaves from the non-Anglo-American colonies with various other admixtures, Jamaicans in particular being highly diverse. Also included are the newer immigrants who have no enslaved ancestors and who come from every region of Africa, thus bringing with them that immense genetic diversity.

A not insignificant point is that a large number of African-Americans should be more accurately designated as European-Americans. Just think about this. Whenever you pass a group of ‘black’ people, the probability is that at least one of them is actually mostly European and may have very little or no African genetics. Indeed, if you suspend the typical American racial biases, you’ll notice most ‘black’ Americans do have lighter skin than the average African, often as light skinned as other non-African people including many Southern Europeans.

A person can have mostly European genetics and still have darker skin and wavy hair that they inherited from African ancestry even without any slave ancestors (after all, skin and hair genetics are only a small percentage of inherited genetics). Why aren’t dark-skinned, dark-wavy-haired Europeans  such as Italians more accurately called African-Europeans? Why aren’t dark-skinned, dark-wavy-haired Italian-Americans more accurately called African-European-Americans?

On the opposite end of the spectrum, a person can have ‘white’ features while having a ‘black’ great grandparent or several ‘black’ great great grandparents. Even a single ‘black’ grandparent wouldn’t necessarily lead to a person being noticeably non-‘white’, depending on the genetics inherited. A genetic analysis of James D. Watson’s DNA, following some racist remarks he made about Africans, claimed to have shown he had 16% African genetics (and 9% Asian genetics for a total of 25% non-European genetics). Another self-identified white researcher, Mark D. Shriver, found he had 20% African genetics. Watson and Shriver look as white as can be and neither of their families have any stories about black ancestry. Around a third (30%) of white Americans has the equivalent of three African ancestors in recent centuries (2.3% African genetics).

Here is an interesting way to think about it (Stephan Palmié, Genomics, Divination, “Racecraft”):

“As Stuckert (1976) has pointed out in an ingenuous statistical extrapolation from historical records, by the time of the 1970 U.S. census, some 24% of all persons listed as “white” might reasonably have been presumed to have had African ancestors, while more than 80% of all “blacks” would have had non-African ancestors. Transformed into numerical values, this means nothing less than that the overwhelming majority of all Americans of African ancestry – i.e. about 42 millions at the time – had not been counted into the black population (which then stood at 22 millions), but classified as white. Put differently, there were (and surely still are) almost double the number of “white”Americans of African descent as “black” ones (cf. Palmié 2002).”

This is far from commonsense, according to our standard assumptions. ‘White’ Americans with African genetics are a smaller percentage of the total ‘white’ American population as compared to the percentage found in ‘black’ Americans. However, since the white population is larger, the raw number of ‘white’ Americans with African genetics is larger than the raw number of ‘black’ Americans with African genetics.

The US population is genetically mixed to a greater extent than most people would have predicted and more than the racial realists/purists would have preferred. Since the miscegenation laws ended, this mixing has been increasing generation after generation. All the above numbers would be even higher for the younger generations. As far as that goes, these kinds of admixtures are already higher in most countries around the world. To speak of ‘blacks’ and ‘whites’ as general categories for all countries, the US is highly unusual in having relatively low rates of admixture. It isn’t just unusual, but maybe a bit unnatural.

In conclusion, ultimately race is an arbitrary social construct. Yes, it is real to the extent that, like any social construct, it can be enforced onto a population. But no, it isn’t inherent to genetics as an a priori reality. Plus, even with centuries of enforced genetic segregation, much of racial identity requires subjective perception and still perception often fails to tell us much about the actual genetics of individuals.

You have to be looking for the social construct of race in order to find it, both in appearances or in genetics. There are millions of distinctions between humans and hypothetically any or all of these could be called races. The point is that the folk taxonomy of races doesn’t fit the data, although one can cherrypick data to fit whatever theory one wishes to prove by way of circular reasoning. In the end, though, it just doesn’t add up to a plausible scientific theory. The relationship between genotype and phenotype is too complex and nuanced for centuries old non-scientific racist categories.

See below for more info:

Our Hidden African Ancestry
by ScottH

Researchers at 23andMe looked at the genetic ancestry of about 78,000 customers likely to consider themselves as entirely of European ancestry and found that somewhere between 3 percent and 4 percent of those people have “hidden” African ancestry.

The percent of African ancestry is relatively low with the majority of individuals having just 0.5 percent to 0.75 percent — which suggests that those people have an African ancestor who lived about six generations, or about 200 years, ago.

This is by no means meant to represent the percent of African ancestry among those who identify themselves as being of European descent across America. It is simply a snapshot of those in our database at this time. Our researchers have also excluded those with more than 5 percent African ancestry with the assumption that it’s more likely that their ancestry is known. That doesn’t mean it is known, just as it doesn’t mean that those of European descent with 5 percent or less African ancestry are unaware of it. In addition, our database includes customers who are actually European so the actual percentage of Americans of European descent in our database who have African ancestry may be higher.

But we believe this is the first detailed look of the African ancestry among those who consider themselves white. It begs many questions for possible future study. For instance, looking at the generational distribution implied by the percentages it appears most of the mixing occurred 200 years ago or more. Was intermixing between black and white more acceptable during that time in American history? Or was the relative isolation of people then such that the societal taboos against such mixing were more lax?

At the very least these findings suggest a more nuanced picture of race relations at that time.

Afro-European Genetic Admixture in the United States
Essays on the Color Line and the One-Drop Rule
by Frank W Sweet

With this added information, three aspects of the scatter diagram suddenly jump out at you. First, there is significant overlap between White and Black Americans regarding Afro-European genetic admixture. Some so-called “Black” Americans have less DNA admixture of African ancestral origin than do some so-called “White” Americans. Second, the admixture range of Black Americans spans the entire chart. While most of the subjects who self-identify as Black (marked as circles) have strong African admixture (are found towards the right), some have little or no African admixture (are found at the left edge). Finally, although the range of genetic admixture in those who self-identify as “White” is narrower than the admixture range of Blacks, it is still significant. Many so-called “White” Americans have as much as 20 percent or more of African genetic admixture.

[ . . . ] Three points of interest present themselves upon your examining this graph. First, as in the prior chart, there is genetic admixture overlap between Americans of the Black and White endogamous groups within the range of from zero to thirty percent African genetic admixture. As in the Shriver study of skin tone, some so-called “White” Americans have over twenty percent African genetic admixture and some so-called “Black” Americans have little or none. Indeed, other studies have found that approximately 5.5 percent of members of the U.S. Black community have no detectable African genetic admixture.15

Second, the Black and White groups are not symmetrical. The mean African admixture among White Americans is low—roughly 0.7 percent African and 99.3 percent European admixture.16 To put this in perspective, this would have been the result if every member of the U.S. White endogamous group alive today had a single ancestor of one hundred percent African genetic admixture seven generations ago (around the year 1850). Of course, African alleles are not distributed evenly. Seventy percent of White Americans (like 5.5 percent of Blacks) have no detectable African genetic admixture at all. Among the thirty percent of Whites with African genetic admixture, the admixture ratio averages to about 2.3 percent, the equivalent of having a single ancestor of one hundred percent African genetic admixture from around the year 1880.17 Black Americans, on the other hand, have significant European admixture (averaging about 75 percent African and 25 percent European).

Third, the wide admixture spread of the two groups of New-World inhabitants contrasts with the narrow range of admixtures among Old-World inhabitants. A wide spread of genetic admixtures is characteristic of the Western Hemisphere. As evident in the chart, on the one hand, the U.S. White population spans a range of 15-20 percent and the U.S. Black population covers a 30-40-percent range. On the other hand, the Nigerian population covers only a 10-precent spread and the Congolese population spans only a 5-percent range.

[ . . . ] About one-third of White Americans are of between two and twenty percent recent African genetic admixture, as measured by the ancestry-informative markers in their DNA.19 This comes to about 74 million Americans. And yet, day-to-day experience teaches that virtually all White Americans look, well, White. Some may look more Mediterranean and others may look more Nordic, but very few White Americans have a distinctively African appearance.

[ . . . ] And so, why do few if any White Americans display a strongly African appearance (have a high melanin index) despite having detectable African admixture? Because those Americans who “look Black” are assigned involuntarily to the Black endogamous group, whatever their genetic admixture. The scatter diagrams of the two endogamous U.S. groups are not symmetrical because the selection process acts only upon the White group. As revealed in court records, discussed elsewhere, a person of mixed ancestry who “looks European” (like Dr. Shriver or his maternal grandfather) in practice has the option of either adopting a White self-identity, thus joining the White endogamous group or a Black self-identity, thus joining the other group. But a person of mixed ancestry who “looks African” lacks such a choice. U.S. society assigns such a person to membership in the Black endogamous group, like it or not.25

In conclusion, U.S. society has unwittingly applied selection pressure to the color line. The only American families accepted into the White endogamous group have been those whose African admixture just happened not to include the half-dozen alleles for dark skin (or the other physical traits associated with “race”). Since those particular alleles were sifted out of the portion of the White population that originated in biracial families, the relative percentage of the remaining, invisible, African alleles in this population cannot affect skin color. That skin-color does not vary with African genetic admixture among American Whites, despite their measureably recent African admixture, demonstrates and confirms that physical appearance has been an important endogamous group membership criterion throughout U.S. history. It has resulted in genetic selection of the White U.S. population for a European “racial” appearance, regardless of their underlying continent-of-ancestry admixture ratio.