Race is a real and not imaginary construct. There were seven main haplogroups in Africa, L0-L6. L3 split into haplogroup M & N. N being the precursor to caucasians, and M being the precursor to everything else not African. The amount of time that haplogroup M+N have been separated from L is something like 100,000 years. It's not a question of "do races exist", or "are races different", it's only a question of how large of changes can occur in that time span.
That is the sort of horrible simplification that "scientific racists" must make to justify the concept of "race". In those 100 000 years many things happened, such as the peopling of South Asia (Indonesia, Polynesia, etc.) by Neanderthans and other "early humans", then by Negrito-like people, then by "Asians" and "Caucasians" ---with countless mixings and migrations.
(The term "Caucasian", by the way, is a relic from "scientific" racial classifications of the 19th century.)
Darwin's
Origin of the Species impressed on the collective mind the idea that species evolve by branching out in tree-like fashion. Unconsiously, scientists in several other disciplines assumed that their objects of study also evolved by splitting in tree-like fashion. Disciplines where this mistake is endemic include linguistics, history of religions --- and "scientific racism".
However, the branching tree model is not totally accurate even for species. Today we know several instances of "horizontal transmission" -- genes jumping between separate branches of the evolutionary tree. (The tunicates, for example, are a group of species that is high up on the animal branch of the tree, indeed the last branch to split off before the vertebrates; but somehow it acquired genes that enable it to make cellulose -- a feature that is otherwise exclusive of plants. It is believed that some common ancestor of the tunicates somehow incorporated a bit of algal DNA in its own genome. There are known natural mechanisms that allow such jumping, and they have been adapted for genetic engineering. Again, if such an accident happens only once in a million years, that may be sufficient to transfer a gene from one species to all individuals of a completely different species.)
While the branching-tree model is still mostly valid for species, with relatively few exceptions, it is poorly matched to languages, and totally wrong for "races" (or religions). Human populations have continuously split, joined, and mixed through those 100 000 years. Even in historic times Europe and Central Asia witnessed dozens of major genetic/population moves (Indo-Europeans, Greek, Roman, Turks, Muslims, Mongols, "Barbarians"). Same in East Asia, Oceania, and the Amerias. As I noted, even the "modern men" who took over Europe some 30'000 years ago interbred with the Neanderthals who had been there for twice as long or more.
Maps of gene frequencies can be used to guess the migrations in broad terms, but they cannot be used to classify individuals into discrete races. In each population (country, region, ethnic group), the frequency of any marker is almost never 0% or 100%
In America, plenty of Caucasian and Africans live near each other, yet the interbreeding between groups is something miniscule under 5%.
Well, genetic surveys of Brazilians with white skin who believed themselves to be pure "white" (and often had prejudice against "blacks") showed much larger propostion of African genes (40% if I well remember). And that survey (like many in the early days of DNA analysis) only looked at mitochondria or the Y chromosome, that are inherited from father or mother respectively and thus are easier to analyze. But, for the same reason, those analyses fail to measure the true level of mixture in the population. (The myth of the "Seven Eves of Europe" is the sort of nonsense that people can get from badly interpreting such partial studies.)
The 5% that you quote as the US interbreeding, if correct, may reflect the percentage of "whites" with "black" genes, and would be a consequence of the "one drop rule" that (until recently) pushed the children of mixed marriages into the "black" corral. Surely the numbers are very different among the US "blacks".
Since white genes are recessive, the white race would not exist if this ratio was higher. Due to this, whether your Marxist mind acknowledges it or not, if you advocate that everyone on earth interbreed with each other with no regards to race, you are in fact advocating white genocide due to white genes (and Asian) being recessive.
It's pretty easy to verify this with virtually any interracial relationship that exists. Take Heidi Klum for example. Here's her with two of her kids, each from different fathers. She's supposed to be a supermodel, yet has passed along virtually none of those supermodel genes onto one child, while clearly having done so for the other. This is because white genes are recessive and it's hard to even tell the child on the left is related to her at all.
First, there is no such thing as "white genes" and "black genes". There are genes that produce the black skin pigment (an essential protection against sunlight), which are broken or inhibited in people with "white" skin. There are other genes for eye color, hair color, hair wave, etc. The frequency of those genes is very different among populations that have lived for millenia in
relative isolation in northern Europe and Southern Africa (which can be explained by well-known environmental factors, as well as by random drift). Hence, indeed, when individuals from those populations are brought together to the same place, the differences are visually striking. But There are
many more genes whose effects cannot be seen and do not significantly affect survival. There are also many variants of the same gene whose effects are hard or impossible to see visually, and both populations have mixtures of the same variants.
Some of your so-called "white" genes are indeed recessive (like blue eye color), but others are dominant, or have partial effect when two variants are present. But a recessive variant of a gene is not "lost" when it gets paired with a dominant one: the children of two back-eyed persons may be blue-eyed. Ditto for black or blond hair, curly or straight hair, etc..
The important point is that linkage between genes is limited and weak. Therefore, when a "white" population mixes with a "black" one, the first generation children will have one copy of each kind for each gene, but after a couple of generations there will be all combinations -- WW, WB, and BB --
for each gene independently. But the independence of gene mixing, by itself, would imply that racial classifications are meaningless, so "racial scientists" have conveniently developed a blind spot at that place in their minds.
As for that picture, it proves only that Americans have a high incidence of some peculiar genetic defect in their visual system, that renders them unable to perceive gradations of skin color and other "racial" traits. A functioning non-American eye will see that the child at left has a mixture of skin color genes that results in a light brown skin, surely much lighter than the skin color of her African slave ancestor. And you can be sure that she has close to a 50% mix of genes from her two parents, just like the child at right (apart from mitochondial genes
and those in the X chromosomes, which they inherited from the mother alone).
Even among US "blacks", a non-American eye can see many shades of skin pigmentation. In cultures that did not have African slavery for many centuries, or which for some reason never adopted the "one drop rule", skin color is perceived as a continuous variable that is either irrelevant, or does not trigger discrimination at some magic level.
As for anecdotal examples, one of my favorites is a finale of a 40 km Olympic marathon race that I watched many years ago, where the first three to finish were an Italian, a Japanese, and an African (forgot the country, sorry) -- all within a few meters from each other. I take that as evidence that, even with regards to physical stamina -- where genetics could be expected to play an important role -- the differences between those three "races" were on the order of 1 part in 10'000.
