RH Negativity Is Not Alien

There is an idea circulating on the internet that RH negativity is evidence of humans having been hybridized with aliens, either through breeding or genetic engineering. This idea misunderstands the science of RH negativity.

A good introduction is Why Rh Negative is not Blood of Gods or of Alien Origin. It says:

While the ABO classification is based on the two antigens A and B, the Rh group has 50 antigens! However, the main Rh classification is based on one single antigen of special importance, called the D antigen. So, if your blood has the Rh D antigen, then your blood group is Rh+, else it is Rh-. The reason for the importance of this antigen is that a mismatch in the D antigen can prove fatal during blood transfusion [...]

If the mother’s immune system has prior [exposure to the] Rh D antigen, either due to some previous blood transfusion of Rh+ blood, or if this is not the first pregnancy and the earlier pregnancies carried a Rh+ child, then the mother’s immune system is already aware of Rh D antigen and has antibodies against it ready, which can be of an immediate concern for the fetus health. [...]

Rh- indicates the absence of the Rh D antigen which otherwise is quite abundant in most (85%) humans. So what could be the contribution of alien blood here? Obviously, there is nothing alien here, because there is no alien genes present here, it's actually the “absence” of our own genes which produce the Rh D antigen in most humans.

The last sentence is wrong. Absence of an antigen can of course come from breeding, because that is how RH- people acquire it. RH negativity is recessive, so to be RH- you have to get from each of your parents a version of the RH blood group that omits the RH D gene. But the article goes on to correctly point out that a maternal immune reaction to the child does not suggest alien breeding:

We have seen newborns die because of this attack even in horses, cats and dogs! Read about Neonatal isoerythrolysis. [This happens] in all those species where the mother has a negative antigen blood group, and the fetus has a positive antigen blood group, and mother’s blood comes in contact with fetal blood. 

For that matter, [in humans] it is not only restricted to Rh D antigen either. It is also very much possible that mother whose blood group is O, gives birth to a child whose blood group is B, and if the mother’s blood comes in contact with fetal blood, then there will be antibodies against B produced by the mother’s blood! It's only that in this case it is not life threatening, while in the case of Rh D it can be life threatening to the baby.

The article then asks: why does the mother's immune system react so violently to RH D? It answers:

Some recent studies have indicated that Rh- people are resistant to some parasites like Toxoplasma. So it might have served an advantage [in European populations] NOT to have the Rh D antigen. 

One can find many such instances across human evolution. For example, humans who come from an ancestry which started domesticating cattle and consuming dairy products have digestive systems which generate an enzyme called lactase which helps in digesting [the lactose in] milk. However, a significant population of humans are lactose-intolerant, which means they cannot digest milk products. Does this mean lactose-intolerant population are from an alien ancestry? 

Some evolutionary gene modifications might prove fatal when expressed, but are nevertheless are useful while [recessed]. For instance, Sickle Cell anemia is a fatal disease where red blood cells [deform to sickle shape] causing life threatening complications. However, those humans who are only carriers of the [recessive] gene causing Sickle Cell Anemia are resistant to Malaria.

A 1997 article in Human Molecular Genetics traces the genetic family tree of the RH blood group: Evolution of the Human RH (Rhesus) Blood Group Genes: A 50 Year Old Prediction (Partially) Fulfilled. Using blood from different people possessing various haplotypes of the RH blood group, the authors sequenced the exact parts of chromosome 1 that control these antigens. 

The high degree of homology between the coding regions of the RHCE and RHD genes is consistent with an ancestral gene duplication. The ∼4% divergence over the coding region would suggest, assuming an average nucleotide substitution rate of 4 × 10−9 per nucleotide per year, that duplication occurred some 10 million years BP. This timing is consistent with the finding that the gorilla and chimpanzee are unique among the anthropoid apes in expressing homologues of both the human D and c antigens [...]

So any alien hybridization or genetic engineering had to happen 10 million years ago, and was performed on a common ancestor to humans, apes, and chimps. Those were very patient aliens!

Another article summarizes what is known about the origin of RH D:

The Rh blood group system consists of two genes RHD and RHCE on chromosome 1, positioned in opposite directions and separated by 31.8 kb, in which the TMEM50A gene (previously SMP1) is located. The RHD gene arose as a duplication of the RHCE gene in the common ancestors of humans, chimpanzees, and gorillas [37]. Both genes have 10 exons and share an overall 93.8% gene sequence identity and 96.4% exon sequence identity [38,39]. The RHD gene is flanked by two 9 kb regions of 98.6% homology, the so-called Rh boxes. [...]

At present (December 2017), 54 antigens, 378 RHD alleles, and 116 RHCE alleles have been recognized in the Rh blood group system. The main mechanism responsible for the generation of hybrid RH genes is thought to be gene conversion, explained by the opposite orientation of the highly homologous RHD and RHCE genes. Multiple exons can be converted, but often microconversion events lead to single amino acid changes. 

So not only do we know that RH D arose 10M years ago, but we also know what kind of mutation caused it. And we know that it is just one of many mutations that have happened in the RHCE and RHD genes, yielding a myriad of human haplotypes besides the A/B/O/Rh-D combinations that we so often hear about. (See here for lists of the many blood group variants in gorillas, chimps, pygmy chimps, orangutans, gibbons, macaques, and a dozen monkey species.)

If the omission of RH D is alien handiwork, then it was disguised to look very much like all the other random small antigen mutations in these genes across all these primates. It just so happens that one of these 54 human antigens can sometimes have devastating maternal-fetal interactions, but has not been evolved out of our genome. Evolution is not perfect, but it's always trying to make us better -- and that means it sometimes makes us worse.

Summary: If something walks, swims, and quacks like a random 10Myr-old mutation, it's probably just that, and not alien breeding.