There is evidence that the more similar the two people are, the happier their marriage tends to be.

https://www.sciencedirect.com/science/article/pii/019188699190057I

Margi and I have been close since 2005, 13 years ago. Being high-profile White Nationalists, especially between 2009-17 when President Obama personally was after us, has led to incredible economic, health and emotional stresses at times. But we have stayed close and we look similar (see the square chin and strong jawline), we think similarly, and we emote similarly. We both are of Germanic-Keltic stock, a mix of logic, the arts and a fiery defiance of tyranny. 

One study showed that people tend to find their own face when morphed into the opposite sex most attractive, even when he/she doesn’t know it’s his own face, strongly suggesting that people typically prefer those who look like themselves, in other words their own racial/ethnic group.

http://www.psyc.nott.ac.uk/research/vision/jwp/papers/pentonvoak1999.pdf

Hybrid vigor (heterosis) does not seem to apply to humans as we are already very heterozygous, at 0.776

http://mbe.oxfordjournals.org/content/14/7/707.full.pdf

http://www.eebweb.arizona.edu/Courses/Ecol406R_506R/Garcia-Moreno1996-Wolf.pdf

…..oxytocin promotes racial loyalty 

The neurotransmitter oxytocin “makes people more co-operative, benevolent, loyal, generous and trusting of others. It is involved in the parent-child bond – new mothers and fathers have raised levels of oxytocin.

Production also increases when people hug and when they have sex and, recent research suggests, when they receive psychological warmth.”

However, OMG OMG, oxytocin also “fosters racism.” 😉

http://www.guardian.co.uk/technology/2011/jan/30/bright-ideas-oxytocin-hormone-racism

The study found that “intergroup bias that fuels prejudice, xenophobia, and intergroup violence… which maybe modulated by brain oxytocin.” This suggests that the instinctual desire to pursue the interests of one’s own ethnic group to further ensure the existence of one’s people is linked to racial bias, coinciding with the observation that diversity is a weakness, not a strength.

http://www.pnas.org/content/early/2011/01/06/1015316108

One study found that during the menstrual cycle when women have a higher likelihood of conception, racial bias is increased, especially when the likelihood of sexual intercourse was increased; “increased conception risk was positively associated with several measures of race bias. This association was particularly strong when perceived vulnerability to sexual coercion was high.”

Although egalitarians suggest that only a racist would consider race when it comes to reproduction and mate choice, this study observed a general, innate tendency to prefer one’s own race especially when most likely to be impregnated.

http://www.cdnresearch.net/pubs/private/racebias.pdf

The Immune System: How Important Is Race?

“If Nick Glasgow were white, he would have a nearly 90 percent chance of finding a matching bone marrow donor who could cure his leukemia.”

The reason that mixed-heritage patients are so hard to match can be found in the immune system. Different races have developed certain proteins, or markers, that are part of the body’s natural defenses. These markers help the immune system determine which cells are foreign and should be rejected.

Are cells racist?

A match between two people who share more genetically in common significantly reduces the risk of the donor and recipient cells attacking each other. (READ: cells from people of two different races will attack and fight each other as though they are a virus)

The more people of different backgrounds who produce offspring = the more types that are harder to match.

Multiracial patients have uncommon profiles and since there can be many possible racial and ethnic combinations in multiracial societies, finding a match can still be extremely difficult.

http://m.phys.org/_news162659550.html

As an example, a White mother of mixed-race child would have more genetically in common with a random White person on the street than with her own child.

If such a dramatic and fundamental alienation from your own parents if not horrific enough, with a mixed-race child diagnosed with leukaemia, every member of the child’s own family becomes an incompatible donor for a bone-marrow transplant, and finding a compatible donor is unlikely.

One obstacle to finding a matching donor was her mixed ethnic background. Her father is black, with West Indian and Panamanian roots. Her mother is white, with Russian-Jewish roots. In addition, only 5 percent of registered donors are black.

http://www.nytimes.com/1996/04/18/sports/baseball-rod-carew-s-daughter-dies.html

Bone Marrow Transplants: When Race Is an Issue

”Compared to organ transplants, bone marrow donations need to be even more genetically similar to their recipients. Since all the immune system’s cells come from bone marrow, a transplant essentially introduces a new immune system to a person. Without genetic similarity between the donor and the patient, the new white blood cells will attack the host body.”

http://www.time.com/time/health/article/0,8599,1993074,00.html

Race matters when a patient needs a stem cell or marrow transplant

If you become ill with a blood cancer or other disease that requires a stem cell transplant, here’s an uncomfortable fact: Your race matters. Diversity is a strength in much of life, [citation needed!] but it’s a curse when finding a stem cell donor match.

http://articles.washingtonpost.com/2013-08-05/national/41085742_1_stem-jeffrey-chell-ancestors

The Race for Ancestral Genetics in Clinical Trials

A seasoned cancer researcher would never set up a study in which all the ill patients were, say, Canadian, and all the healthy controls were Japanese. And yet cancer researchers risk making a similar mistake if they overlook genetic information that fleshes out what many of us like to think of as race or ethnicity, some experts say.

Fortunately, awareness of how ancestral genetics might contribute to risk of disease and drug response in people has risen over the last several years. Studies that look directly at the problem are on the rapid rise, and this increased interest has biotechnology companies lowering the cost of tests that determine genetic ancestry, thanks to a little competition. However, experts have yet to decide on how to genetically define ancestry, suggesting examining anywhere from a handful to hundreds of gene variants.

Not including information on the race or ethnicity of study volunteers could skew disease risks as stronger or weaker than they really are.

“Alzheimer’s disease is the poster child for this problem,” says pharmacogeneticist Esteban Burchard, M.D., of the University of California in San Francisco. A variant of the gene ApoE4 is a strong genetic risk factor for early-onset Alzheimer’s disease, and the characteristic most likely to raise or lower that risk is race.

“It occurs in about 20% of the African American population, and it means nothing. It occurs in about 6% of the Japanese, and it makes their risk six times higher [than that for white people],” Burchard said. “Something about being Japanese unleashes the wrath of the gene, and something about being African American attenuates it.”

http://jnci.oxfordjournals.org/content/98/18/1270.full

… heart drug BiDil works only on blacks

The FDA have approved a heart failure drug called Bidil, but only for blacks, as blacks do not benefit from conventional heart failure drugs.

http://online.wsj.com/article/SB116096445875393515.html?mg=com-wsj

Sickle-Cell Disease

Sickle cell anaemia is a condition found almost exclusively in blacks. About 1 in 4 West Africans carry the gene for it, but almost no whites do. Any whites who carry the gene most likely have a black ancestor.

As a result of population growth in African-Caribbean regions of overseas France and immigration from North and sub-Saharan Africa to mainland France, sickle-cell disease has become a major health problem in France. SCD has become the most common genetic disease in this country.

https://en.wikipedia.org/wiki/Sickle_cell_anemia