Sweath t-shirt study
Overview of the 1995 sweaty T-shirt study: women smelled T-shirts worn by different men, for several days, and picked the ones they were most sexually attracted to; the men and women were then DNA typed, and the attraction patterns indicated that women tended to choose the scents of the men they were most MHC complex dissimilar to.
In studies, sweaty T-shirt study is a mate selection study, conducted in 1995 by Swiss biologist Claus Wedekind, based on earlier animal studies, which found that people are most attracted to the scent of someone of the opposite sex that has the most dissimilar immune system to their own. [1] The results of the sweaty T-shirt study were used, at one point, by the once-active science-based pair matching site ScienticMatch.com (2008) to match people. [2] American anthropologist Helen Fisher calls the sweaty T-shirt study "one of the most important modern scientific studies". [3]

In the mid 1970s, MHC-dissimilar tendency matching was shown to be the case for mice (and later for other animals such as fish).

In 1974, the writer and medical researcher Lewis Thomas suggested that different MHC genes might be linked to different odors. He was considering training dogs to sniff out compatible people for skin grafts and organ donations. That led to work on laboratory mice and rats that established that the animals preferred mates that were different in their MHC genes.

Laboratory studies soon proved Thomas right in the case of mice. Inbred mice, who were alike in all genes but MHC, could detect a difference in the scent of a relative that harbored an ever-so-slightly different MHC gene. Moreover, their odor preferences were not innate but learned. Young mice tend to prefer the odor of their nest mates, but when they hit puberty: they preferred to mate with mice whose MHC genes were unlike their own. [4]

Scientists speculated that this was either a mechanism to prevent inbreeding or a way for animals to insure that their offspring would have immune systems diverse enough to fight as many diseases as possible. [5]

In 1995,
Swiss biologist Claus Wedekind, based on the previous animal studies, tested the theory on humans. In this study, Wedekind had a group of female college students smell T-shirts that had been worn by male students for three nights, without deodorant, cologne or scented soaps. Overwhelmingly, the women preferred the odors of men with the most dissimilar MHCs to their own

The theory of desired dissimilar immune system matching can be quantified according to markers on a person’s major histocompatibility complex (MHC), a large gene region that controls the immune system response, and postulates that couples attracted to this type of scent owing to the result that a resultant child would create a more robust immune system, more defensive against a greater variety of pathogens.

Wedekind, in particular, recruited a group of 49 women and 44 men who harbored a wide range of MHC genes. Wedekind gave each man a clean T-shirt on a Sunday morning and asked him to wear it for two nights. [4] He decided to gather male scent rather than female scent simply because unshaved armpits collect more odor. In fact, to ensure a strong body odor, he gave the men supplies of odor-free soap and aftershave and asked them to remain as "odor neutral" as possible.

On Tuesday morning, the men returned, sweaty T-shirts in hand. Wedekind put each shirt in a plastic-lined cardboard box with a sniffing hole on top. Then he brought in the women. Each was scheduled for the experiment at the midpoint of her menstrual cycle, when women's noses are reputedly the keenest, and each was presented with a different set of seven boxes. Three of the seven boxes contained T-shirts from men harboring MHC similar to the woman's own; three contained T-shirts from MHC-dissimilar men; and one contained an unworn T-shirt as a control.

The women were asked to rate each of the seven T-shirts as pleasant or unpleasant. Overall, says Wedekind, the women he tested were more likely to prefer the scent of men with dissimilar MHC. In fact, that scent tended to remind them of their boyfriends, both past and present. Says Wedekind, "This is the first indication that MHC still plays a role in mate choice today."
15 degree rule
A 2015 snippet (ΡΊ) on Libb Thims 2003 study, on mate selection preferences in respect to MHC matching optimization, which found the 15 degree rule, i.e. in opposition to inbreeding, people tend to be most sexually attracted to people who are above them, in genetic composition, by plus or minus 15 degrees in latitude, according to polled opinion.

15 degree rule
In 2003, American electrochemical engineer Libb Thims conducted a study of 83 individuals, based on the findings of the MHC sent attraction studies, wherein, knowing that each MHC profile, per person, is based on one’s average ethnicity, i.e. the latitudes of existence of the ancestors of each individual person, in the sense that each latitude will tend to yield species that survive owing to certain disease susceptibility trait resistances, he polled each person as to what (a) ethnicity they were most sexually-attracted to and (b) their own ethnicity. The results of the study found that people, on average, were least sexually attracted to individuals of their own latitude of ethnicity, something already known from the Claus Wedekind (1995) study, and “most” sexually-attracted to individuals ±15° in latitude, above or below their own latitude of ethnicity. [6] This has since been referred to as the 15 degree rule of mate selection, in regards to physical traits attraction compatibilities.

A video documentary on the sweaty T-shirt study.
Science-based dating sites
Two science-based dating sites structured around MHC-matching theory include the 2003-launched GenePartner.com, the 2007-launched ScientificMatch.com.

1. Wedekind, Claus, Seebeck, Thomas, Bettens, Florence, and Paepke, Alexander J. (1995). “MHC-Dependent Preferences in Humans." Proceedings of the Royal Society of London 260: 245-49.
2. ScientificMatch.com - homepage.
3. Corcoran, David. (2007). "Helen Fisher Talks About the Sweaty T-Shirt Experiment" (YouTube). New York Times (Science), On Desire: with David Corcoran and Helen Fisher, 10 April.
4. Richardson, Sarah. (1996). “Scent of a Man”, Discover Magazine, Feb.
5. Berreby, David. (1998). “Studies Explore Love and the Sweaty T-Shirt”, The New York Times, Jun 09.
6. (a) Thims, Libb. (2003). “Optimal Ethnic (Latitude) Separation vs. Maximal Attraction” (N=83). Chicago: Institute of Human Thermodynamics.
(b) Thims, Libb. (2007). Human Chemistry (Volume One) (pg. 272). Morrisville, NC: LuLu.
(c) Thims, Libb. (2007). Human Chemistry (Volume Two) (pg. 745). Morrisville, NC: LuLu.

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