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#sajsci all right! @treestargarden asked about whether people experience heightened romantic attraction towards those who have complementary immune systems, so today I am going to talk about the evidence for/against this idea (1/16)
#sajsci first off, let’s talk about what “complementary immune systems” means. this has to do with something called the major histocompatibility complex gene (MHC). the MHC I protein helps immune cells differentiate between “self” and “foreign” cells. (2/16)
#sajsci think of it this way. immune cells are like the police. they knock on the door to see whether a cell contains “self” or “foreign” substances. MHC I is the protein that answers the door and shows the immune cell what’s inside. (3/16)
#sajsci now, there are many different types of MHCs, and each person’s genes code for a certain set of MHCs. in other words, I might have the red, yellow, and green MHCs, but you might have the red, purple, and orange MHCs. (note: they aren’t actually colored). (4/16)
#sajsci each MHC type can only show the immune cell a certain set of proteins. so, the immune cell knocks on the door, the MHC shows the immune cell a few proteins, and if the MHC presents a foreign substance to the immune cell, that activates the immune response. (5/16)
#sajsci the more diverse your collection of MHCs, the wider the selection of proteins your MHCs can present to immune cells. this increases the chance that your immune cells will recognize a virus. (6/16)
#sajsci if you have the red, purple, and orange MHCs, and a virus produces orange proteins, your MHCs will show the immune cell the orange protein, and all is good. but if a virus produces yellow, your MHCs won’t be able to tell the immune cell that the virus is there. (7/16)
#sajsci so, people with more diverse MHCs are at an advantage. and you inherit your MHCs from your parents, so if your parents have highly similar MHCs, you will inherit a less diverse set of MHCs, and that will give you a disadvantage in terms of survival. (8/16)
#sajsci to keep running w the color metaphor, if your parents both have red and yellow MHCs, and you only inherit one MHC from both of them, there is a chance you could inherit two red MHCs, and that's pretty unfortunate! (9/16)
#sajsci on the other hand, if your parents have completely different sets of MHCs--say one parent has red and yellow and one parent has orange and purple--you are guaranteed to inherit two different colored MHCs. (10/16)
#sajsci that means, evolutionarily speaking, that if you want to give your kid a leg up, you want to mate with someone who has different MHCs from you. for this reason, most animals show a preference for the odors of animals who have different MHCs from them! (11/16)
#sajsci so do humans actually show a romantic preference for people with different MHCs from their own? the evidence on that is mixed at best. apparently, we prefer the body odors of people with different MHCs from us, and many married couples have different sets of MHCs. (12/16)
#sajsci but we find face-shapes of people with more similar MHCs more attractive. to make things more complicated, MHCs seem to be important to women than men when selecting a partner. (13/16)
#sajsci even weirder, apparently women who are on birth control prefer odors of men with MHCs that more closely match their own. this is the *opposite* of what was found for women who aren’t on birth control. (14/16)
#sajsci so there you have it! there is some evidence that we select partners based on how well their immune system complements our own, but more research is needed before we can reasonably say anything. (15/16)
#sajsci and here is the abstract for the article I read while making this thread (the full article is behind a paywall, but if you are in uni, your uni might have access): https://www.sciencedirect.com/science/article/abs/pii/S0306453008002667 (16/16)
