Why did we lose our fur?

[WoodDragon]

And yeah, smell is SO important in mate selection. I know that it makes or breaks it for me, even when all other factors would seem to be perfect and even though I don't have a good olfactory sense.

It's also why we wear perfumes - humans recognise (often unconsciously) that their own smell might dissuade a prospective partner, and if that partner is a desirable mate then disguising a pheromonal smell that is unappealing to that prospective partner is a good strategy. (It also helps to deal with smells that arise from poor health - another prospective partner turn-off.)

Smell is also why the contraceptive pill is such a bugger for mate selection. Women are generally naturally pheromonally-attracted to men who have an appreciably different Human Leucocyte Antigen profile to their own, which helps to prevent inbreeding. Once they become pregnant, women are more attracted to men whose smell reflects a related HLA type - this helps to keep her from seeking out men who are not related, and to stay closer to men who are related. It's no surprise that in pre-'civilisation' times (and perhaps even now) males had a tendency to kill infants who they did not father, and to protect the infants of women to whom they were related - so this pheromone switch in the men that pregnant women are drawn to makes sense.

The thing is, the pill works by mimicking pregnancy in the female body - this mimicry is what stops ovulation from happening. The trouble happens because this mimicry also tends to invert the HLA type of men that women are attracted to... As a consequence women on the pill, who are also dating, seem to select more closely HLA-related men than they naturally would, which means that when they go off the pill to get pregnant, they may:

1) have less overall HLA diversity in their children, compared to women not taking the pill when they choose a mate, and

2) suddenly find themselves less attracted to their partners once they stop using hormonal contraception

I wouldn't be surprised if, in an other decade or two, a large study of human relationships finds that late 20th century/ early 21st century human genetic- and relationship-health in modern societies have been noticably compromised by the use of the contraceptive pill.

Edited June 4, 2011 by WoodDragon

[tripsis]

By fired up the 'wrong way', you mean that the woman's immune system is simply overreacting and is wiping out the sperm before it gets an opportunity to fertilise the egg?

[WoodDragon]

By fired up the 'wrong way', you mean that the woman's immune system is simply overreacting and is wiping out the sperm before it gets an opportunity to fertilise the egg?

Yeah, basically.

Developing, in early life, a suite of immune responses to non-self antigens is a complicated business, and by adulthood there is almost always an element of recognition of a male's personal antigens as being foreign to a female, but usually the development of this recognition occurs at a level that doesn't prevent conception or pregnancy. This sort of immune recognition is natural, and not pathological.

Sometimes, though, the immunisation history of a woman (types of food she ate, her parasitic load, the timing of exposure to various foreign substances, what diseases she's had) just add up in a way that means she develops an unnecessarily vigorous response to male sperm, or perhaps just to an individual male's sperm. This might manifest as infertility with no other signs or symptoms on the one hand, to an extreme (and in some cases life-threateningly allergic) response to semen on the other.

If it's just a matter of a bit of a dodgy immune history, then an immune infertility may be fixed by the desensitising 'reset' procedure I described above, just as clinicians can do with over-reactivity to bees, ants, nuts and other substances. It's important to note that a sperm immunity may not be an allergy per se, although sometimes it can be, but that it may still be sufficiently vigorous that conception and/or pregnancy are not easy to achieve.

[tripsis]

Really, an allergy to semen? I suppose it shouldn't surprise me, but I've not heard of that one before. Is it an allergy to the proteins, or something else?

[WoodDragon]

Yep, protein, or glycoprotein. It's a well recognised allergy, if not a very common one.

More info here, and here.

[tripsis]

Thanks for the links, it's really quite fascinating. Such an unusual allergy to have, especially in its more severe forms. Under natural circumstances, it seems like it would be bound to be selected against.

I found this quite interesting:

Scientists at Utrecht University studied the condition whereby some men "get flu-like symptoms such as feverishness, runny nose, extreme fatigue and burning eyes immediately after they ejaculate. Symptoms can last for up to week."[21] This condition is termed post orgasmic illness syndrome or POIS, and it was discovered that this stemmed from an allergy to their own semen, its effects could be cured using hyposensitization therapy or allergen immunotherapy.[21]

Any idea what woud cause it?

Also this:

However, this allergy can be very disruptive to interpersonal relationships. “I have seen people who have gone on to find different partners because the allergy was unique to the individual that they were with,” says Bernstein.

That's like being allergy to only almonds from a particular tree!

[WoodDragon]

Any idea what woud cause it?

It's basically an autoimmunity like diabetes, or multiple sclerosis, or lupus, or any number of other diseases.

In the case of semen autoimmunity it would seem to me that as long as the sperm/fluid remains in the testes/epididymis/prostate (as the case may be), there is no reaction. This probably reflects the fact that the required antigen-presenting cells and/or other co-effector cells, needed to kick off an immune response, might not be as common in these organs as they are elsewhere.

As to the initial cause for the overall sperm autoimmunity, it could be genetic, or viral cross-reactivity, or viral alteration of other immune responses, or a non-'natural' history of immune challenge. It would be hard to say for any particular case, using current techniques available to medicine.

[The Dude]

 

http://www.youtube.com/watch?v=qNGngZsxAhw

[WoodDragon]

 

This Lloyd Pye?

[ThunderIdeal]

i have only half read the wiki article, but i've watched the series dude posted (the bottom video is part 1). i am an open-minded, undecided sort, but i have an inclination to entertain ideas like these. i am impressed by his presentation.