Previous interpretations of oestrus swellings in baboons seem valid, but miss intriguing angles 

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Readers, please consider the following spectacle: https://www.dreamstime.com/herd-female-baboons-red-swollen-folds-skin-around-buttocks-signaling-readiness-mating-conception-large-image221295322 and https://www.dreamstime.com/large-herd-female-baboons-red-swollen-folds-skin-around-buttocks-signaling-readiness-mating-conception-image220460521 and https://es.123rf.com/photo_33721858_detail-pink-baboons.html.

Nunn (1999, http://www.sciencedirect.com/science/article/pii/S0003347299911594) has, at a certain level, nicely interpreted the function of oestrus swellings in baboons (https://catalyticcolor.com/attract-the-opposite-sex-by-wearing-this-color/female-hamadryas-baboon-in-oestrus-displaying-swelling/ and scroll in https://www.monaconatureencyclopedia.com/papio-hamadryas/?lang=en and https://www.nature.com/articles/35065597).

However, the purpose of this Post is to emphasise that

• there are also other, equally valid, levels left to discuss, and
• the extreme strategy represented by oestrus swellings (https://es.123rf.com/photo_33637580_detail-pink-baboons.html) is consistent with the theme that baboons are quasi-sociopathic.

(By 'quasi-sociopathic', I mean that, if humans functioned in this way, we would regard it as sociopathic.)

As Nunn points out:
Females manage their reproductive physiology as best they can, to get a certain result. This is one in which they achieve the best possible paternity for offspring, while at the same time protecting offspring from the quasi-sociopathic males in the group - which sometimes take infants hostage, and even kill them, for selfish, ultimately sexual reasons.
 
The system of progressive swelling on the posterior of females seems to facilitate this agenda.

This is because it ensures that, at the peak of the swelling (which is the time of ovulation, https://evostudies.org/2012/09/graded-signal-sexual-swellings-as-self-deception/baboon_in_estrus/), a given female individual is monopolised by the alpha male in its group, while also allowing many other, less successful, male individuals to mate with it, before and after this peak.

This starts with those low in the hierarchy, such as juveniles, when the swelling begins, two weeks before ovulation.

The main advantage of this promiscuity seems as follows.

Given that baboons have long memories and excellent cognition of individual interactions, every male individual that mated with a given female individual during this oestrus will remember the occasion, and harbour doubt as to the identity of the real father.

Because so many male individuals suspect that the offspring might possibly be their own, they will tend (to various degrees) to be reluctant to harm it, and may even venture to protect it.

Meanwhile, the probably successful inseminator, i.e. the alpha male at the time, will probably be the offspring’s most ardent protector.

This is often accompanied by the mother in question ‘befriending’ (if that word applies) the father after it loses alpha status.

What females really do is to manage a particular tolerance towards infants on the part of likely fathers. This needs particular management, because

• baboons behave so amorally, even in paternity, and
• it takes special measures to induce fathers to treat their own offspring well, even if they realise that these are their own offspring.

I agree with Nunn's (1999) explanation of an oestrus cycle with accompanying graded promiscuity, culminating in fertilisation by a dominant male individual.

However, what remain to be explained are

• why the oestrus swelling is so extreme (https://www.reddit.com/r/WTF/comments/1wrz1x/female_baboon_in_heat/ and https://www.dreamstime.com/baboon-monkey-sitting-showing-his-pink-butt-baboon-monkey-sitting-showing-his-pink-butt-image136997171), a figurative sledgehammer to crack a nut, given that the males involved are so acutely observant that they could track the oestrus cycle even with visual, auditory, and olfactory clues below the detection limit of most human observers, and
• why the anatomical configuration of this complex swelling seems calculated, perversely, to push the anus and vagina together even as the swelling pushes apart the ischial callosities and compromises a function as basic as sitting (https://www.dreamstime.com/baboon-monkey-sitting-showing-his-pink-butt-baboon-monkey-sitting-showing-his-pink-butt-image136997171 and scroll in https://theethogram.com/2019/02/19/creature-feature-hamadryas-baboon/).

What might seem more reasonable - in terms of hygiene - would be for this swelling to boost the distance between anus and vagina, by being centred on the skin between these two orifices.

Instead, by being centred on both the skin between anus and tail-base, and the skin of the perineum, the large swelling – with its seemingly gratuitous bumps and crannies - multiplies by orders of magnitude the normal risk of faecal contamination of the vagina (https://www.flickr.com/photos/dawvon/24684781632). 
 
My new interpretations:
 
Essentially, the male uses a ‘sledgehammer to crack a nut’ by the evolutionary adoption, as his main means of rivalry, of seemingly excessive canine teeth, of a size and kind that outdoes even Carnivora.

These teeth are used not only for mutual intimidation among the males, but also for terrorising females and juveniles.

I realise that males do not bite females or juveniles with the canines. They use the stout incisors instead, for this purpose. However, the canines are so lethal, and the males so self-centred, that a fear of the canines is never far from the mind of any individual in the societies of baboons.
 
At one level, the oestrus swelling is females' answer to this ‘sledgehammer’, their own sledgehammer to keep the power of males in check.

The masculine canines are hyperbolic, relative to the agenda at hand: masculine rivalry, an agenda common to many animals, most of which do not resort to such violent innuendo.

Similarly, the oestrus swelling is hyperbolic, adequate to the task of stimulating such amoral minds as those of baboons to behave well, reproductively.
 
Hans Kummer’s (https://de.wikipedia.org/wiki/Hans_Kummer) has used the metaphor of the Roman gladiatorial ‘sword vs the net’.

Masculinity in baboons is all about the sword, in the form of the canines. However, the way of females is the net - referring to social information or other guiles, sometimes as Machiavellian as the ways of males. In a strange way, the oestrus swelling 'nets' the males, and counters their selfish agenda without directly countering their brute force.
 
Can one truly understand the society of baboons, without understanding both these levels of interpretation?

And I remind readers that none of this would be necessary if baboons had

• as much empathy as humans, canids, and even the lion (Panthera leo) do, and
• a more considerate way of settling these matters according to the antonyms for the word ‘machiavellian’ (https://www.merriam-webster.com/thesaurus/Machiavellian).

To summarise so far:
Masculine canines and feminine oestrus swellings are what it looks like when a hypersocial primate lives in a consistently machiavellian way, in which morality is inapplicable but there is much sexual intrigue.
 
Now, to consider an interpretation of the puzzle of faecal contamination of the reproductive tracts of both female and male - and a new explanation invoking the immune system.
 
Nobody knows quite what the value of sex is in the first place, but it must have great evolutionary value to justify such nasty and brutish forms of sexism as we see in baboons.

The best explanation for sex is that it ensures that natural selection will operate on the quality of the genetic material, continually updating genetic combinations to adapt to the environmental changes at hand.

And, more particularly, it seems likely that immunity is a large part of what makes one individual superior, as a reproductive partner, over another.
 
Each individual has an individual immune profile, owing to its history of nature and nurture.

What sex seems designed to ensure is that the right partners combine gametes, making the offspring the best combination of the immune strengths of the parents. Much of the courtship behaviour of humans and other animals seems to function, at least in part, to allow prospective partners to assess each other’s immune systems.

Is it not a matter of common experience that a member of the opposite sex may look attractive, but if he or she does not smell or taste right, the dating falters because both individuals tend to lose interest?
 
Now, at the start of the oestrus swelling, the risk of faecal contamination is minor. This is because the orifices are not yet so crowded together and the crannies not so messy.

So, those low in the male hierarchy manage to mate, without deeply contaminating the female’s reproductive tract.

However, by the peak of oestrus, when an alpha male consorts exclusively for a day or two with a female individual, its intromission seems sure to inseminate and inoculate the reproductive tract simultaneously.

Why should this be evolutionarily desirable? Well, please consider this.
 
An alpha male is, by virtue of the sociopathic system of male rivalry, likely to be the strongest/fittest individual among the males at the time. So this the right mate from a conventional point of view.

However, what if the immune profile of this individual is not optimal for a given female individual? In that case, the latter has the evolutionary challenge of somehow finding a way to reject the sperm of the former, in favour of another suitor, mated either before or after it.

The reproductive tract is capacious enough to keep the sperm of various males alive, for days or possibly weeks. So, there is likely to be ‘sperm competition’ internally in the female reproductive tract.

Furthermore, an underappreciated fact is that semen, in its own right, normally contains various bacteria (https://biomed.missouri.edu/harmful-bacteria-may-hide-in-semen/ and https://www.frontiersin.org/articles/10.3389/fmicb.2019.00234/full and https://www.thepigsite.com/genetics-and-reproduction/insemination/facts-about-semen).

My hypothesis is that the presence of faecal matter, belonging to females, somehow facilitates the contest of male immunities. This would ensure that, if an alpha male is not the best immune-match for a given female, another male will succeed in fertilisation.

This other male may be suboptimal in terms of its position in the hierarchy, but optimal in terms of its immune profile.

Such competition within the tract could theoretically occur in the absence of faecal contamination. However, can readers think of a physiological mechanism whereby the inoculation with bacteria and other factors present in faeces would somehow facilitate this seminal contest?

Auto-immune syndromes may possibly provide clues. A puzzling reality is that the body sometimes ‘fights itself’.

Perhaps the faecal contamination is a form of ‘fighting itself’. In this case, the bacteria from the colon are ‘fighting’ the seminal microbes. They will prey on them in essence. Could it be that sperm that survive this conflict are most likely to be the ‘best fit’ for the female?

It seems to be a plausible idea that the anatomy of the reproductive tract tests the seminal quality of most of the males that copulate with a given female during a given cycle of oestrus. The earlier males, i.e. low in the hierarchy, will introduce their sperm to the female reproductive tract, before faecal contamination is likely. However, these sperm will have to wait until ovulation occurs.

An alpha-male will have the advantage of inseminating the tract right at the time of ovulation. However, it will have the handicap of being maximally challenged by faecal microbes.

All the sperm that survive in the tract will have to have run a gauntlet, i.e. a certain ‘inoculation challenge’, of faecal microbes, by the time fertilisation is possible.

Perhaps one can partly envisage these matters as follows.

The body contains essentially two compartments of life, viz.

• the macrobial compartment, with which most of us identify ourselves, and
• the microbial compartment, consisting mainly of our gut microbes (https://www.hopkinsmedicine.org/research/advancements-in-research/fundamentals/in-depth/the-gut-where-bacteria-and-immune-system-meet and https://www.immunology.org/public-information/bitesized-immunology/organs-and-tissues/immunity-in-the-gut and https://en.wikipedia.org/wiki/Microbial_symbiosis_and_immunity).

Both compartments are part of the immune system. The gut microbiome has its own intelligence and its own nervous system - which is possibly why antibiotics taken orally can be so debilitating to the immune system.

Normally the partnership between macrobe and microbe works well enough, with a certain compartmentalisation in which the microbiome is confined spatially. However, in sex the whole idea is to do as much as possible to test the individual and contingent immune systems, to establish maximum fitness at the moment in question.

This can be achieved by creating a tract in which MACROBIOME AND MICROBIOME are mixed up and shaken, as it were.

Sperm are essentially the closest thing to free-living microbes that the macrobial cells produce. Therefore, the testing follows from the ‘co-inoculation’ of the female tract with

• sperm,
• microbes introduced via semen, and
• microbes introduced via faeces.

Perhaps a search of the literature will show papers discussing the faecal messing of the vulva in monkeys. However, such messing is obvious from photos. Have the minds of experienced and deep-thinking primatologists possibly recoiled from this phenomenon, to the degree of avoiding the topic?

How likely is it that so many researchers, watching monkeys come into oestrus repeatedly in long-term field studies in which the scientists walk and sit mere inches from their study subjects, would not have noticed the faecal contamination?

Publicado el julio 20, 2022 10:22 TARDE por milewski