Worthwhile illustration of sexual mimicry in the gelada

See Theropithecus gelada adult female in oestrus (left) and adult male: http://1.bp.blogspot.com/_pRrgVOeyl_Q/SR3rtW2oXEI/AAAAAAAABfg/NhyTQ4whWgY/s320/GeladaBaboonSwelling(M%26F).jpg

One of the distinctive features of the human species (Homo sapiens) is that the breasts of the adult female have been converted into sex organs.

What I mean by this is not that the female breasts in humans are exclusively sex organs; of course they retain their mammary function in motherhood. However, they DOUBLE as sex organs, as we can easily discern from

• the privacy with which they are covered by clothing in most cultures, and
• the fact that sexual stimulation of the breasts is extremely arousing in many individuals, i.e. an extremely effective form of foreplay by the courting male.

I cannot think of many other mammals in which the organ of lactation doubles as a sex organ. However, the gelada is an exception. In this way the gelada is convergent with humans. Although this fact is well-known, it is seldom stated clearly.
 
What is interesting is that the morphological accentuation of the breasts is quite different in human and gelada.

In the human species, the accentuation is mainly by permanent adiposity, without particular colouration and without much change during the oestrus cycle (although the breasts may swell to a small degree during menstruation, and I suspect that this is partly oedematous because it surely cannot reflect a short-term change in the amount of adipose tissue).

In the gelada, there is no role played by adiposity. Instead the emphasis is on colouration, the nipples being particularly intense in hue in oestrus.

Furthermore, there is an oestrus cycle, in which the border of an hourglass-shaped bare patch on the chest becomes adorned with remarkable fluid-filled vesicles. These are, in their own way, are as bizarre as the oestrus swellings on the posterior in the genus Papio.
 
It is, of course, well-known that the male gelada exhibits sexual mimicry of the breast display of the female. However, what I have not seen clearly stated in the literature is that this means, in a way, that the male gelada has converted its breasts into sex organs.

This conversion seems to be purely visual, because I know of no tactile stimulation of the breast by the female (although of course this is possible during grooming). But even if the sexual function of the male breasts in the gelada is purely a matter of visual stimulation, it might qualify as a case of breasts functioning as sex organs if the female responds sexually to the display.

If so, I cannot think if any other mammal on Earth in which the male breasts function as a sex organ.
 
I realise that a major function of this sexual mimicry by the male may possibly be appeasement among males in macho rivalry. I.e. it may be mainly other male individuals that a male individual displays to, in a way analogous to the posterior display in the male hamadryas baboon. There are many facts that need to be clearly examined about the behaviour of the gelada before we can sort out this tangle.
 
I also realise that the nipples are not noticeable in the display of the breasts of the male. However, it is unclear whether this weakens or strengthens the case that the male breasts have a sexual significance.
 
A relatively shallow explanation given in the literature is that both humans and the gelada tend to have upright postures in which the genitals tend to be hidden. In the human case this is owing to upright bipedalism, whereas in the case of the gelada it is owing to specialisation for an unique mode of locomotion while sitting on the ischial and perineal callosities.

However, this explains the visual emphasis of the breasts in the female more than it explains that in the male. This is because one has to ask why the male emphasises any part of his anatomy, other than penis and scrotum, in a sexual or macho context, with a pink hue similar to that of the female in oestrus.
  
The gelada could hardly be simpler from an ecological/trophic point of view, being THE grazer par excellence among primates. Its foraging behaviour is so simple that it verges on the monotonous.

So, the extreme social complexity of the gelada stands at odds with the simplicity of both foraging strategy and anti-predator strategy.

Itis easy to accept that, being perhaps the most terrestrial of all non-human primates, the gelada needs to be gregarious – even extremely gregarious – in order to survive predatory pressures. But this, on its own, fails to explain the extreme social complexity which occurs in the gelada, which is similar in principle to that in Papio although different in details.
 
To the extent that the social behaviour of the gelada resembles that of Papio, I suppose that the sexual displays of the gelada are, like those of Papio, ultimately designed to promote an agenda of natural selection for immunity vs microbes. But how would the breast aid this, and how does sexual mimicry of the breast contribute?

Publicado el julio 18, 2022 06:17 MAÑANA por milewski