Mating

       We are all acquainted with what mating involves in humans. Whether it be a physical, emotional, sexual, or all of them, we have a good idea of what it consists of. But what of non-human primates? In the following blog I will address the selection of a mate, the subject of infants, and of “families” in non-human primates.
      As humans, we are not attracted to other species, such as chimpanzee's or the like; sure, we think they are cute, but not “mate” material. But for the females of the different species of ape, some have a choice with whom to mate with. For most of them there is a polygynous system, in which there is one male mating with several females. In a previous blog (http://anthropologicalconcepts.weebly.com/blog/sexual-dimorphism), I discussed sexual
dimorphism; in those in which there was a great deal of sexual dimorphism, there is a competition. It is usually the one with the most evident sexual dimorphism that is able to mate. Although, in those who do not have great sexual dimorphism, they usually live in pairs while the child is being weened. Some of those are monogamous, some also mate with other females, but for those they will stay with the female they impregnated. “Primates are amoung the most K-selected of mammal species.” K-selected means that they produce a low number of offspring so as to invest more time with the one child (the opposite is r-selected in which a large number of offspring are produced). With female primates, they spend most of their adult life “being pregnant, lactating, and/or caring for offspring.” For Old World apes their genitals swell and change colour, so in some they do no have a choice.
       In some males, since they do not have invest in rearing the offspring, the want to produce as many offspring as they can; which is sometimes dangerous...to the offspring. What I mean by this is if another male becomes the leader of the pack, they will commit infanticide with the offspring that is not theirs. Even though this is highly counter-productive for the species, the males “need” to do this. Reason being is while the mother is lactating and caring for her offspring, she does not come into estrus (heat), and therefore is not sexually available. So the new male in charge kills the offspring, so that he only has to wait two to three months, and not two to three years to mate with the females. In chacma baboons, for example, they “deliberately single out females with young infants and hunt them down (image below).” All that said, it does not prove the male's reproductive fitness. What primatologists look for are two crucial facts:

1. Infanticidal males don't kill their own offspring,
2. Once a male has killed an infant, he subsequently father another infant with the victim's mother.

But chacma baboons are not the only species in which the males practice infanticide; others include Hanuman langurs, redtail monkeys, red colobus, blue monkeys, howlers, orangutans, gorillas, chimpanzees, and, sadly, humans. 

       But it is not all bad news for the infants for one reason, their mothers. Not counting those communities with polyandry (female with many males mates where the males is in charge of rearing the offspring), the bond between primate mothers and their infants begins at birth. We are not sure what the bonding process is, but if the mother had a normal experience with hers, it is evident early. In other cases were the female was raised in captivity without knowing their mother, she will most likely be afraid of her offspring, or kill it. Although, when the female has had a normal relationship with her mother, she knows what to do. As for the infant, it is as if it is automatic, as they grasp onto their mothers fur, and are in this constant contact for several months (which gives you an idea why some males would commit infanticide). While in this contact, they are exposed to social behaviour. In many primate communities they allow alloparenting, which is when those who are not the parents of said infant carry, hold, and just interact with them. But the mother has to be careful because there have been instances of the death or injury of the infant due to the inexperience or aggressiveness. This alloparenting is very useful just in case the mother dies or is unable to take care of her infant. Amoung the siamangs, marmosets, and tamarins, the males are actively involved. And in the case of marmosets and tamarins, the infants are frequently twins, so the father carries them on his back and are only away from him when nursing with their mother.. Even in those species where they do not actively involved, the exhibit paternal care. For example, “they showed that during disputes, the fathers intervened on behalf of their offspring significantly more often that for unrelated juveniles.”
       This interaction with not only their mothers, but with their “aunts” is very important for not only the infant but those females who have yet to give birth. Being with those infants is a way for them to learn what to do. But, in the case of infants who have undergone social isolation, it is obvious they need it. They have been recorded displaying self-direct behaviour, such as hugging themselves or rocking back and forth. For the social group in these primates it is suggested that the mother-offspring core gives it stability.
​       Please feel free to comment on what you thought of the blog, or other physical anthropological subjects you would like me to cover.

Images above from left to right: Patas monkey, Mongoose Lemur, Orangutan, Chimpanzee, Sykes monkey
Click to image to make bigger.