Continuing on male-female relations, we're going to see two extremes; today we'll see female dominance, and next time male coercion. This is building on the theme developed in ch. 8 in Krebs and Davies.
Examples of species with male dominance: brown capuchins, baboons, langurs, orangutans, chimps.
All early studies in primatology focused on male dominance. One reason is that it's more visible and exciting. Also, they were all men and probably had a cultural bias that made it easier for them to see the male dominance. After a while, though, they began to see that females formed social bonds and could gang up on males. Through the 80's all serious work on female dominance was done by women primatologists.
"To a greater or lesser extent, females in these species take priority at feeding sites and control social access to other group members. An offending male who comes too close to a female or her infant is cuffed in the face or chased away, and in some cases males are relegated tot eh outskirts of the troops. These species stand in contrast to television narratives about 'central male hierarchies' and 'dominant male leaders' - Sarah Hrdy 1981, pg 59, describing female dominance
Most female dominance species are in the prosimians, especially the prosimians of Madagascar. Ring-tailed lemur, sifakas (propithecus), and the indriis who are monogamous.
There are also a few cases outside of Madagascar; squirrel monkey (evidence not quite so clear cut), and the talapon which is a small cercopithecus. In apes, some newer research on bonobos shows that by forming alliances with each other, the females are able to socially dominate the males.
For a while it looked like the whole lemuridae family was female dominant, but it turned out that that's not the case- a 1990 comparative study of ring-tailed lemurs, crowned lemurs, and brown lemurs found that females were dominant in the ring tailed and the crowned lemur, but not in the brown lemur. Therefore, we can't just write it off as a characteristic of lemurs.
|The male perspective|
|Males defer to females in order to conserve
energy for the brief, but energetically costly, annual mating season.
Think about it- male competition is all about mating access, but if for most of the time there are no receptive females since the breeding system is so short, then what's the point of wasting energy being dominant?
|The female perspective|
|Environmental or metabolic factors combine to increase the costs of reproduction for females. Given these circumstances, females win competitive interactions because the benefits they gain are greater than those derived by males. Basically, females are harder-pressed to get enough food.|
She collected data over 2 year period based on focal samples of females who were pregnant or lactating- in other words, not attractive to males. She found that the non-estrous female was attacked once a week. This usually didn't involve biting, but there is always that potential. A female typically got a serious wound once a year- including a slash with canines that will draw blood. A slash is generally not too awful, but it does interfere with foraging and mothering. Only once did she see a fatal attack and she doesn't think the male intended to kill the female.
She thinks that in some cases the male was punishing the female for something she did several hours or several days earlier. Why does she think this? Once she saw a female attack another female who was a friend of a male. Smuts watched the male, and when the attacking female returned, he attacked her. So many of these 'unprovoked' cases might involve earlier incidents which hadn't been seen by the observer. In other cases, she thinks that it's just the male displaying his superiority over the female and reminding her of his power over her so when he tried to mate later, she would be more likely to submit to him.
|Review on male-male competition and female mate choice|
|The main way males can increase their mating success is by fighting with each for mating. Fighting establishes a mating hierarchy where the higher-ranking males have more access to females when the females are likely to be fertile. When you think about it, the outcome of male-male competition doesn't guarantee mating access- one way it does is if females prefer to mate with dominant males. This is apparent in many species including savannah baboons. They might pick dominant males 'cause they have better genes or because they can protect them better, being stronger.|
Another way for the males to increase their mating success is by inflicting costs onto the females if they don't cooperate- this is an alternative to providing benefits. A primary way to inflict costs is by threats or actual aggression.
Definition: Any use of force or threatened use of force by a male against a female that functions to increase that male's mating access to the female, or that functions to decrease the probability that she will mate with another male, or both.
Rhesus macaques- Joe Manson did a study on their mating behavior and found a high incidence of male aggression. When a female is mating with a low-ranking male, a high-ranking male is likely to come along and attack and chase the female, not the other male. Smuts spent a few weeks with this population when she was thinking about this subject, and was really struck by how much violence there was. What Manson points out is that even though females pay this cost, they continue to solicit low-ranking males. So here, female choice is coming into conflict with male mating strategies.
Chimps- Jane Goodall has provided data on how often male aggression occurs in chimps. It's most common against estrous females- for instance a picture shown in lecture which shows a male who has lifted a female up and is biting her on the back of the leg.
Goodall has a detailed analysis with good data and she noted a few things- a lot of male aggression against female chimps occurred in the first few days of their estrous cycle, before swelling. A female chimp swells for a few weeks and ovulates at the end, but most aggression is at beginning of swelling- it seems that males attack females repeatedly during their first phase to condition them to sexual submission so that as she reaches ovulation, she's more likely to submit to the advances of the male who attacked her. This is mostly based on circumstantial evidence. However, females usually don't reject sexual advances. The best strategy for male to get good mating success is to convince (read: coerce) a female to go away with him and mate in peace. The alpha male doesn't have to do this because he can keep the others away, but lower guys need to, otherwise they'll get interrupted. Some females go with guys they like but others are kept there by coercion. If she tries to leave, he bites her and things like that. So this aggression occurs hours or days before the actual mating- it's not as immediate as in the rhesus.
Hamadryas baboons- Female remain with males year after year throughout pregnancy lactation etc. This lack of association with any other males is maintained by the male hour by hour with instant reaction if the female strays too far away from the male. If a female moves too far off, the male gives the eyelid flash. If she doesn't come back, he rushes over and grabs her and gives her a ritualized bite on the back of the neck. Then she comes rushing back and presents to him (a form of ritualized submission). When she comes into estrous again, she is deeply conditioned to submit to this male after all these attacks.
Orangutans- As she said earlier, forced copulation is rare in nonhuman primates- the only species it's been documented in often in the wild is the orangutan. Remember that they're solitary females with ranges, and males who have larger ranges covering several females. When a female first comes into estrous, younger males who normally wouldn't have a chance later in the estrous cycle follow her around and force copulation. Observers know it's forced because the females scream and struggle.
(Chimps also force copulations infrequently, but it's just been seen in certain individuals in Gombe.)
Female-female coalitions against males are not found only in primates. Lions form female bonded groups and if male lions show aggression, especially toward the infants when they've just joined a group, the females band together against him. They showed that the number of females in a pride affects the number of babies that are killed when a new male moves in.
This strategy of affiliating with the male is most developed in the mountain gorilla. Females are not bonded or closely related. They don't bond with each other, but just with the male. Wrangham proposed that females do this to protect themselves against male harassment- more because of infanticide than sexual coercion but if you think about it, infanticide functions just like coercion because it brings the female into estrous sooner and increases the male's mating opportunity.
In 20 documented cases where the male gorilla died or disappeared and left females and babies, in every case all the babies were killed by another male.
Orangutans are good studies because they're the only nonhuman primate where forced copulations happen and also females travel alone- they have no other females to ally with, and no males to defend them. Smuts thinks this is why they're coerced; they have no protection.
Further evidence comes from a comparison of chimps and pygmy chimps, and
exemplifies why social organization is an important factor.
Chimps are male-bonded. The males form coalitions against males from neighboring communities. Males groom frequently, and they reconcile one another after a fight much more than females do. The closest bond in chimps is males. Females are like 85% the size of males- large females are about the size of small males, and males' teeth aren't that much larger, so sexual dimorphism doesn't do much to explain male dominance over females. However, females invariably pant grunt to males and they don't fight back when males attack them. (Signs of submission)
Contrast with this the pygmy chimps. They also have a social system where males stay and females disperse. They show just as much sexual dimorphism. Within groups, however, social relations are really different. The closest bonds by far are among adult females who are unrelated. Not only do they spend more time together and groom each other, but they have frequent intense sexual interactions. This is called GG rubbing, and it's when females rub their sexual swellings together. Researchers are pretty sure that the females reach orgasm in these homosexual relations as well as their heterosexual ones. This behavior is common in the wild; when they find a tree, before they eat, they all have sex together and then eat. It has been hypothesized that this sex is to keep the bonds close so that females can dominate the males. It has been particularly documented by Amy Parrish, studying bonobos in captivity. In 100s of hours, she never saw male aggression on females, but repeatedly saw females attacking males or inflicting wounds on them. No one has ever seen male coercion in bonobos.
So, the bonding and coalitions between females function to shift the balance of power, protecting them against male coercion.
She has found some social variables that might correlate. The Yanamano people are some of the most aggressive primitive people. They are patrilineal and people have documented very severe incidents of male aggression against females, usually because of suspected adultery.
Contrast a society of pygmies in central Africa. They're traditional hunter/gatherers where men and women gather together and the males do a lot of child-care, more than in many 'advanced' societies. Anthropologists have never seen a man lift a hand against a woman in this culture.
This comparative perspective can help us think about such a difficult issue as sexual coercion in humans and it's not a case of 'oh it's built in and males are just going to do it.' We should pay attention instead to how social bonds affect things.
We've touched on some things about adult-infant contacts; remember
Hamilton's rule: rB>C. This is the basic theoretical framework for
understanding why an adult should ever take care of any infant. We've
also seen how maximizing inclusive fitness explains males taking care of
infants in cooperative polyandry, we've also seen male relations with
infants in baboons- part of mating effort really, not parenting effort.
We've also spoken of adult females and infants in the context of
Permissive mothers stop following their infants earlier than restrictive
mothers. Early in life, mom is responsible for keeping the pair together,
but later on the infant maintains responsibility. Permissive mothers stop
following their kids at around 1mo vs. 3.25 months for the restrictive
mothers. (This is using the Heinz index of approaches vs leaves to
determine who is doing the work of maintaining the proximity.)
Anything else you look at, such as rejection of nursing or refusals to
carry, happens earlier in permissive mothers than in restrictive
Some evidence suggests that restrictive motherhood increases infant
survival. Ill health and infant death occurred at a slightly higher rate
among infants of permissive mothers (5 of 7; 71%) than among those of
restrictive mothers (2 of 5; 40%). Note from the small sample sizes that
these aren't statistically significant.
So, given a choice of mothering style, why would mothers pick a more
permissive mothering style if it increases their kids' mortality? We'll
devote a whole lecture to this in the lecture on parent-offspring
conflict, later on.
This was first documented in barbary macaques. They're noted for males
doing a lot of infant carrying and holding, but it was particularly Deag
and Crook who noticed that males were particularly likely to pick up and
carry a baby when they were in a conflict with another male. There are
two hypotheses to explain this behavior.
Another prediction is that the male who is the recipient of the behavior
(i.e. the one who is not carrying the infant) should be the father of the
infant- the infant is being used like a hostage against him- but no one
has found evidence of this.
So, a correlation has been shown, but causation has not. In other words,
maybe because he is holding infant he is not attacked, but it also could
be that when he is holding the infant, he is trying harder not to provoke
an attack since he is supposed to be protecting it.
Adult males and infants
In a lot of species there 's a lot of interactions between males and
infants in some species. These are categorized as:
A controversial aspect of male relations with infants- Triadic
This is when there are three parties involved; two adult males and one
baby. When there is a conflict between two males, sometimes one of them
will pick up an infant.
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Today we turned in a paper, got back a paper, got a take-home quiz, and reviewed the previous three lectures.
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Last modified: November, 1996
Permissive mothers stop following their infants earlier than restrictive mothers. Early in life, mom is responsible for keeping the pair together, but later on the infant maintains responsibility. Permissive mothers stop following their kids at around 1mo vs. 3.25 months for the restrictive mothers. (This is using the Heinz index of approaches vs leaves to determine who is doing the work of maintaining the proximity.)
Anything else you look at, such as rejection of nursing or refusals to carry, happens earlier in permissive mothers than in restrictive mothers.
Some evidence suggests that restrictive motherhood increases infant survival. Ill health and infant death occurred at a slightly higher rate among infants of permissive mothers (5 of 7; 71%) than among those of restrictive mothers (2 of 5; 40%). Note from the small sample sizes that these aren't statistically significant.
So, given a choice of mothering style, why would mothers pick a more permissive mothering style if it increases their kids' mortality? We'll devote a whole lecture to this in the lecture on parent-offspring conflict, later on.
This was first documented in barbary macaques. They're noted for males doing a lot of infant carrying and holding, but it was particularly Deag and Crook who noticed that males were particularly likely to pick up and carry a baby when they were in a conflict with another male. There are two hypotheses to explain this behavior.
Another prediction is that the male who is the recipient of the behavior (i.e. the one who is not carrying the infant) should be the father of the infant- the infant is being used like a hostage against him- but no one has found evidence of this.
So, a correlation has been shown, but causation has not. In other words, maybe because he is holding infant he is not attacked, but it also could be that when he is holding the infant, he is trying harder not to provoke an attack since he is supposed to be protecting it.