Social Relationships between Males and Females

Demographic Constraints on Male-Female Relations

Let's look at the different types of social system which can affect male-female relations:

Monogamous system, like in gibbons.
There is little opportunity to form relationship besides the one with the mate, so there's not much complexity in choosing who to mate with and who to hang out with. People have done preference experiments in the lab and it has been shown that monogamous animals even when given a choice, choose their usual partner to associate with.

Polygynous system, like in the gorilla.
The females are not related to each other and so have little to offer each other socially. The male protects the females from outside males. Long-term bond form between the dominant male and the female sin his group- if he disappears, the females all disperse.The females are submissive to the male, and take more of the responsibility for staying near the male and maintaining proximity. The subordinate males do tend to hang out with females more than other females, but these proximities are the responsibility of the subordinate males, not of the females he's hanging out with.

However, remember the differences between gelada and hamadryas baboons; They both live in one-male groups with several females, but because of dispersal differences, the relationships are different.

Gelada baboonsHamadryas baboons
Female-bonded; males disperseMale-bonded; females disperse
If the male disappears, the group will still stay together and probably find another male.If the male disappears, the group will disperse. He holds the group together by aggression and herding.
The females are power brokers and have a lot of influence in which males will join the group.There is a lot more competition and less cooperation among the females. (Since they're not related.)

Multi-male, multi-female system, like the common chimp.
The females are mostly solitary in the chimp, so they haven't been studied as much, since males and females don't have too much contact outside of estrous periods.
In bonobos, however, males and females spend a lot of time together. Females maintain strong relationships with their sons even after they're grown. Females are also sexually receptive throughout their lives, even when lactating or pregnant.
In Savannah baboons, male-female relationships have also been studied. They're a female bonded group, and most grooming and alliances occur within matrilines. There is extreme sexual dimorphism (2:1 ratio) and the males have much huger teeth than the females. Studied show that the higher ranking males do get most of the matings, but the lower-ranking males get more than their share as well.

Why? Female mate choice. Why would they prefer these low ranking males? We must look beyond their estrous period and into the rest of their lives; Baboons give birth every 5-8 years. After birth, they lactate for about two years, with no cycling. They only go through about 5 cycles before they conceive again, and their gestation period is about 6 months. So, they spend about 10% of their lives cycling, and that was usually the only portion that people studied when they wanted to know about mating behavior. Barb Smuts looked at the other 90% of their lives and how that affected the mating behavior.

Friendship in Baboons

She found that females have certain guys that they spend most of their time with. A female spends very little time with most of the males but much time with one male. This was a surprising find in a species we had always termed promiscuous. She termed these pairings "friendships," and defined friendship in terms of proximity and grooming. Females spend a lot of time in close proximity with their friend, and almost no time with other males. If grooming were randomly distributed throughout he groom, then you would expect that any pair would be grooming each other about 6% of the time, but friendship pairs mostly (or even exclusively!) groom together.

Most female shave one friend or maybe two. Besides proximity and grooming, they often travel together, feed together, and solicit grooming from each other. The female is relaxed around her friend. Usually, when a male approaches, the female goes through ritualized submission- she presents. However, when it's a friend who is approaching, the females don't do this.

So, who is maintaining the relationship? Robert Hinde can up with a system to quantify this. You watch any time a female or a male in your target pair approaches or moves away from the other. Then you subtract the percentage of the time that the female leaves from the percentage of the time that the female approaches. This gives you a continuum from -1 to 1. If your number is -1, then the male is responsible for maintaining the relationship, while if you get 1, the female is. At 0, they're both doing it. When they apply this to baboon friendships, they find that in most cases it's the responsibility of the females to maintain the friendship, but in some pairs, it's the male. If they're both doing some of the work, then what are they each getting out of it?

Benefits to Females

Benefits to Males

"Friendships in the past doubled the probability that a male would form a consortship with that female in the future."
Also, beside increasing mating probability, there's another benefit which may be important- the male often uses the baby of his friend to fend off aggression from other males; when someone threatens him, he grabs the kid because the other guy knows that if he hurt the baby he'd be mobbed by the mom and her matriline.

So, the males increase their mating chances, while females increase their survival and that of their infants- so this is a case of reciprocal altruism.