Hey ladies and lads, I’m doing the second half of Part 1 of The Primate Anthology, also known as pages 44- 87. APOLOGIES IN ADVANCE FOR LENGTH, I KNOW IT IS VERY LONG.
Chapter 6: Daughters or Sons
In many cultures, boys are more “beneficial” than girls. They are stronger, carry the family name, and they do not require large dowries in order to wed, like some daughters. So why, after all these years of attempted selective birthing (selective abortions, infanticide, etc), haven’t we as a species developed into one that can produce the desired sex at will? Other species in the world have already accomplished this feat. The Atlantic silverside from North America that are born in relatively cool water are mostly females, while those who are born later when the water has warmed up are mostly males. Fig wasps also produce an interesting case. Their fertilized eggs become daughters, and unfertilized eggs become sons. In this species, the mother can choose which sex the offspring will be; she stashes away sperm during mating and fertilizes the eggs at will as she lays them.
So, why? Apparently, in at least the fish case, it has a lot to do with adaptation. Fish born earlier are going to grow more than fish born later, and at least for the Atlantic silverside, being big is a advantage to females. The bigger the Atlantic silverside, the more fertile she tends to be. The fig wasp deposits her eggs in, surprise, a fig. (Surprise – when you eat one of these figs, you eat a wasp! But they are still delicious, so don’t let this deter you.) The little babies that hatch in there mate, and then leave, but sometimes the little males never get out. So for the wasp species, why would you produce the same amount of females as males? In this particular scenario, you only need as many males as it would take to reproduce with the females, roughly one male for every ten females.
What about humans? Why haven’t we evolved in a such a manner? One mathematician, Ronald Fisher has come up with his theorem of the sex ratio which basically says as long as:
1. to make sons and daughters requires equal amounts of parental resources
2. brothers don’t usually breed with sisters and
3. all individuals are given equal breeding chance
then there should roughly be the same amount of sons to daughters.
Suppose a population decides to specialize in boys, and has three times as many boys than girls. When those boys go to reproduce, only a third of them are able to do it. Eventually, this specialization in boys will no longer be favored, and girls will become the specialization until you have an unequal portion of girls. Back and forth it goes until you come out with roughly an equal ratio.
Fisher’s model only works if all his requirements hold true. For example, the wood lemmings commonly inbreed, and as a result have developed the curious ability to have a super-x chromosome. Basically, even if a lemming had a X and a Y chromosome, if the X is a super-x, the super-x will overwhelm the Y, and that individual will develop into a female.
Two gentlemen, Robert Trivers and Dan Willard are of a different school of thought. They believe parents are able to adjust the energy and resources poured into the production of offspring to produce the sex most likely to translate into reproductive success. Suppose a mother who is highly ranked has better access to food and will produce a big strapping young lad, who will go on to sire many babes, because he is so much more attractive and strong than all the other lads. Low-ranking mothers, conversely, would produce scrawny little boys who would get little to no reproductive time. It is therefore in their best interest to make girls, because they will give them more grandchildren and ensure more reproductive success than would their unattractive sons. This theory does hold up under certain circumstances. Female spider monkeys tend to produce daughters if they are low-ranking, while middle and higher-ranking produced equally boys and girls.
My question to you: Do you think that humans would benefit from having children according to socioeconomic status, or would this be harmful to our species?
Chp. 7: Ms. Monkey
This is the story of Becky, a low-ranking macaque destined for greatness. Or at least mediocre-ness. Third from the bottom, this female was often the victim of unprovoked attacks or moving out of everyone’s way. But, it would seem, she had had enough. She began her scheme to get out of the gutter and into the stars. It’s easy to see why she’d want to, higher ups get the best food and the preferential treatment from the males. They have higher birthrates, their young survive more often, and their other high-ranking friends defend each other. So, she began courting the high ranking females she had previously shied away from, grooming them and holding their babies. She started stepping into fights for the high ranking females, showing her solidarity, and they reciprocated when she herself got into a fight.
What’s interesting about this is that no other females had significant change in rank, except for our dear Becky. Primatologists had assumed that moves up the social ladder only happened when unusual events occurred leaving an open space, but Becky showed that higher rank can be achieved by ingratiating behavior. She made important friends, and they helped her out. Primates have the ability to track complex relationships and remember individuals, which may indicate a conscious level of decision making. The development of said social skills may have even played a large role in the evolution of the primate brain. Could Becky have intended for this rise to happen? Was she cunning and made such calculating moves? It’s hard to say. However, even in the primate world, friends in high places obviously can’t hurt.
Chp. 8: In the Minds of Monkeys
Monkeys and apes are capable of predicting the behavior of other animals, and to recognize their own relatives and allies. Like the case of Becky above, this has led some scientists to speculate that perhaps primate intelligence evolved to solve social problems.
What kind of social knowledge do monkeys have? Vervet offspring assume their mother’s social rank. While males migrate out, the females have only a few choices in making their social standing improve. To do this, they establish close bonds with higher-ranking females, in addition to maintaining their tight family bonds.
Because of these bonds, hostility between two animals tends to extend to whole families. In order for this to happen, they have to know who is allied with whom, and who will aid their adversaries. Fights between one vervet and another from another family could escalate into their relatives fighting each other later.
Vervets and other primates, interestingly, attempt to hide and falsify signals and behaviors. Vervets have specific “alarm noises” for different sorts of predators. Some have been seen to consciously sound a false alarm to their own ends, for example, to scare away new male migrants.
An example of a Vervet Alarm (<–click me!)
Other primates attempt to hide their social cues or behaviors as well. Chimps have been known to try and hide signs of submission, and baboons have been shown to try and hide their signs of anxiety. Humans are able to take skills and knowledge from one area and extend it to another – which leads me to my question:
Do you think other primates are intentionally misusing social cues to their own ends? Further, what do you think about the postulation that primate brains evolved to solve social problems?
Chp. 9: The Bonobos’ Peaceable Kingdom
Bonobos have a reputation in the world as being the peace-seeking, sex-loving primate. However, bonobos are hostile like any other primate; they just deal with it differently. When bonobos get excited, agitated, or aggressive, instead of major fighting, they substitute in sexual behavior. While only consensual copulations were seen between males and females, the homosexual behaviors were not always so. Often these instances were seen following hostile acts (threats, chase, attacks, etc), which leads primatologists to believe that the homosexual activity among bonobos promotes reconcile and appeasement. Sexual activity is advantageous for females as well. Even sterile females mate as often as those who are able to reproduce. For females, their sexual receptivity allows them to gain acceptance to a new group with minimal hostility. Nonreproductive copulations diminish hostility and establish/maintain intimacy between males and females; males are tolerant of females and rarely threaten or attack over food. It seems that this is because in such a noncompetitive situation, individuals are no longer concerned with rank. Because of their tendency to deal with aggression in such a manner, bonobos have developed a relatively placid society.
Chp. 10: Dim Forest, Bright Chimps
Chimp on a Monkey Hunt! (video)
Tai chimps show great complexity in hunting and tool use. They often use branches and stones to crack open different hard shelled nuts, and what’s more interesting, in doing this they often show mental abilities in spatial recognition comparable to some human nine-year-olds. These chimps remember where a stone of the appropriate size for the job is, even if it is out of sight. Also impressively, chimps will use tools delicately, aggressively, or precisely according to the job at hand. Often the researchers saw a chimp raise a 20 lb. stone, strike a nut with several powerful blows, and then switch to delicate taps. Finally, they would get a small twig to pry the kernel from its shell.
Tai chimps also have impressive hunting skills. Hunting monkeys successfully requires at least three motivated individuals working as a group. (The video though, I believe shows only one, so it was interesting he was successful, considering lone chimps succeed about 15% of the time.) Accordingly, chimps more often than not hunt in groups. Tai chimps use group effort to spread out and then surround and enclose their prey, meaning that they all need to coordinate their movements. They owe a lot of success to their organization.
Do you think this type of hunting strategy could be a type of social behavior scientists would attribute to the evolving of the primate brain?
Chp. 11: Leading Ladies
In baboon society, often elderly females serve as leaders at critical times in group movements. Why would this fall to an elderly female and not to, say, a young strong male? Or a high ranking male? It may because the only permanent members of baboon societies are the females; males migrate out. Often the most prominent and influential female also is the one who hast he most descendants in the group. For baboons, motherhood happens throughout their lives, and is a way to renew and reinforce social ties. These ties are furthered by grooming, which is more actively engaged in by the female relations in a group. Sons stop reciprocating their mothers’ grooming and have interactions with others outside their mother’s family. When they eventually migrate out, they have to compete for social rank, which they do not keep as they get older. For these reasons, males in a group do not have the social ties and resources that females do, leading to the elderly females to be the decision makers in the group.
Chp. 12: To Catch a Colobus
The Gombe Chimps!
In a method that seems counterproductive, the red colobus do not flee when they see or hear Gombe chimps approaching – they wait and see, instead. If chimps attack, they counterattack in response to the predators. More often than not, the outcome is in favor of the chimps, and the best the red colobus can do is minimize their damage to a single group member. Why don’t they scatter? Well, that’s worse. The chimps nearly always catch one or more of them. They stand a slightly better fighting chance if they just wait it out.
But sometimes, chimps don’t hunt the colobus, even though conditions seem exactly the same. One theory is that chimps attempt to trade sex for meat. Chimps will hunt the colobus when there is at least one estrus female in the hunting party. The male hunters then preferentially give the sexually receptive female the meat.
Chimps don’t always give meat to just estrus females. They also use it in a political and social sense, but giving it to their allies and not to their rivals. This type of “selfish” goal may be what prevents Gombe chimps from being as cooperative during hunting as the Tai chimps from the above article.