14 Primate Behavior

In this lecture, we are going to talk more in depth about some of the behaviors that were introduced in the primate taxonomy lecture.

Primate behavior is very complex and is influenced by a number of factors, including our genes,

environmental factors, such as culture and learning, and hormones and chemicals. If we look at the emotional disorder of depression, depression is often described as a chemical imbalance, and often those chemicals are attributed to serotonin and dopamine.

In more recent years, research has shown that our emotional and mental states can also be influenced by our gut bacteria.

And individuals that have healthy gut flora are less likely to become anxious or depressed. The point is, is that behavior is very complex, and it can be influenced by factors we have yet to discover.

When we are looking at behavior, we are looking at interactions between genetic and environmental factors.

Because environmental factors are at play, behaviors are not fixed and can be modified by experience.

Behavioral ecology is a branch of primatology that looks at primate behavior. In particular,

behavioral ecologists look at the interconnections between biological components of ecological systems as they evolve together.

And so to understand primate behavior, we can't just look at biology or individual primates in isolation.

We have to look at the interconnectivity of that individual primate with their environment, whether that is social environment or, or

physical environment, including other animals, plants, and microorganisms.

And we have to look at how all of these different components evolve together. An example of a behavioral ecology approach to understanding primate evolution would be the flowering plants hypothesis that we talked about in an earlier lecture.

So behavioral ecologists focus on the relationships between the individual and social behaviors, natural environments, and also various physiological traits.

Natural selection then acts on those behaviors. And we're talking about environments. We're talking about how behavior is influenced by both current and past environments.

So these behaviors are selected for and inherited by offspring from parents.

Certain behaviors give individuals a reproductive advantage, right? These are advantages that help the individual survive and reproduce.

Those behaviors then are acted on by natural selection and passed down to subsequent generations. And so those behaviors could include mating behaviors, parenting behaviors, and also toolmaking.

Primate behaviors that we're going to focus on in this lecture are

social organization,

sex and reproduction, communication and culture.

First, we'll begin with social organization. There are five different primate social structures.

Solitary monogamy, polyandry, polygyny, and bachelor groups. We will go over these one by one. The first social structure that we will talk about is solitary.

This refers to adults spending most of their time alone, and they occupy separate individual territories.

And so examples of solitary primates are orangutans and lorises

Oftentimes, male and female orangutans are solitary. If a female has an offspring, then it's just the female and their offspring.

During mating season, that is when males and females will meet and see each other. But otherwise, throughout other times of the year, they occupy separate territories that do not overlap.

Monogamy refers to social structures that are one adult male and one adult female and their offspring.

These are species that pair, bond for life and they work together to raise offspring. So examples of monogamous species are marmosets, gibbons and siamangs.

Polyandry refers to one adult female and multiple adult males and their offspring. This social structure is common in primates who give birth to twins.

And so an example of a polyandrous species are tamarins. There are two different types of polygynous societies.

Single male polygony refers to one male, multiple females. Multiple male polygeny refers to multiple males with multiple female partners.

And so examples of polygynous societies are chimpanzees, macaques, lemurs and squirrel monkeys. Bachelor groups refers to all male groups that do not yet control a territory or, or a group of females.

Typically, these are males that live in polygynous societies where there is competition for mates.

However, these are males that are either too young or too weak to become alpha males and so do not have a group of their own.

And so they get together and form their own bachelor groups. And so examples of species that form bachelor groups would be chimpanzees and gorillas.

Factors that will influence what type of social structure a primate lives in are body size and diet. And so these are factors that will influence if primates live in larger groups or if they will live in smaller groups.

In regards to body size, predation is a factor.

Smaller bodied primates tend to live in larger groups because they are much more vulnerable to predators.

Living in a large group has two advantages. One is there's strength in numbers when it comes to defending yourself and your territory.

And two, allowing more members in your social group has the advantage of having more lookouts. Second is diet.

And two factors that influence diet are your basal metabolic rate and and distribution of resources. Basal metabolic rate, or BMR refers to the rate in which your body burns calories or uses energy to maintain bodily functions at a resting state.

In other words, it is the amount of calories you have to burn to maintain homeostasis. Smaller animals have a higher BMR and and so therefore they must eat energy rich foods that are higher in protein, fats and carbohydrates.

Such as insects.

Larger animals tend to have a lower bmr, meaning that they can get away with eating less energy rich foods, such as leaves or grasses.

Energy rich foods require more effort to obtain. Oftentimes, these are insects or animals that you have to hunt.

Less energy rich foods require less energy to obtain. However, they require more energy to digest. And so those species tend to have elongated intestines.

They have intestinal bacteria and enzymes. Primates that eat insects then tend to live in solitary social structures or much smaller social groups, because they feed alone or in pairs.

The reason why primates who tend to eat insects or higher energy foods live in solitary or smaller social structures is because there is more competition for food.

Also, if you're hunting an insect, you cannot hunt an insect in a large group. That insect will hear you coming, coming from a mile away.

And so, in order to ensure hunting success, those primates tend to hunt alone or in pairs.

Primates that eat fruits, nuts and berries, which are seasonally available, tend to live in larger groups and are territorial.

Fruits, nuts and berries are not plentiful throughout the forest. They are only plentiful in small batches.

And so in order to successfully exploit these small batches, those groups have to defend those territories.

And so the social structure that is most common in primates that eat these seasonally available foods are either male or female dominated groups, groups that have a strong social structure or social hierarchy and have alpha males or alpha females.

Primates that eat leaves, which are abundantly distributed, tend to live in social structures that have one male unit.

So an example of that would be a gorilla. In gorilla societies, you typically have one alpha male

and females and their offspring. All of those females

mate with the alpha male, and all of the offspring of those females are the offspring of the alpha male.

In these social structures, there is very little competition for food because these food sources are abundantly available.

Next, we'll talk about sex and reproduction.

Estrus, which was mentioned in our previous lecture on primate taxonomy, refers to physiological and behavioral changes that indicate a female's readiness to mate.

And so examples of physiological changes that happen might be that swelling and redness of the genitalia.

Behavioral changes could include making smelly marks. Female lemurs, to indicate their readiness to mate, will pee on trees.

Consortships refer to temporary male female relationships while the female is in heat. Consortships within the primate order are much more common than pair bonding.

Other strategies that we'll look at are dispersal, sexual selection and parenting. Dispersal refers to members of one sex leaving their natal group when they become sexually mature.

Dispersal is advantageous because it reduces competition between males for mates and it decreases the likelihood of close inbreeding.

Male dispersal is the most common pattern and is practiced by ring tailed lemurs, vervets and macaques.

Female dispersal is less common but is practiced by colobus monkeys, hamadryas, baboons, chimpanzees and gorillas.

There are two different reproductive strategies. K selected refers to species that produce very few young and have long parental investment.

Primates are an example of a K selected species.

The average

period between

offspring is eight years. Primates will usually wait eight years between their offspring. We also know that primates give birth to one offspring at a time.

K selected species also tend to be longer lived.

They live in predictable environments that have very little change. And because they have longer lifespans, they often reach sexual maturity much later in life.

And they have longer birth intervals, typically about three to five years. Primates have an even longer interbirth interval at eight years.

R selected species refer to species that produce many young with very short parental investment. And so examples of our selected species would be fish and insects.

If you remember the mayflies that we talked about in a much earlier lecture. They are born, they live for 24 hours, they reproduce and they die.

And so these are species that have very short lifespans. They live in unpredictable, ever changing environments.

Because their lifespan is so short, they reach sexual maturity at a much earlier age. And they have very short birth intervals, so there's very little time between offspring.

Infanticide is a practice that is common in polygynous societies. And so infanticide occurs when there is a new alpha male.

The new infanticidal alpha males do not kill their own offspring, but kill the offspring of the former alpha male or of other males.

Once a male has killed an infant, he will subsequently father a new child with the victim's mother.

The reason for that is if you're an alpha male, you don't want to spend precious time and resources rearing offspring that are not your own.

Another reason for infanticide is that breastfeeding is a form of birth control. And so the sooner you kill the offspring of a breastfeeding female, the sooner that female will become sexually receptive and you can father a new child with that female.

I will link this clip below. It is a clip of macaques in India, and it shows the arrival of a new alpha male and the infanticide that occurs after his arrival.

Sexual selection refers to traits in males that lead to greater success in acquiring mates.

Sexual dimorphism Is a catch all term that refers to the physical differences between males and females that allow males to attract females.

Sexual dichromatism refers to the different coloring in males that make them more attractive to females.

And so a great example of sexual dichromatism are these mandrills. Male mandrills have these very colorful faces.

Female mandrills in comparison, look very boring and drab. And so sexual dichromatism is one form of sexual dimorphism.

Other forms of sexual dimorphism include size and other physical features, such as face phalanges in orangutans, Blue canine size in baboons.

In terms of parenting, primates are primarily polygynous.

There are a few primates that are monogamous, but that is definitely not the general trend. Because primates are polygynous, males are invested in reproducing with as many females as possible.

And so males are typically not involved in the rearing of their offspring. The much more common pattern is the mother infant bond, with the exception in monogamous or polyandrous species.

So for the most part, it is typically the females that are responsible for child rearing.

This behavior is learned. It is not instinctual.

We know this because orphaned female apes raised in captivity do not know how to care for their infant if they don't have a model of their own.

And so oftentimes these, these females who have spent their entire lives in captivity, when they have offspring of their own, they have to be monitored very carefully because they can injure or kill that offspring.

There are two different types of communication. You have autonomic responses and intentional behaviors within intentional behaviors.

We are going to talk about aggression, dominance and submission, and altruism.

Autonomic responses refers to responses to threatening or novel stimuli. Novel meaning new. And so autonomic responses might include raised body hair, body posture, and enhanced body odor.

Autonomic responses refers to responses that we have no control over. You can think of them as instinctual behavior.

And so good examples of autonomic responses that, that we have are goosebumps, right? When it is cold or when it is scared.

So when it is cold or when we get scared, our skin will break out into goosebumps. We don't really have any control over it.

Another example would be increased heart rate, right? So when we are scared, when we are nervous, when we are excited, our heart rate will increase.

We have no control over it. We can't tell our heart, hey, heart, be slower, right? So these are autonomic responses,

Intentional behaviors In contrast, we do have a certain amount of control over.

And so some examples of intentional behaviors are gestures, facial expressions and vocalizations. Primates also communicate using facial expressions, gestures and vocalizations.

However, their facial expressions might not map onto our facial expressions. And so for us, a smile is a sign of play.

It's a sign of friendliness. For chimpanzees, that is quite different. A relaxed face is, when the two lips are closed, what we think of as a smile.

Chimpanzees will interpret it as a fear grin. So fear and excitement, distress, even a sign of aggression.

Primates also have very sophisticated vocalizations. Marmosets, for example, have different vocalizations for different predators.

And so they may make one vocalization for a hawk and another vocalization for a snake. In this clip that I will link below shows chimpanzees at a zoo and some of the sophisticated gestures and vocalizations that they use to communicate with one another.

And so a big question is, do chimps have language?

And the answer is yes and no, depending on who you ask. And so if you ask a primatologist, they would say yes.

Chimps have language.

Different chimp societies have vocalizations and gestures that are unique to them. And chimpanzees are constantly inventing new gestures and vocalizations.

If you ask a linguist,

they would say no. And the reason why linguists would see chimps as not having language is because in order for a language to be considered a language, you have to be able to talk about things that are imaginary or non present, and you have to be able to make propositions or plans for the future.

And so for that reason, because chimpanzees can only communicate in the present moment, and they cannot talk about events in the past or in the future, and they cannot talk about imaginary or invisible objects, linguists would say that chimpanzees do not have language as we know it.

Other forms of communication include aggression. And there are two different types of aggression. There is intragroup aggression, and so that includes aggression that is practiced within a social group.

Extra group aggression refers to aggression that is displayed between social groups. There are two different forms of intra group aggression.

There is aggression when it comes to competition for food, and there is aggression when it comes to competition for mates.

Females are often the ones who engage in aggression over competition for food, particularly when it comes to feeding their offspring.

In regards to competition for mates, it is usually aggression that is practiced by males.

Extra group aggression is aggression that is practiced between groups. And so this usually occurs in species that are territorial, and so Chimpanzees would be a great example of a species that practices extra group aggression.

Within chimp society, there is a core area. This is the area with the highest concentration of predictable resources.

Chimpanzees are one of those species that eats highly, seasonally available foods like fruits, nuts, and berries.

And so chimp societies that live in core areas have to defend their territories from other chimp societies if they want to retain access to this core area.

And so here what you're seeing is a group of core chimps in a society forming a security patrol. Dominance, or dominance hierarchies, refers to imposed orders by establishing parameters for individual behaviors.

Who has access to mates, who has access to food, who has access to resources. And actually, dominant behaviors reduce the amount of actual physical violence.

The reason for that is oftentimes the threat of violence by an alpha male or female is enough to keep the subordinate

individuals in check. Dominance then refers to behaviors that control access to food, resources and mating partners.

And oftentimes, alpha males and females have higher rates of infant survival and their offspring produces more offspring.

The reason for that is that the offspring of alpha males and females often have

a richer diet. And because they have a richer diet, they reach sexual maturity faster and reproduce more.

And so alpha males and females not only have more offspring, but their offspring produce more offspring compared to subordinate individuals.

An alpha male and female's position in a hierarchy is not permanent, but constantly in flux. And so some factors that will determine

whether or not an individual is an alpha male or female is their gender, sex,

age, level of aggression, time spent in group, intelligence, motivation. And sometimes that position is inherited.

So the mother's social position,

submission, refers to touching, patting, hugging, holding hands, and grooming. These are behaviors that signal to other individuals, hey, we are friends, right?

We are on the same side. So here's an example of two baboons hugging.

In this clip that I'll link below are snow monkeys or Japanese macaques. And you'll see that one way to reinforce group bonds is by grooming.

Affiliative behaviors include behaviors that cement social bonds within the group. And so that can include reconciliation or apologizing after a dispute, consolation, and also simple amiable interactions such as touching, hand holding, hugging, and kissing.

So, affiliation refers to behaviors that strengthen the bond of a group. Altruism, in contrast, refers to acts that benefit others at the risk or sacrifice of the performer.

And oftentimes, altruism is a good indicator of empathy. And so examples of altruistic behaviors are comforting an ill or dying relative or Friend.

What you'll see is

chimpanzees, for example, will bring food to a member who is ill or dying. That is an altruistic behavior because that chimpanzee could be eating that food for themselves, but instead they are sacrificing that food for their relative or friend.

Other examples of altruistic behavior are protecting victims during an attack, putting yourself in bodily harm,

and adopting orphaned young.

It's usually an older sibling, but sometimes it could be a bachelor that will adopt an orphaned young.

In this clip that I'll link below is an example of an affiliative behavior. It is two bonobos kissing.

I have to warn you, it is pretty graphic and definitely PG13. Last, we'll talk about non human primate culture.

The reason why we're calling it non human primate culture is because we, we are primates too. And so our culture is human primate culture.

And so non human primate culture refers to all the other species besides us that have culture. Cultural behavior is learned.

That means that it is knowledge that is passed down from parent to offspring or from peer to peer in a social group.

These are behaviors that you are not born knowing how to do. And, and so cultural behavior is in contrast to instinctual behavior.

Instinctual behavior are behaviors that you're born knowing how to do. And so some examples of cultural behaviors would be food items, so what is good to eat and what is not good to eat.

And also other behaviors such as tool making. And so here we have an example of a capuchin monkey, and he is carrying a stone.

He's going to use that stone as an anvil to break open nuts. Another example of tool use. This is a female gorilla.

You can see that she's crossing this river using a walking stick. She's using that walking stick first to test the depth of the river, and then she's using that walking stick to give her stability as she is crossing the river.

In this clip that I will link below, these are Japanese macaques that live on the beach, and they have a behavior that is particular to this troop.

No other Japanese macaque societies practice this behavior. And that behavior is washing sweet potatoes in the ocean.

And so the way that they get rid of the sand from the sweet potatoes is that they wash it in the ocean.

And the water benefits from, of course, taking the sand out. But also the macaques like the salty taste of the ocean water on their sweet potatoes.

And again, this behavior is unique to this one macaque society. When it comes to non human primate culture.

The best Example would be chimpanzees. Chimpanzees have one of the most rich non human primate cultures.

And a great example of their rich culture would be tool making. Chimpanzees are the great toolmakers.

And so some of the tools that they use are leafy sponges. They will use leaf sponges to dunk into pools of water, and they will wring out that sponge into their mouth.

And so they use these sponges to drink water. They also use these sponges to clean themselves. They also practice termite fishing.

And so they'll find a branch that is

not too thick, not too thin, but is flexible enough. They'll strip all of the leaves off this branch, and they will dunk it into a termite colony and pull it out and eat the termites from this branch.

They also use branches, and they'll sharpen the edges of the branches, and they will use these spears to hunt smaller primates like galagos or bush babies.

Chimpanzees also use rocks as anvil and hammer stones to break open nuts. So those are just some of the examples of tools that chimpanzees use.

When we look at chimpanzee tool making, it tells us a lot about their intelligence. Chimpanzees plan and they have forethought.

We know this because we see chimpanzees keep rocks, rocks that are particularly great at acting as anvil or hammerstones.

Rocks that they don't need at that exact present moment they will keep for future use. And so that shows planning and forethought.

You also see regional variation. Meaning. Meaning that not every chimp society will use the same tools for the same job.

For example, one chimp society might use leafy sponges to collect honey. Another chimp society might use twigs to perform the same task.

Another example of regional variation is diet preferences. And so, again, diet is a cultural behavior.

It is something that we learn. We learn what is good to eat from our parents. And so a good example of regional variation when it comes to diet is the oil palm fruit.

Some chimp societies will eat oil palm fruit, and other chimp societies will not eat oil palm fruit, even though it is readily available in their territory.

And that's because those chimp societies were never taught or never learned that oil palm fruit is edible and good to eat.

And this clip that I will link below talks about the differences between human culture and non human primate culture.

And we'll see that the biggest difference is cultural transmission, that in human societies, we are able to pass down our knowledge across distances and across history.

Because we have symbols, we have written systems and artwork. Primates, because they don't have control of symbols, they don't have a writing system or artwork, they do not have cultural transmission.

And so if we go back to the macaque example, those beach macaques in Japan that have learned how to wash their sweet potato in the ocean, if that troop of macaques happen to be struck with a virus and that entire society is wiped out, that knowledge is wiped out with them.

In our society, if there was

a mass extinction event and there were only a couple of human survivors, they would be able to access knowledge from the past, because we have that knowledge encoded in books and in artwork and in other media, and so that knowledge would not be lost forever because of these symbols and writing systems.