www.UsHumans.net: Chapter 7
Behavior of mammals
This chapter contains a brief discussion of the behaviors that are common to all mammals, including us humans, so that we can begin to form a more accurate picture of the behavioral differences between ourselves and the other mammals. This chapter is a summary of Social Behavior in Mammals by Trevor B. Poole. You might like to read his entire book to get a more thorough description of the behavior of mammals. Primates are the mammal sub-category consisting of monkeys and apes; humans are one type of ape. The anatomical features that distinguish primates from other mammals–and humans from other primates–were discussed in the last chapter. The next chapter contains a description of the behavior that distinguishes primates from other mammals and the behaviors that distinguish humans from other primates. This will help us more accurately distinguish what it is to be human.
Numerous websites include pictures and videos of animals and their behavior. You might like to search PBS videos at www.pbs.org/wnet/nature/database.html and www.pbs.org/wgbh/nova for one-minute clips of various animals and behaviors. The ARKive Images of Life on Earth website has photos and video clips of numerous animals at www.arkive.org. For animal webcams, visit www.nationalgeographic.com/channel/crittercam, www.birds.cornell.edu/birdhouse2/nestboxcam, http://nationalzoo.si.edu/Animals/WebCams, or www.africam.com. Visit www.pbs.org/wnet/nature/animalmind for studies of animal intelligence. For a list of other websites, see http://nature.ac.uk/text/browse/591.5.html.
In the previous chapters we saw that mammals evolved from reptiles and that certain physical characteristics distinguish mammals from those reptiles. For example, mammals have hair that helps regulate body temperature (there are no hairy lizards). Even humans and elephants have hair; it is just finer and more sparse. When you are cold, you sometimes get “goose bumps” that futilely try to raise your now-less-thick-hair for added heat retention.
There are also very important behavioral differences between mammals and reptiles. The most crucial of which is that reptiles are not parents. They lay eggs and then leave the eventual offspring to fend for themselves. Besides mammals and birds, few animals have parenting behaviors. Some exceptions include rattlesnakes, centipedes, seahorses, and some species of fish–for example, the Cichlid fishes (visit the Cichlid website at http://malawicichlids.com/index.htm.) Mammals are parents. Mammalian young develop within their mother's body and are born live. The mother feeds her young using her mammary glands for the next few weeks, months, or years, depending on the species. The close relationship between mammalian mother and child doesn’t exist in other animals. In each monogamous species, there is a similarly close relationship between father and his offspring. Mammals protect their young, teach them how to live, and raise them to maturity. Parenthood forms a large part of what it is that makes us human. You might like to visit Baby Tales at www.pbs.org/wnet/nature/baby.
For most mammals, it is the female who takes care of the offspring. For photos and descriptions of a few exceptions, visit www.pbs.org/wgbh/nova/seahorse/superdads.html.Parental care consists of cleaning and grooming, transporting, retrieving, bringing food, defending, babysitting, and teaching. Offspring are taught by example. They watch their mother to learn everything that is necessary in life, including which foods to eat, how to make nests, and the details of inter-species behaviors and such. (Is this culture? Human culture consists of our recipes for how to do everything occurring in daily life. Parents teach culture to their offspring. It consists of everything learned–all that is not innate.) We humans learn most effortlessly simply by watching and then doing. This practice is older than language.
In Chapter 5, we saw that the time-sequence of changes in the individuals of a species is described as evolution and that it occurs through natural selection by the environment of climate, predators, and food. This is Darwin's principle of evolution by natural selection. This principle points out the natural situation that the traits of the individuals who live long enough to have children are passed on to those children. Behavioral and emotional traits are also passed on to successive generations and are subject to the same rules of natural selection. Of particular importance to us humans, parenting behavior developed concurrently with parenting emotions, and social systems developed concurrently with social emotions. Love, sympathy, and empathy are our parenting emotions. Our social emotions consist of sympathy, empathy, pride, embarrassment, guilt, and shame. Our social system and the Golden Rule necessarily developed simultaneously because neither occurs without the other. Such behaviors and emotions developed because those individuals having them proved more likely to live long enough to produce offspring who in turn inherited these characteristics. Altruism is another example of social behavior. It is often observed that an individual vocally warns its group members that a predator is near even though the act of giving this warning means running the risk of becoming the meal of that predator. An individual benefits in helping others survive if its action will be repaid in kind by others in the future.
Our feelings and emotions necessarily involve those things that are of biological importance to ourselves; we pay no attention to other things, such as the third branch up from the bottom of a bush. Individuals of a species are always very interested in others of their own species. For example, a dog goes a little berserk when it spots another dog. This is in contrast to the way it ignores thousands of other events, such as the wind-blown motion of grass, that are constantly going on around it. Much of behavior involves interactions with other members of the species, especially those within the local flock, group, or band. Mammals often live in small groups of individuals where access to feeding and mating and such is determined by a dominance hierarchy in which each member has agreed to a sort of ranking. Intergroup fighting is limited by this dominance hierarchy.
General mammalian behaviors include feeding, play, communication, relations with others of the same group and with other groups of the same species, defense against predators, dealing with the climate, reproduction, and child rearing and training. For the last fifty million years, these have been the daily activities of our direct ancestors, as they are for us humans still today. Visit www.nps.gov/deto/dogs.htm for an overview of the prairie dogs and the geology and native mythology of the area of Devil’s Tower.
Food packet size determines social size
Food-getting plays an important role in every animal's daily life. Mammalian species have three general approaches to finding food. If the food of a species is found in widely scattered places and occurs in such small quantities that only a single individual can make a meal of it, then that species often consists of lone hunters, some examples include coyotes and house cats. If instead, food sources are widely scattered but occur in group-sized bundles then the members of that species typically forage as a group and then share the food when it as found. This is the approach typically adopted by us primates. When food is so abundant that it is within each member's constant reach then it plays a smaller role in their behavioral interactions, as happens for the grazing mammals such as gazelles and horses.
If there is a moderate food supply, the members of a species may mark-out a territory reserved for their own use. Those mammals who live in areas that have either widely scattered or abundantly available food sources will not be territorial. Sometimes a male will mark out a large territory that includes the smaller territories of several females with whom he will mate.
Within any region, the total population of a species is limited by the total amount of food within that region. Biologists refer to this as the region’s carrying capacity. This applies to us humans as well. The population of gatherer-hunters is typically one person per square mile (2.5 per square km) because that is the carrying capacity of the land. Multiplying by the total land area of the Earth gives a worldwide gatherer-hunter population limit of about fifty million persons. By planting crops, we have been feeding many more persons, but what is the total number of humans that can be fed by agriculture?
Mammals are more adept at communicating than are the more primitive reptiles, fish, and worms and such. Birds communicate by song and dance. For example, photos of dancing blue footed boobies can be seen at the Darwin Foundation’s website at www.darwinfoundation.org/misc/kids/6.html and an on-line video clip is at http://farallonmedia.com/quicktime/Booby%20Dance.mov.Mammals communicate specific emotional states by touching other group members, examples include grooming, affection, or a firm bite. Mammals also communicate using odors, sounds, sights, and body postures. Each of these modes will be discussed in the following paragraphs. (Visit http://bio.research.ucsc.edu/~barrylab/classes/animal_behavior/SENSORY.HTM for descriptions of numerous signals.)
We saw that the separate components of even the most primitive cell communicate using chemical signals. This technique has been expanded to effect communication between organs and between individuals. When an individual’s nose detects specific chemical odors, that individual’s brain causes hormones to be produced in response. A specific behavior might then result from that elevated hormone level. Chemical odors are used for various reasons. They indicate membership in a group, an individual's rank within the group, or they mark the boundaries of an individual's home territory. A specific odor indicates oestrus, which is the time at which a female can conceive. For most mammal species, oestrus occurs during only a handful of days per year but reproduction-related activities often play a large role throughout the year.
Mammals produce sounds of varying pitch and loudness in order to communicate different meanings, such as to warn others about approaching predators or to give a threat to another member of the group. Wolves, who live in small groups, make sounds to bring together the group members and to warn away other groups while coyotes, who mostly live as lone hunters, howl to indicate their territory in order to keep all other coyotes away. (To listen to wolf recordings, visit www.pbs.org/wgbh/nova/wolves/howl.html.) Communicating with sound is an option when the sound will not attract predators. Birds and monkeys in the trees are noisy because they can easily flee. Rabbits make very little sound. You can listen to samples of animals sounds, from bats to vervet monkeys, at www.wildsanctuary.com.
Whales make a repetitive song having a thirty-minute duration. Researchers find that a male whale will modify his song through the years by changing or adding notes. Some researchers have concluded that whales attract mates by singing to them. You can listen to recorded whale songs by visiting the NOAA website at www.nmfs.noaa.gov/image_galery.htm or www.whales-online.org.
Some primate species sing to other group members scattered around the forest. (To listen to various primate vocalizations, visit http://pin.primate.wisc.edu/av/vocals/index.html.) This is done to keep in contact with other group members and also to attract mates. Today's humans sometimes sing while working or playing in groups, and sometimes attract mates by singing. What role did music play in the daily lives of our distant ancestors? Is our deep relationship with music today an embellishment of an innate use of singing in order to locate and attract other group members within the forest? For humans, music communicates emotion and state of mind. For example, we distinguish happy from sad music. In The Man Who Mistook His Wife for a Hat, Oliver Sachs reports that some Parkinson’s patients suddenly begin to dance while listening to a song that had been their favorite before the disease began.
Vervet monkeys use different calls to indicate the presence of different predators. For example, one particular call warns that a leopard is approaching. Since leopards approach on the ground, all the group members instantly run up the nearest tree. Other calls warn of eagles or snakes and produce the appropriate reactions. Vervet infants at first give the leopard alarm call when any animal, even a non-dangerous terrestrial mammal, is seen. When they are wrong, the other monkeys show their dissatisfaction. Later the infants learn to distinguish the leopard from other animals. (Is this culture?) It is also interesting that, when a vervet infant cries, the other monkeys look at the mother of that infant.
Body posture communicates many things, including affection, anger, and alertness. Aggressive threats, defensive, submissive, and play postures are recognized in every mammal species. You have likely seen each of these displays in cats and dogs as well as in humans. In a unique action among chimpanzees and humans, when one individual looks or points in a direction, others will also look in that direction. You may have unsuccessfully tried to point out things to you pet.
Courtship displays can include both sight and touch. These displays must be long enough to display fitness but short enough to be completed before predators arrive. Birds are able to have long and complicated courtship displays because they can more easily flee. Birds tend to develop bright colors to attract mates, but mammals have a tendency to develop colors that provide camouflage from predators.
Many species of mammals form social groups consisting of many individuals. There are benefits to being a member of a group. For example, all members can watch for predators and alert the others to their presence. This is a mutually beneficial exchange of assistance. At the same time, the group members must compete over any limited resource, from food to mates.
Fighting is often limited by forming a dominance hierarchy. This means that within the group, each pair of individuals will come to a mutual agreement about which will have access priority over the other. This agreement is reached during their initial encounters and determines which individual will back down during future encounters. From then on, when that pair of individuals approaches an item of mutual interest, such as a parcel of food, the higher-ranking individual takes the item and the other moves on. If each encounter instead resulted in a fight and the death of one of the group members then pretty soon there would be no members left and the species would disappear from the Earth. When the members of a species do not fight to the death then those members are more likely to live long enough to have children. In the next chapter we will see that the hierarchical system of social primates consists of interacting extended families rather than just interacting individuals and that this difference gives us an important clue about our own nature.
Behaviors associated with mating
Mating plays a large role in mammalian behavior (for an on-line video about mating, visit http://farallonmedia.com/quicktime/why_sex.mov) even though a female is ready for conception–that is, she is in oestrus–only two to seven days per year. Her oestrus condition is made obvious by chemical odors, body postures, and by greatly swollen genitals. Chimpanzee genitals swell by four inches (ten centimeters). Oestrus is not as obvious in humans because a four-inch swelling does not occur. Recall also that human female mammary glands are permanently enlarged instead of being enlarged only during infant feeding. At some point in our past, there was a reason for us to have become different in this way.
Males and females have different roles and time-investments in the mating and child-rearing processes because one male is able to fertilize many females who then spend weeks or months rearing the resulting offspring. For example, there are one hundred females in an elephant seal harem. (For a photo of a seal harem, visit http://nmml.afsc.noaa.gov/AlaskaEcosystems/nfshome/nfsGallery/images/snp92harem.jpg.) Except for a few polyandrous groups of humans and monkeys (see http://anthro.palomar.edu/behavior/behave_2.htm for the case of marmoset and tamarin monkeys), there are no known cases of one female mating with a set group of several males. The male may invest only minutes during reproduction and raising, but to obtain the opportunity for reproduction he might expend time and effort throughout the year in competition with other males.
The female picks the male with the most emphasized feature. This feature might be body size, color, movement, sound, nest, or home area. The largest body size may indicate fitness, or, an individual's health may be indicated by bright colors. The length and intensity of bird songs indicate the level of health of the singer. Sometimes the fittest male is simply the one who can keep other males away from a preferred child-rearing location–and in doing so, attract female mates. Territorial species have little ritual during mate selection because the competitors are widely scattered. Males within societies of grazers grow horns and such to attract mates and have ritual battles. Researchers can find no other use for the extreme length of a peacock's tail except that it attracts peahens, see www.lhup.edu/~dsimanek/pseudo/fibonacc.htm.
Five percent of mammal species form monogamous parenting relations, so we humans are members of a small group. Monogamous fathers help in raising offspring because they know that the children are their own. Monogamous partners have a pair bond that keeps them together for a period of time much longer than that needed for child rearing. The pair show little interest in other potential mates. Affection between two mammals is shown by spending a lot of time in close contact, often grooming, body rubbing, and nuzzling each other.
Most commonly, mammals live in small groups where access to food and mates is determined by their dominance hierarchy. The most-dominant ("alpha") male of a group is the harem holder and is the only one who mates with the females; he keeps all other males away from the females. Sometimes he has the aid of a few lessor males who help him for a year or two, until one of them chases him away. The physical competition among males results in them being as much as twice the size of females. In the monogamous humans, males are only 25% larger than females.
The genetic variability of a harem-forming group is dangerously restricted if inbreeding occurs, so most species that live in such groups also have a mechanism to avoid this situation. It is often the case that females permanently remain in the group but males migrate to other groups upon reaching sexual maturity; for fewer species, it is the females who leave. For many species, the dominant male will be disposed before the entire group consists of his own offspring; he might instead drive his daughters out of the group or allow his daughters to be taken away by outsiders. Wolves do not do this; they are inbred. (For a computer model of wolf behavior, visit http://characters.media.mit.edu/projects/alphawolf.html.)
Scientists have found that at the moment the most dominant position shifts to a new male, the new alpha male might kill the group's infants. The male does this because those infants are not his and their mothers will be back in oestrus soon if they lose their infants, enabling him to impregnate them with his own offspring. This genetically controlled behavior has developed because it results in more of his own offspring. This infanticide has been observed in lions, lemurs, mice, prairie dogs, chimpanzees, and gorillas. Mothers often take their new offspring a safe distance away from the group in case of a new alpha takes over before they have sufficiently grown. Some female mice employ the counter strategy that biologists call the Bruce effect. If a female lab mouse is already pregnant when another potential father appears, she might abort her current pregnancy to become pregnant from the new father without him committing infanticide and wasting her full reproductive efforts. If mating is not restricted to just the single most dominant male then infanticide will not occur. In these so-called promiscuous species, such as Bonobo chimpanzees, infanticide is not practiced because each male is as likely as all others of being the father of any particular child. In monogamous species, such as us humans, fathers know the infants are their own and so do not practice infanticide.
In this chapter we have seen that the basic behaviors of any mammal species consist of similar activities. Since we humans are also a mammal species, these behaviors form a large part of what it is that makes us human. The most important way in which mammals differ from amphibians, reptiles, and insects is that adults take care of their young; this is summarized by the term "parenting mammal." Parenting mammals nurture their young. We humans are parents who care for our children. Many of us wold say that we live for our children and that very little is as important to us as are our children. (Would a mouse say the same thing?) Our nuclear family and our monogamous parenting strategy form a large part of what it is to be human.
To better understand the natural behavior of humans, we have had a look at the general behaviors of all mammals. Think carefully about the meaning of the statements that we are animals and that we are mammals. You might like to list your daily behaviors and decide which of these are common to most every animal or to most every mammal. You might also try to figure out which of your general behaviors are missing from the above list of typical mammalian behaviors: do they involve your extended family or your culture?
It is also important to point out that animal behaviors are also subject to natural selection (evolution). For example, the parenting behaviors and parenting emotions of mammals necessarily developed simultaneously. In the next chapter we will see how primate behavior, including that of us humans, is much the same as that of the other mammals except that primates have more complicated social systems consisting of interacting extended families rather than just interacting individuals. We swill see that social behaviors and social emotions in primates necessarily developed simultaneously. These similarities and differences give us important clues about our own nature.
Questions
1. What does it mean that we are animals? List your daily behaviors and indicate which of them are common either to mammals, all animals, or only to humans. Which of your general behaviors are missing from the above list of mammalian behaviors? Do they involve your extended family or your culture? Compare your list with those from other persons. Which items were included on the lists of most everyone?
2. Compare your daily behaviors with that of a reptile or your pet.
3. Compare the ways we humans cooperate with the ways other animals cooperate.
4. Compare your parenting behaviors with those of another mammal. How about other types of animals like birds, insects, or fish..
5. Compare your human mate selection criteria with those of another mammal.
6. Compare your communication techniques involving odors, sights, and sounds with those of another animal.
7. List some human body postures that mean the same thing to all the members of a single culture. Can you find some that mean the same thing to every person on the planet?
8. Describe funny, suspenseful, happy, and sad music. Does every human agree with your description or just those who are members of your culture? Are you attracted to musicians? When you hear a song from your past, how does it transport your mind and emotions to that past time?
9. When and why did we begin forming monogamous parenting relationships that last for a lifetime? Is this behavior genetic or learned? What would have to change in our biology before this system could change? What is the "divorce rate" of other monogamous species? How does the divorce rate vary among human cultures? Is every human culture strictly monogamous? What role did language play in choosing our lifelong mates? How many words and gestures were we making one million years ago?
10. How would our society and civilization be different if we formed harems? What if we produced batches of one hundred children that we then left to grow on their own?
11. Do we have a dominance hierarchy? Why do you form friendships with others? Do you ever form friendships to plot the overthrow of the leader of your group? Do you have a group leader? If so, why is that person the leader? Under what circumstances do you have a leader?
12. Do gazelles recognize their siblings and the other members of their extended family? Will two gazelles that are brothers generally compete for the same female within the herd? Do human brothers do this?
13. Is our rectangular cross section related to our universal idea of dividing directions into the four box-parts: north, south, east, and west? If this is true then what sorts of directions would differently shaped animals use? Would an eight-legged octopus use up, down and then an angle all around since its body is round, or would it have eight directions? How about worms, snakes, and spiders?
14. Why do adolescent mammals play? Do young reptiles play? Do fully-grown individuals play?
15. John C. Wright, in the reference below, describes how two strangers will approach each other without staring directly into each other's eyes so as not to provoke a challenge. They will look at each other and say a greeting only at the moment of passing. He describes how two dogs do the same thing. When they meet, the first to sniff is likely to end up being the dominant one but sometimes both allow the sniff. Compare your techniques for determining friend or foe with that of some other animals. He also says adult dogs ask their friends to play using the same body language that they learned to use while they were puppies. What sort of interactions did you learn as a child? What sort of childhood body language do you use as an adult?
16. What is the benefit for mammals to communicate their inner emotional state–through postures, facial expressions, and vocalizations and such–to other members of their own species and to members of other species? Does it clarify intentions? Is it just to avoid fighting to the death–usually with an animal you cannot even eat–for no good reason? What is the benefit to a rattlesnake when it rattles its tail to give a warning to an approaching animal?
17. Describe the parenting behaviors of rattlesnakes, seahorses, and the Central American Cinote fish, each of which are atypical non-mammalian animals in that they give birth to live young. Compare the number of offspring they have, and the number that survive to adulthood, to those of a related egg-laying species.
18. Describe the reproductive strategies of flat worms, as each individual has both male and female organs.
19. Which emotions do reptiles have even though they do not display them?
20. Can you describe how our lives would be if we didn't have our parent-and-child arrangement? We sometimes hear reports of the breakdown of the nuclear family. Is this happening? Does the nuclear family serve a different purpose today than it had in the past one million years? If so, then why is it occurring and should we do something about it? Is likely that our ancient, biological ancestors first took to forming monogamous parenting relations because the life of their children depended on it. The efforts of both parents were needed or the child would too often die before reaching adulthood. The lives of our children today are at stake only if they take up a life of drugs or crime, but the quality of their lives can be affected by having a single parent. If their lives are no longer at stake, as was the case one million years ago, why do today's children need two parents?
21. Describe motherhood and fatherhood. Explain why the parents of a murderer still love their child and why my friend Nick has "a face that only a mother could love" (when I asked Nick this question he answered "Hey, I resemble that remark").
22. Do parents from every culture act in the same way toward their children? If so then how do they differ, and do the differences amount to 50% or is it about one part in a thousand?
23. How has parenting changed in the last few generations?
24. How do the religions, governments, and businesses of the world view parenthood?
25. Can you make an experiment to see if you can create the circumstances to get a monogamous or harem-forming species to switch its tactics? Is it genetic or learned behavior? Do you want a single spouse because you learned this behavior from your parents or because that behavior is part of your genetic heritage? Do you feel any inkling within you to form a harem? As you fall in love with one person, do you stop noticing all others?
26. A nuclear family of humans simultaneously includes children of various ages. Which other mammalian species have nuclear families or families consisting of siblings, which are children of various ages? How many years does it usually take for mammalian offspring to mature and separate from their parent(s)? What role did language play in our initial development of the nuclear family? How many words and gestures could we make one million years ago?
26. Some species form social groups. How does being social make an individual more likely to live long enough to have offspring?
27. Create a piece of art that explains how you feel about being a mammal or a parent.
28. Which characteristics do you look for in a spouse? Do many persons agree with you? Have people preferred these characteristics through the generations? If so, have the average levels of these characteristics been increasing through the generations? How do we choose preferences? Which characteristics did our Homo habilis ancestors prefer?
29. What do animals do to reduce their population growth when it becomes necessary? How could these measures be useful to individuals and to the species?
30. Do insects sleep? Why do animals sleep? What tells you that it is time to sleep. What happens to our sleeping patterns when we live near in the polar regions of the Earth and have months in which the sun never sets followed by months in which the sun never rises? If you lived for days in a room that had no windows or clock, how would you decide when to sleep? (Studies have found that in this situation, some people will stay awake for three hours and then sleep for one, while others stay awake for two hours every six, and yet others sleep sixteen hours after being awake for forty-eight.)
31. How does the rate of genetic change per generation compare among harem holders, monogamous groups, promiscuous groups, and territorial species who have little choice in mates? How does the level of genetic variability compare among practitioners of these reproductive strategies?
32. How would human mate selection differ if it was based largely on singing and dancing, as it is for birds?
33. Since the members of a species do not fight to the death during conflicts, less there would be no individuals left alive, can war be in the nature of a human or is war different than a conflict between two individuals?
Primary source for the chapter
Social Behavior in Mammals by Trevor B. Poole, Blackie Glasgow and London, 1985 ISBN 0-216-91440-X.
Suggestions for further reading
Animal Behavior An Evolutionary Approach Third Edition, John Alcock, 1984, Sinauer Associates Inc Publishers, Sunderland, MA.
Sociobiology, the Abridged Edition, Edward O. Wilson, 1980, The Belknap Press, Cambridge, Massachusetts.
The Insect Societies, 1971, Edward O. Wilson, 1980, The Belknap Press, Cambridge, Massachusetts.
The Dog Who Would be King, Tales and Surprising Lessons from a Pet Psychologist, John C. Wright with Judi Wright Lashnits, 1999, Rodale Press Inc., Emmaus Pennsylvania.
Sociobiology and Behavior, David P. Barash, 1982, Elsevier, New York.
The Cichlid Fishes, natures grand experiment in evolution, George W. Barlow, 2000, Perseus Publishing, Cambridge, Massachusetts. Barlow describes the parenting behaviors of a monogamous species of fish.
Music, the Brain, and Ecstasy, How Music Captures Our Imagination, Robert Jourdain, 1997, Avon Books, New York.
Music and Miracles, Don Campbell, 1992, Quest Books, Wheaton, Illinois.
The Man Who Mistook His Wife for a Hat, Oliver Sachs, 1985, Touchstone, New York, New York.
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