52 what, how, and why questions what questions focus on the stimuli that elicit a behavior; such...

52 What, How, and Why Questions

• What questions focus on the stimuli that elicit a behavior; such stimuli are the proximate causes of the behavior.

• How questions focus on the development of a behavior and the neural and hormonal mechanisms that underlie a behavior.

• Why questions are concerned with the function and evolution of a behavior; the selective pressures that shape a behavior are considered ultimate causes.

52 Behavior Shaped by Inheritance

• Stereotypic behaviors are performed in the same way every time. If there is little difference in the way different individuals perform the behavior it is said to be species-specific.

• Ex. Web spinning by spiders.

Figure 52.1 Spider Web Designs Are Species-Specific


• Ethologists study the behavior of animals in their natural environments.

• The parallel field of comparative psychology focuses on learning by animals in laboratory environments.

• Central Question: To what extent are behaviors determined by inheritance and to what extent are they modified by experience.


• Deprivation and hybridization experiments were used to determine whether a behavior is inherited.

• In deprivation experiments, animals were raised in conditions the behavior being studied.

• If the behavior was displayed in its entirety, then it was described as inherited.

• Ex. Squirral story.


• In hybridization experiments, closely related species that differ in aspects of a behavior are bred to produce hybrid offspring.

• Konrad Lorenz did hybridization experiments with duck species that can interbreed, but rarely do so because of the specificity of their courtship displays.

• His results showed that motor patterns of courtship displays are inherited.


• Releasers are stimuli that trigger many inherited behaviors.

• Releasers are usually a simple sensory signal. What they see, hear, etc.

• Ex. Herring gulls, bulls.


• Today, behavioral biologists believe that most behaviors develop through an interaction of inheritance and learning.

• For example, begging in herring gull chicks also has a learned component: Over time, gull chicks learn the characteristics of their parents, refine their parental image, and eventually beg only from their own parents.


• Imprinting is a type of learning in which animals learn, during a critical period, a complex set of stimuli that later act as a releaser.

• Lorenz showed that newly hatched goslings imprint on the image of the first object they see (normally their parent, but under experimental conditions, Lorenz or his assistants).

• Subsequent exposure to the object releases the goslings’ following behavior.

Figure 52.5 Imprinting Enables an Animal to Learn a Complex Releaser


• The ability to learn and modify behavior based on experience can change behaviors often.

• In species with non-overlapping generations, opportunities to learn from parents are not available, so inherited behaviors are very important.

Spiders and their webs.


• Inherited behaviors also occur when there are opportunities for learning the wrong behavior, when mistakes would be costly or dangerous.

• The behavior must be performed correctly the first time; there may be no second chance.

Ex. Predator avoidance

52 Hormones and Behavior

• Differences in behaviors of males and females are an example of genetic influence on behavior.

• Action of the sex steroids on the brain determine sex differences in behavior.

• The sexual behavior of rats differs between males and females.

• Receptive female rats display lordosis, a posture in which the hindquarters are slightly raised.

• Male rats, on the other hand, display mounting and copulatory behavior.

52 Hormones and Behavior

• Sex steroids present early in life determine which pattern of sexual behavior an adult rat will display.

Figure 52.7 Hormonal Control of Sexual Behavior (Part 1)

Figure 52.7 Hormonal Control of Sexual Behavior (Part 2)

52 The Genetics of Behavior

• Behavior has genetic determinants. Genes code for proteins; there are then many complex steps between this starting point and the expression of a behavior.

• There is no behavior for which we know the precise series of steps from gene to behavior.

52 Communication

• Communication is behavior that influences the actions of other individuals.

• The displays or signals of communication convey information, and the transmission of this information benefits the sender and the receiver.

• There are five channels of communication: chemical, visual, auditory, tactile, and electric. These channels differ in their effectiveness in different environments.

52 Communication

• Pheromones are molecules used in chemical communication between individuals.

• Pheromones can convey very specific messages with large amounts of information. An example is the pheromone released by female silkworm moths.

• Territory marking by cats and other mammals provides information on the species, individual identity, reproductive status, size, and when the animal was last in the area.

• Pheromones remain in the environment for a while, in contrast to vocal or visual signals.

Figure 52.11 Many Animals Communicate with Pheromones

52 Communication

• The speed of diffusion of pheromone molecules is determined by the size and chemical nature of the molecules.

• Sex attractants tend to be small molecules that diffuse rapidly; such messages travel great distances and quickly disappear.

• Scent marking pheromones tend to be large molecules that create relatively localized, long-lasting messages.

52 Communication

• The advantages of visual signals include ease of production, diversity, flexibility, speed, and a clear indication of the position of the signaler.

• The disadvantages of visual signals include failure to get the attention of the receiver, who may not be focused on the sender, and limitations on the details that can be transmitted.

• Visual communication also works poorly at night and in complex or low-light environments.

52 Communication

• Unlike visual signals, auditory signals can be used at night or low-light environments. In addition, the receiver does not have to be focused on the sender of an auditory signal to get the message.

• Sound can provide directional information as long as the receiver has at least two receptors with some space between them.

• Communicating with sound works well over long distances; an extreme example is the song of humpback whales, which can be heard hundreds of kilometers away.

• However, visual signals are better than auditory signals at rapidly conveying complex information.

52 Communication

• Communication by touch is very common among animals, particularly when conditions are poor for visual communication.

• Studies by Karl von Frisch revealed the role of tactile communication in the dance of honeybees.

• A successful forager returns to the hive and communicates by dancing in the dark on a vertical surface within the hive.

• As she dances, her hivemates monitor her movements through touch and interpret her message.

52 Communication

• If the food source is more than 80 m away, the waggle dance is used to convey information about distance and direction to the food source.

• The round dance conveys information about the distance of food if it is within about 80 m.

• The odor on the bee’s body also provides information about the kind of flower to look for.

Figure 52.12 The Waggle Dance of the Honeybee

52 Communication

• Some fish emit electric pulses and generate electric fields in the water around them. Such signals can be used to detect objects in the environment and to communicate.

• Glass knife fish emit electric signals that convey information about the sex, identity, and position within the dominance hierarchy of the sender.

• Resident individuals adjust the frequencies of their signals to prevent overlap with a new fish introduced into their tank.

52 The Timing of Behavior: Biological Rhythms

• Circadian rhythms are rhythms that are about 24 hours long but do not depend on the cycle of light and dark.

• Animals in constant darkness demonstrate daily cycles of sleep and activity; they are said to have an endogenous (internal) clock.

• A rhythm is a series of cycles and the length of one cycle is the period.

• Any point in the cycle is called a phase; two rhythms that completely match are said to be in phase.

• Rhythms that are shifted so as to be out of phase are described as phase-advanced or phase-delayed.


• Entrainment is the process of resetting the circadian rhythm by exposure to environmental cues.

• Animals in constant light or dark will not be entrained to the 24-hour cycle of the environment; their circadian clock is described as free-running.

• The free-running circadian rhythm is under genetic control.

• Free-running circadian rhythms of animals can be entrained in the laboratory by short pulses of light or dark every 24 hours.

Figure 52.13 Circadian Rhythms


• In mammals, the master circadian clock is located in the suprachiasmatic nuclei (SCN).

• The SCN is found only in vertebrates; in some vertebrates, the SCN is the master clock (mammals), and in others the master clock is the pineal gland (birds).

• In some invertebrates (mollusks), the cells driving circadian rhythms are in the eyes.

• In protists and fungi, rhythmicity is a property of individual cells.

Figure 52.14 Where the Clock Is (Part 1)

Figure 52.14 Where the Clock Is (Part 2)


• The clock genes that regulate circadian rhythms are homologous across a wide range of organisms.

• In fruit flies, the genes period (per) and timeless (tim) are clock genes.

• Mutations of the per gene cause flies to have either short or long free-running circadian periods, and mutations of the tim gene result in loss of circadian rhythms.

• The transcription and translation of these two genes have a circadian rhythm, and the rhythm appears to be controlled by negative feedback of the PER and TIM proteins on two other clock genes, clock (clk) and cycle (cyc).

Figure 52.15 Circadian Rhythms Are Generated by a Molecular Clock


• This molecular negative feedback loop is the basic model for a clock mechanism.

• Genes produce products that shut down their own expression, with a delay.

• The mammalian clock has a similar circuit design and some homologous genes, but their molecular interactions and functions are different.


• Day length, or photoperiod, is a reliable indicator of upcoming seasonal changes. Animal species are described as photoperiodic if their behavior or physiology is influenced by day length.

• Some animals, such as those that hibernate, cannot rely on day length as a cue of upcoming seasonal change and instead have endogenous annual rhythms called circannual rhythms.

• Circannual rhythms are usually shorter than 365 days.

• The neural mechanisms of circannual rhythms are unknown.

52 Finding Their Way: Orientation and Navigation

• Piloting is a simple means of navigation involving the use of landmarks.

• Gray whales use landmarks along the west coast of North America to find their way between the Bering Sea and the coastal lagoons of Mexico.


• Homing is the ability of an animal to return to its nest site or burrow.

• In many animals, homing involves piloting, the use of landmarks in a familiar environment.

• Incredible examples of homing are also found among marine birds that can return home after flying great distances over open ocean with few, if any, landmarks.

• Albatrosses, for example, return to the island on which they were raised after spending 8 or 9 years flying over southern oceans.

Figure 52.16 Coming Home


• In other species, including homing pigeons, individuals released at a location they have never been before can still find their way home.

• Homing pigeons do not fly randomly until encountering familiar landmarks. Instead, they fly in a fairly direct route to their home loft.

• Experiments have shown that these birds can navigate without visual cues from the landscape. Birds fitted with frosted contact lenses so that they could only see the degree of light and dark could still find their way home.


• Seasonal movement between breeding and nonbreeding grounds is called migration.

• Many homing and migrating species are able to take direct routes to their destinations, even through environments they have never experienced before.

• Two types of navigation include distance-and-direction navigation (knowing direction to the destination, and how far it is) and bicoordinate or true navigation (knowing latitude and longitude of current position and destination).


• Experiments with starlings showed that naive juvenile birds were using distance-and-direction navigation.

• Experienced adult birds were not disrupted by geographic displacement.

Figure 52.17 Distance-and-Direction Navigation


• Biological rhythms may be involved in determining distances for some migratory species.

• Birds held in captivity show increased and oriented activity, termed migratory restlessness, at about the time they would normally migrate.

• The duration of migratory restlessness correlates with the typical duration of migration for the species.

• This suggests that the duration of migratory restlessness could set the distance for migration.


• Animals may use the sun and the stars to determine direction.

• The sun is an excellent compass, provided the time of day is known. Animals can determine time of day from their circadian clocks.

• Clock-shifting experiments have shown that birds are capable of using their circadian clocks to determine direction from the position of the sun.


• In a clock-shifting experiment, a bird is placed in a circular cage from which it can see the sun and sky but no other visual cues.

• After training the bird to expect food from a certain direction, scientists were able to phase-advance the bird’s circadian rhythms by 6 hours. Once under normal conditions, the bird looked for food in the wrong direction.

• These birds are using a time-compensated solar compass.

Figure 52.18 The Time-Compensated Solar Compass (Part 1)

Figure 52.18 The Time-Compensated Solar Compass (Part 2)


• Many species are active at night, or simply migrate at night, and thus cannot use the sun for directional information. These species appear to use stars for direction.

• Species that rely on stars for directional information can use the North Star, a fixed point that always indicates north, or constellations, collections of stars that move as Earth rotates.

• Animals need to use their circadian clock with the moving constellations.


• Stephen Emlen tested the orientation abilities of birds in a planetarium in which the star patterns were projected on the domed ceiling. The star patterns could be rotated to simulate rotation of Earth.

• Wild-caught birds could orient in the planetarium when the star patterns were either stationary or rotated more quickly than normal.

• These results showed that the birds were using the North Star, the fixed point in the sky, for directional information, rather than the constellations.


• Birds raised in the planetarium under a stationary sky and tested with a stationary sky could not orient well.

• However, birds raised in the planetarium under a rotating sky oriented well when tested with a rotating sky.

• Thus, birds could learn to use constellations for orientation as long as the sky rotated during the time the birds were maturing.


• Use of the sun and stars for directional information is not possible during overcast conditions.

• Some birds, such as pigeons, can orient well under overcast skies, apparently using their ability to sense Earth’s magnetic field and thus gain directional information.

• When small magnets were attached to the heads of pigeons and the birds were displaced under overcast skies, they could not find their way back to their home loft.


• It now appears that homing pigeons use the sun when available, magnetic cues when the sun is unavailable, and landmarks when close to home.

• There appears to be considerable redundancy in the means by which animals determine direction.

• Other sources of directional information include the plane of polarized light, low-frequency sound, and weather patterns.

52 Human Behavior

• Culture is the transmission of learned behavior from one generation to another and is characteristic of humans.

• Human behavior is also influenced by genetic factors.

• Some motor patterns appear to be programmed into the human nervous system.

• For example, similar facial expressions are displayed by human populations that have had little or no contact. Blind infants smile and frown although they have never seen these expressions in others.

52 Human Behavior

• As we acknowledge that human behavior has both learned and genetic components, we also find examples of culture, once thought to be a uniquely human characteristic, in other animals.

• Japanese macaques, for example, developed new methods of food preparation, and these methods were transmitted to other individuals in the population via imitative learning.

• Chimpanzees also display culturally transmitted behaviors including tool using and courtship. Populations have distinct behavioral repertoires or culture.

52 what, how, and why questions what questions focus on the stimuli that elicit a behavior; such...

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