Animal Culture: Group Learning Flashcards
Cultural Transmission
What Is Cultural Transmission?
• What’s So Important about Cultural Transmission?
• Effects of Others on Behavior
• Social Learning
• CONSERVATION CONNECTION: Crop Raiding, Elephants, and Social Learning
There is now a growing recognition of the importance of the cultural transmission of behavior—typically defined as the transfer of information from individual to individual through social learning or teaching—both within and between generations of animals.
WHAT’S SO IMPORTANT ABOUT CULTURAL TRANSMISSION?
We spent a great deal of time on the topic of learning in chapter 5, and if cultural transmission is just one form of learning—that is, learning from other individuals—why not simply consider it a special kind of learning and move on? Why not think of cultural transmission as just another means by which organisms adapt to the environment? The answer to these questions is that learning from other individuals involves the spread of information from individual to individual: information can be spread through a population.
This potentially translates into the behavior of a single individual in a population dramatically shifting the behavior patterns seen in an entire group—recall how the new behaviour of Imo’s ( a Japanese macaque) novel food-washing techniques spread via cultural transmission. This is not the case for other types of learning. What an individual learns via individual learning disappears when that individual dies, and perhaps earlier.
When cultural transmission is in play what is learned by one individual may be passed down through generations. If Imo had learned to clean her sweet potatoes by washing them in water in a population in which social learning was absent, this foraging innovation would have vanished when she died. Instead, decades later, one can still go to Koshima Islet and see monkeys washing their sweet potatoes.
Cultural transmission can spread behaviors throughout a population very quickly, which makes it a particularly potent form of information transfer. When natural selection acts to change the frequency of genes
that code for behavior, the time scale can range from a few dozen generations (as in the guppy case we explored in chapter 2) to much longer time scales (thousands of generations). And when natural selection acts on major morphological change, the time scale may be even longer.
Cultural transmission of information, on the other hand,
operates much faster, and can cause important changes in the behavior seen in populations in just a few generations. In fact, cultural transmission can have a dramatic impact within a single generation (Boyd and Richerson, 1985, 2004, 2005; Henrich et al., 2005; OdlingSmee et al., 2003; Reader and Laland, 2003).
EFFECTS OF OTHERS ON BEHAVIOR
Cultural transmission involves a “model” individual—sometimes called a demonstrator or tutor—and an “observer,” who learns a specific action or series of actions from the model. But there are situations that involve an interaction between observers and models, but that do not constitute social learning or teaching. In these cases—labeled local enhancement and social facilitation—the observer is drawn to an area by a model or by the action of a model, or is simply in the presence of models, but the observer does not learn a particular behavior or response from the model, so cultural transmission is not occurring.
Local Enhancement:
William Thorpe coined the term local enhancement to describe the situation in which individuals learn from others, not so much by doing what they observe, as by being drawn to a particular area because another individual—a model—was in that location (Heyes, 1994;
Thorpe, 1956, 1963). In other words, a model simply
draws attention to some aspect of the environment by the action it undertakes there (for example, digging for worms). Once the observer is drawn to the area, the observer may learn on its own, via individual learning.
Consider foraging behavior in colonially nesting cliff swallows, birds that feed in groups ranging in size from 2 to 1,000 individuals (see chapter 2). Charles Brown has found that, in addition to the actual transfer of information between groupmates (C. R. Brown, 1986), local enhancement facilitates foraging, as some individuals are drawn to good foraging areas just because other birds are foraging there.
Social Facilitation:
Social facilitation differs in a subtle, but important, way from local enhancement. During local enhancement, the action of a model draws attention to some aspect of the environment. But under social facilitation, the mere presence of a model, regardless of what it does, is thought to facilitate learning on the part of an observer (Zajonc, 1965). For example, there are many instances in the foraging literature in which increased group size caused increased foraging rates per
individual, perhaps because the mere presence of others made them safer (Giraldeau and Caraco, 2000; Stephens and Krebs, 1986).
Social facilitation and local enhancement can be experimentally separated from one another. To see how, we can discuss Elisabetta Visalberghi and Elsa Addessi examining what factors affected a capuchin monkey’s probability of eating a novel food. In treatment I, a lone capuchin was tested on its tendency to try a new food type (vegetables that had been color dyed). In treatment II, a capuchin and the novel food type were on one side of a test cage, and a group of
capuchins was on the other side of the cage.
No food was placed on the side of the cage with the group. Treatment III was identical to the second, except that a familiar food type was placed on the side of the
cage with the group, which made it likely that they would eat the food. Now the lone capuchin saw not only a group, but a group that had individuals eating food, just not the novel food. These treatments were carefully designed to create potential for social
facilitation (treatment 2: mere presence of others) and local enhancement (treatment 3: presence of others that are eating). Treatment 1 served as the control condition.
When comparing across their treatments, Visalberghi and Addessi found evidence of local enhancement, but not of social facilitation. Evidence for local enhancement was uncovered in that the test
capuchin in treatment 3 (test capuchin + group with food) was more likely to be eating food than capuchins in treatment 1 (test capuchin alone). Local enhancement was occurring as the test capuchin’s
attention was drawn to the novel food when it saw the other capuchins eating food, and then the test capuchin proceeded to eat more itself. However, no evidence for social facilitation was uncovered.
SOCIAL LEARNING
Social learning, sometimes referred to as “observational learning,” can take many forms in both humans and nonhumans. Below we examine two forms of social learning: imitation and copying.
Imitation:
George Romanes was one of the first psychologists to suggest that cultural transmission via imitation plays an important role in animal societies (Romanes, 1884, 1889, 1898). Since Romanes wrote his books on this subject more than a century ago, the term imitation has
been used in many different ways in the psychological literature (R. W. Byrne, 2002; Heyes and Galef, 1996; Miklosi, 1999; Whiten, 1992). Here, we will adopt Cecilia Heyes’s definition of imitation as the “acquisition of a topographically novel response through observation of
a demonstrator making that response” (Heyes, 1994).
To demonstrate imitation, there must be some new behavior learned from others, and that behavior must involve some sort of new spatial (topographic)
manipulation as well as lead to the achievement of some goal (Figure 6.16). We have already touched on a case of imitation at the start of this chapter. When Imo washed her sweet potatoes in water before she
ate them, and others in her group observed and then learned this novel behavior, which requires a new sequence of spatial actions, imitation was taking place.
A second example of imitation involves milk bottle opening in birds. In the mid-twentieth century, Brits had their milk delivered to their front porches in bottles with foil caps. While seen in many species, this behavior was most common in blue tits (Parus caeruleus) (Figure 6.17). In 1949, Fisher and Hinde circulated a survey to 200 members of the British Ornithological Society
regarding this behavior (Fisher and Hinde, 1949). From this survey, they pieced together the history of the spread of this novel behavior over a large range of Great Britain.
They found that individuals in all the species opening milk bottles, including blue tits, rarely move more than 10–15 miles from their natal habitat, and so “it would seem, therefore, that new centres and records more than fifteen miles distant from any place where the habit has been recorded previously probably represent new discoveries by birds” (Fisher and Hinde, 1949). Fisher and Hinde suggested that this new behavior is, on occasion, accidentally stumbled upon by a lucky blue tit and that others learned this nifty trick, at least in part, from watching the original milk thief (Fisher and Hinde, 1949), thus explaining the wide distribution of the behavior.
Some evidence supports this hypothesis. Milk of different grades in Britain at this time had different colored foil covers. Birds in an area where milk bottles were opened tended to prefer the same color foils,
consistent with the idea that they imitated one another. Which cover foil was preferred varied across a tit population, which is again consistent with cultural transmission via imitation
Imitation raises a number of interesting questions. For example, when individual 1 attempts to imitate individual 2, it can only see individual 2’s movements, but not the muscle activation underlying such
movements. So how does individual 1 know what to do to make such movements itself? This is referred to as the correspondence problem (Brass and Heyes, 2005). Another issue associated with imitation is that of “perspective taking.”
Suppose, for example, that you and I are facing one another, and I raise my right hand and move it in circles. If you wish to imitate this action, you need to take into account our positions relative to one another. If you simply raise the hand that was on the same side as the hand I raised, you would be raising your left
hand, and not precisely imitating my action. Behavioral neuroscience is beginning to shed light on both
correspondence and perspective-taking problems (Rizzolatti et al., 2006).
Studies on these questions in humans often involve subjects who are placed in a magnetic resonance imaging (MRI) device and given some problem to solve while activity in their brain is scanned by the MRI machine. Typically, the problem is very simple—for example, tapping a specific finger a set number of times, or repeating a particular musical chord on the guitar. These studies indicate that certain sections
of the brain—the inferior frontal gyrus, the dorsal and ventral premotor cortex, as well as other areas—are consistently active during imitation.
Interestingly, our brains respond more strongly to opportunities to imitate an action when we see another human doing it than when we see the same action being performed by a robot (Kilner et al., 2003; Tai
et al., 2004). There is less behavioral neuroscience work on these issues in nonhumans, but that is changing (Rizzolatti and Fogassi, 2014; Ferrari and Rizzolatti, 2014). For example, work on imitation in monkeys has found that a set of “mirror” neurons in the F5 area of the premotor area of the monkey brain becomes very active when a monkey observes an
action—such as grasping a piece of food on a tray—and then repeats that action (Molenberghs et al., 2009; Rizzolatti and Craighero, 2004; Rizzolatti et al., 2001).
What makes the mirror neurons in the F5 area
of the brain particularly relevant is that some of these neurons are motor neurons (neurons that are needed to repeat an act during imitation) and some are visual neurons (neurons that are necessary for watching a model). An action must first be observed before mirror
neurons will fire, again suggesting a connection to imitation. Indeed, these neurons will fire if an individual sees a hand manipulating an object, but not if it sees the object alone or if it sees the object being
manipulated by a tool (Gallese et al., 1996; Molenberghs et al., 2012; Rizzolatti et al., 1996).
Some evidence suggests that mirror neurons in humans also reside in the equivalent of the F5 section of our brain, and that such neurons are involved in human imitation as well, but much work in this area remains to be done.
Copying:
When animals copy one another, an observer repeats what it has seen a model do. Typically, the copier is then rewarded for whatever behavior it has copied. In the psychological literature, the rewards associated with copying can be extrinsic (the food items in the above case) or intrinsic (related to animal emotions and feelings). Copying differs from imitation in that what is copied need not be novel and need not involve learning some new topographical action—an individual can copy the action of another, even if it already knows how to do what the model is doing, and even if it does not involve learning some new spatial orientation to do what the model does.
animals will select a mate in the absence of the opportunity to copy the mate choice of others, but, when the opportunity to copy others arises, they may opt to mate-choice copy. Some evidence of copying comes from my own work on mate-choice copying, during which a female copies the choice of those around her. I examined female mate-choice copying in guppies (Poecilia reticulata) using a ten-gallon aquarium situated between two separate end chambers constructed of clear Plexiglas (Dugatkin, 1992b).
A single male was put into each of these end chambers. The observer female— the individual that potentially copies the behavior of other females—
was placed in a clear canister in the middle of the central aquarium. At the start of a trial, one male was put into each end chamber (Figure 6.19). Removable glass partitions created left or right sections of the
aquarium into which another female—the model female—was placed. To rule out the possibility that one male may have been more attractive than the other and that the model and the observer independently each
chose that male, the placement of the model—either near the male in the left end chamber or near the male in the right end chamber—was determined by the flip of a coin.
Once the model, the observer, and the two males were in place, fish were given ten minutes during which the observer female could watch the model female near one of the two males. The model female and the glass partitions were then removed, and the observer female was released from her canister and given ten minutes to swim freely and choose whichever male she preferred. In these trials, the observer female chose the male that had been chosen by the model female
seventeen out of twenty times. While the results of this experiment are consistent with the hypothesis that females copy the mate choice of others, there are
several alternative explanations.
Guppies live in social groups (schools of fish), and so it is possible that the observer female was simply choosing the area that had recently contained the largest number of fish (in this case, two). A control treatment was conducted to test this schooling hypothesis. It was identical to the above protocol, except that females were placed in the end chambers. In this case, the observer female chose the female in the end chamber closest to the model in only ten out of twenty trials.
The tendency to school (stay near two fish rather than one fish) per se does not explain the results of the first
experiment; if it had, observer females would have consistently chosen the end chamber closest to where the model had been placed. Results from other control experiments were also consistent with mate-choice
copying. Using a protocol similar to that of the guppy experiments, mate-choice copying has also been observed in a number of different species of fish, as well as in some birds and mammals (see chapter 7).
Copying also plays a role in the fear response of mice to stable flies (Stomoxys calcitrans; Kavaliers et al., 1999, 2001). Normally, mice that have been exposed to stable flies do not show any immediate behavioral response to the presence of a stable fly. After an individual has been bitten by a stable fly, one of its defensive responses is to bury itself under whatever debris it can find (Figure 6.20). When a naive mouse observes another mouse being bitten by a fly and then burying itself, the observer quickly buries itself when it is exposed to a fly for the first time—it copies the defensive action of the model.
To better understand the underlying molecular genetics of copying and the fear response in mice, Martin Kavaliers and his colleagues focused on the NMDA receptor, a receptor which plays an important
role in neural plasticity (Kavaliers et al., 2001). When Kavaliers and his colleagues blocked the NMDA receptor of an observer mouse, using an NMDA antagonist chemical, they found that the observer did not learn to bury itself as soon as it was exposed to a fly; the NMDA antagonist blocked copying in these mice. A similar experiment with rats that could
copy a model’s foraging behavior also found that blocking the NMDA receptor impeded copying (M. Roberts and Shapiro, 2002).
CONSERVATION CONNECTION
Crop Raiding, Elephants, and Social Learning
Around the world, humans cultivate crops in areas that have not historically been used for agriculture. This can cause conflict between indigenous people and native wildlife that attempt to forage on such crops. For example, around the Amboseli National Park in Kenya, approximately one out of three adult male elephants that have dispersed from their natal groups raid crop fields (Figure 6.15). Raiding crop fields is a dangerous behavior for male elephants, as many are injured or killed by farmers during such raids (Obanda et al.,
2008).
Elephants live in complex social networks, in which both individual and social learning play important roles (Lee et al., 2011; Plotnik et al., 2011; Goldenberg et al., 2014). Patrick Chiyo and his colleagues tested the
hypothesis that male elephants learn how to raid crops—and especially how to be vigilant for farmers when doing so—through some form of social learning (Chiyo et al., 2012). They predicted that males that associated with others that raided crops would raid crops at a higher rate than males that associated with others that did not raid crops and that this effect would be
strongest when males associated with older associates that raided crops, because such associates would likely be the best models.
Chiyo and his team tested their idea in a population of 1,400 elephants— recognizable by unique tusk and body markings—in the Amboseli National Park. They observed fifty-eight male elephants often enough to rank these individuals in terms of their association patterns and were also able to gather information independently on the crop-raiding behavior of these individuals. As predicted, a male was more likely to raid crops if the individual it associated with most often was a crop raider: this was also true when its second-closest associate was a crop raider, but not if only a third, fourth, or more distant associate was a crop raider.
Also, as predicted by Chiyo and his colleagues, this effect was most pronounced when associates were older. One of the long-term goals for ethologists involved in such projects is to guide policy makers in the difficult task of developing management practices
that simultaneously minimize harm to animals and maximize crop productivity. Much work is being done to develop ideas on this front, but one application from the study on social learning in elephants might be something like this: If a plan were developed for providing elephants an alternative food source so that crop raiding is decreased, then this plan should first target older males that serve as models for others in their group.
What Is Cultural Transmission?
• The Rise and Fall of a Tradition
• Teaching in Animals
• COGNITIVE CONNECTION: Parents Teaching Embryos?
THE RISE AND FALL OF A TRADITION
If a new behavior emerges, and then becomes common within a group as a result of social learning, it is referred to as a tradition (Thornton and Clutton-Brock, 2011). In 2009, Alex Thornton and Aurore Malapert ran one of the first controlled experiments on traditions in wild populations, using nine groups of meerkats (Suricata suricatta) in the South African Kalahari (Thornton and Malapert, 2009b; see Thornton and Malapert, 2009a and Thornton et al., 2010).
What is the research question? Can researchers introduce new traditions into animal populations? If so, do the traditions persist?
Why is this an important question? Experimental manipulation of culturally transmitted behavior in natural populations opens the door to future work that focuses on causality.
What approach was taken to address the research question? To experimentally examine traditions, Thornton and Malapert created two different foraging-related traditions which were introduced into a series of great tit populations to study whether traditions established themselves via social learning, and then persisted.
What was discovered? Birds copied the new behavior introduced into their population, and the behavior spread quickly. New traditions persisted across
generations, and did so despite much population turnover.
What do the results mean? Animal behaviorists now have a powerful new approach to examining cultural transmission in wild populations.
TEACHING IN ANIMALS
The idea that animals teach one another is one of the more contentious in the literature on animal cultural transmission. While there are many definitions of teaching, most have one individual serving as an instructor or teacher, and at least one other individual acting as a student who learns from the teacher.
In an early review on teaching in animals, Tim Caro and Marc Hauser suggested that for a behavior to be labeled as “teaching,” a teacher must provide an immediate benefit to students but not to him- or
herself, “students” must be a naive to what is being taught, and a teacher must impart some new information to students faster than they would otherwise receive it.
This definition is interesting, not only because of the emphasis on what must take place for teaching to
occur, but also for what kinds of behaviors are excluded from the realm of teaching. For example, in the case of the blue tits opening the foil caps of milk bottles in Britain in the 1940s, imitation rather than
teaching was taking place. While blue tits learned how to open foil caps by observing others, those that opened the caps did so regardless of who watched them. According to Caro and Hauser’s definition, they
weren’t teaching other birds anything since they opened the milk bottles in the same way even if they were alone and thus they weren’t modifying their behavior only in the presence of naive observers.
They were obtaining immediate benefits for themselves in that they obtained the milk after they opened the bottles. What sort of examples might fall under the Caro and Hauser definition of teaching? Consider a female cat that captures live prey and allows its young to interact with this prey, making sure that the prey doesn’t escape along the way. If mother cats engage in this behavior only when in the presence of young cats, then teaching may be occurring.
Anecdotal examples of this kind of teaching have been documented in domestic cats, lions, tigers, and otters. Teaching has been examined in more detail in both cheetahs and meerkats. Consider Caro’s description of three ways that mother cheetahs used “maternal encouragement” to facilitate hunting skills in their offspring (Figure 6.24):
- Firstly, they pursued and knocked down the quarry but instead of suffocating the victim allowed it to stand and run off. By the time the prey had risen, the
cubs had normally arrived. - Second, mothers carried live animals back to their
cubs before releasing them, repeatedly calling (churring) to their cubs. - Third, and less often, mothers ran slowly during their initial chase of a prey and allowed their cubs to overtake them and thus be the first to knock down the
prey themselves. (Caro, 1994a, pp. 136–137)
While this sort of behavior is consistent with teaching, it is not sufficient to demonstrate teaching, as it is unclear whether young cheetahs accelerated their hunting skills as a result of these interactions with their mother or for other reasons (Caro and Hauser, 1992; Galef et al., 2005; Thornton and Clutton-Brock, 2011). Teaching has been documented in meerkats, where young pups are incapable of catching their own prey. At about a month old, pups begin following groups of foragers, and are assisted in their own foraging attempts by older “helpers” (Figure 6.25).
Many of the prey that meerkats eat are difficult to catch and, in the case of scorpions, are also dangerous. Helpers will often incapacitate scorpions by removing
their stingers and present them to pups as food. Thornton and McAuliffe observed that very young pups were fed either dead or incapacitated scorpions, but as the pups got older, the helpers presented them more and more often with live scorpions (Thornton and
McAuliffe, 2006).
To experimentally examine whether helpers were teaching pups how to forage on dangerous prey, the researchers took advantage of the fact that helpers respond to the begging calls of pups even when pups
cannot be seen, and that such begging calls change in predictable ways as pups age. When Thornton and McAuliffe had a group of young pups, but played the calls of older pups, helpers were more likely to
bring live prey over to the pups.
When the group contained older pups, but the researchers broadcast the begging calls of younger pups, helpers were more likely to bring over dead or incapacitated scorpions: helpers were changing what type of prey they delivered in a manner that would help and might even teach the pups. Thornton and McAuliffe found additional evidence for teaching by
helpers in that helpers:
(1) spent much time monitoring pups after presenting them with food;
(2) retrieved prey when pups lost their food;
(3) on occasion, further modified a scorpion (removing the stinger, killing the scorpion, and so on) after it was lost but later retrieved by the pups; and
(4) nudged pups that were reluctant to eat scorpions, increasing the probability that the pups would eat the scorpion that they had initially rejected.
Together, the evidence suggests teaching in that
helpers modified their behavior in costly ways—spending time that they could have used to forage for themselves but instead spent with pups— and such modifications helped pups learn how to forage on dangerous prey.
Common Themes in Examples of Animal Teaching:
Caro and Hauser, as well as subsequent researchers, found two common themes in nonhuman teaching -
- First, almost all instances of animal teaching focus on the parent/offspring relationship. suggest something special about the costs and benefits of teaching in the parent/teacher, offspring/student relationship. The benefits associated with the genetic kinship that bonds teacher and student—that is, parent and offspring or perhaps between siblings—may be some of the only
benefits large enough to make up for the costs of teaching (Caro and Hauser, 1992; Galef et al., 2005).
- Second, cases of teaching tend to fall into one of two categories: “opportunity teaching” and “coaching.” In opportunity teaching, teachers actively place students where they can learn a new skill. In contrast, coaching involves a teacher who directly alters the behavior of students by encouragement or punishment. The majority of examples of animal teaching fall under opportunity teaching, presumably because this type
of teaching is the simpler of the two. The meerkat example, however, shows nicely how both forms of teaching can be in play in the same system. Meerkats use opportunity teaching by manipulating prey for
young pups, while at the same time coaching pups by nudging them and thereby encouraging them to try new, potentially dangerous, food items.
Modes of Cultural Transmission
• Vertical Cultural Transmission
• Oblique Cultural Transmission
• Horizontal Cultural Transmission
VERTICAL CULTURAL TRANSMISSION
Vertical cultural transmission occurs when information is transmitted across generations from parent(s) to offspring. This type of cultural transmission might take place through either teaching or social learning
—offspring might learn from their parents by observation, or parents might teach a behavior to their offspring. For example, in some finch species, vertical transmission occurs when males learn the song that
they will sing from their fathers, as well as when females develop song preferences in potential mates based on the songs their father sang (B. R. Grant and Grant, 1996; Figure 6.28).
Oblique cultural transmission refers to the transfer of information across generations, but not via parent/offspring interactions: young animals get information from adults that are not their parents. This sort of transmission might be particularly common in systems where there is no parental care, and hence where most interactions between younger and older individuals would be between nonrelatives.
Horizontal cultural transmission involves transmission between peers—same-aged individuals—and occurs not only in adults but young individuals as well. Consider the case of horizontal transmission of foraging-related information in guppies. Laland and Williams trained same-aged guppies to learn different paths to a food source—a long path and a short path (Laland and Williams, 1998). Laland and Williams found that in both the short-path and long-path groups, guppies at the end of the experiment still followed the path to which the original fish had been trained. Horizontal transmission of information was operating, as the only models from which to learn were same-age individuals.
The Interaction of Genetic and Cultural Transmission
• Finch Song
• Guppy Mate Choice
Cultural Transmission and Brain Size
FINCH SONG
Peter and Rosemary Grant have been studying finches in the Galápagos Islands for more than three decades. Among the many problems they have tackled is the role of cultural transmission in the evolution of finch song. In Galápagos finches, cultural transmission not
only shapes birdsong but it interacts in an unexpected manner with the genetics of reproductive isolation and speciation in these birds (P. R. Grant and Grant, 1994, 1997).
The medium ground finch (Geospiza fortis) and the cactus finch (G. scandens) both live on the Galápagos island of Daphne Major. Although these are classified as different species, some cases of interbreeding between these two finch species have been uncovered, and the hybrids do not appear to suffer a decrease in reproductive success as compared to the matings within species. Yet although there seems to be no cost for hybridization, medium ground finches
and cactus finches rarely interbreed. Why? Does cultural transmission play a role in inhibiting such interbreeding (Freeberg, 2004; Lachlan and Servedio, 2004; D. A. Nelson et al., 2001; Slabbekoorn and Smith,
2002)?
In finches, males learn the songs they sing. When the Grants studied the songs sung by ground and cactus finches during the mating season, they found that these songs were transmitted across generations via cultural transmission (B. R. Grant and Grant, 1996). Fathers and sons have very similar songs, but this could be due to
genetic transmission from father to son, or it could be due to the cultural transmission of the song from father to son. If songs are genetically controlled, then the songs of sons and their paternal and maternal grandfathers should be similar, since they inherit genes from both grandfathers.
But if the songs are culturally transmitted from father
to son, then the songs of the sons should resemble only those of their paternal grandfather, but not those of their maternal grandfather. This is because the paternal grandfather would have transmitted the song to the father, who would then have transmitted the song to the son. The evidence suggests that the songs of sons resemble the songs of their paternal grandfathers, but not the songs of their maternal grandfathers (Figure 6.32). Birdsong in these finches appears to be culturally transmitted.
The Grants also found that the songs of ground and cactus finches were different from one another. These differences in their songs—a culturally transmitted trait—have a dramatic impact on gene flow across species. Of 482 females sampled, the vast majority (over
95 percent) mated with males who sang the song appropriate to their own species, that is, cultural transmission of song allows females to recognize individuals of their own species. In addition, females tend to avoid males who sing songs that are similar to the songs that their own fathers sang, which suggests that song also plays a role in preventing inbreeding.
Because song is culturally transmitted from father to son, females may decrease the probability of mating with genetic relatives when they avoid mating with males that sing like their fathers. In their long-term study, the Grants uncovered eleven cases in which
the male of one species sang the song of another species. In most of these cases, cross-species breeding would then occur, resulting in hybrid offspring; remove the normal pattern of cultural transmission and the barrier to breeding across species disappears, suggesting a new and exciting avenue of research in the interaction of cultural transmission and genetics.
GUPPY MATE CHOICE
female guppies copy the mate choice of other females. Observer females that viewed a model female choose one male over another were much more likely to choose that male themselves. In addition to this type of cultural transmission of information, genetic transmission of traits also plays an important role
in guppy mate-choice (Houde, 1997; Magurran, 2005).
Guppies from the Paria River in Trinidad and Tobago prefer to mate with orange-colored males.
Interpopulational comparisons suggest that
this preference of Paria River females for males with more orange body color is heritable (Houde, 1988; Houde and Endler, 1990). In addition, orange body color itself is a heritable trait in Paria River males (Houde,
1992, 1994). To examine how genetic and cultural transmission interact in shaping mate choice in females from the Paria River, I set up an experiment
with four different treatments (Dugatkin, 1996b). In each treatment, a female was exposed to a pair of males.
Results of the experiment suggest that females in treatment I—in which males were matched for orange body color—copied each other’s mate choice. When males differed in orange body color by an average
of 12 or 24 percent (treatments II and III, respectively), females consistently preferred the less orange of the two males, again copying the mate choice of the model female; in these treatments, culturally transmitted information overrode a female’s genetic predisposition to mate with males with lots of orange body color.
But when male orange body color differed by an average of 40 percent (treatment IV), females consistently preferred the more orange of the two males, thus overriding any effects of mate-choice copying (Figure 6.33). In the guppy system, it appears that whether or not females copy a model’s mate choice is affected by a threshold difference in the amount of orange body color in the male.
Cultural Transmission and Brain Size:
Many ethologists have suggested that in a population of large-brained animals, new innovations—the discovery of novel solutions to problems —might arise and spread more often than would happen in a
population of small-brained animals. In the most comprehensive study to date, Simon Reader and Kevin Laland found that across more than 100 species of nonhuman primates, there was a significant positive
correlation between brain size and both innovation and tool-use frequency, confirming the predicted trends (Dunbar, 1992; Reader and Laland, 2002; Sawaguchi and Kudo, 1990).
Reader and Laland defined innovations as “novel solutions to environmental or social problems.” They uncovered 533 recorded instances of innovations, 445 observations of social learning, and 607 episodes of tool use that covered 116 of the 203 known species of
primates. and mapped out these behaviors against “executive brain” volume, a measure that includes both the neocortex and striatum sections of the brain (Jolicoeur et al., 1984; Keverne et al., 1996).
Innovation, social learning, and tool use all had a positive correlation with the absolute value of executive brain volume (Figure 6.34). A similar trend between large brain size and an increased propensity toward innovation was found for birds in North America, Britain, and Australia (Lefebvre et al., 1997a; Lefebvre et al., 1997; Lefebvre et al., 2004; Sol, Lefebvre et al., 2005). This relationship has interesting implications for questions relating to the conservation and ecology of
birds (Overington et al., 2011; Sol, Duncan et al., 2005; Sol, Lefebvre et al., 2005; Sol et al., 2010; Sol et al., 2016).
For example, Daniel Sol and his team examined whether the relationship between brain size and innovation affected bird species when they were moved to novel environments through large-scale, human “introduction” programs (where humans introduce a new species to a novel habitat). Using data
on more than 600 such introduction programs around the world, Sol and his colleagues found that bird species in which individuals had a high brain size/body ratio were more likely to survive and thrive (that is,
to have greater “invasion potential”) after introduction to novel environments than were species with lower brain size/body ratios.
In addition, the researchers found that when large-brained species were introduced to novel environments, they increased their rate of innovation—for example, by using a new foraging technique—which in turn increased their probability of success (their “invasion potential”) in their new habitats (Box 6.5).
