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Introduction
Cultural transmission, also known as cultural learning, is defined as the process and method of passing on socially learned information. Within a species, cultural transmission is greatly influenced by how adults socialize with each other and with their young. Differences in cultural transmission across species have been thought to be largely affected by external factors, such as the physical environment, that may lead an individual to interpret a traditional concept in a novel way. The environmental stimuli that contribute to this variance can include climate, migration patterns, conflict, suitability for survival, and endemic pathogens. Cultural transmission is hypothesized to be a critical process for maintaining behavioral characteristics in both humans and nonhuman animals over time, and its existence relies on innovation, imitation, and communication to create and propagate various aspects of animal behavior seen today.

Definition
Culture is defined as “all group- typical behavior patterns, shared by members of animal communities, that are to some degree reliant on socially learned and transmitted information”. Additionally, culture is not passed on genetically from parents to offspring, but rather learned through experience and participation, which makes the evolution of cultural transmission greatly reliant on intra-species traditions. The likelihood of larger groups within a species developing and sharing these intra-species traditions with peers and offspring is much higher than that of one individual spreading some aspect of animal behavior to one or more members. This is why cultural transmission has been shown to be superior to individual learning, as it is a more efficient manner of spreading traditions and allowing members of a species to collectively inherit more adaptive behavior. This process by which offspring within a species acquires his or her own culture through mimicry or being introduced to traditions is referred to as enculturation. The role of cultural transmission in cultural evolution, then, is to provide the outlet for which organisms create and spread traditions that shape patterns of animal behavior visible over generations.

Dawkins’s Meme Theory
Evolutionary biologist Richard Dawkins made groundbreaking headway into the field of cultural transmission with his 1976 book entitled The Selfish Gene, which focused heavily on the move to evolution being understood primarily by genetic influence. Dawkins coined the term meme, the primary unit of cultural transmission or imitation, to explain an overarching mechanism of how animal behavior is shared and spread to lead to cultural evolution. The use of the word meme was an intentional phonetic derivation of the similar sounding word “gene”, which Dawkins asserts to be the primary unit of selection as it lends itself to pathways of biological evolution:

“We need a name for the new replicator, a noun that conveys the idea of a unit of cultural transmission, or a unit of imitation.’Mimeme' comes from a suitable Greek root, but I want a monosyllable that sounds a bit like 'gene'. I hope my classicist friends will forgive me if I abbreviate mimeme to meme. (Dawkins)”

The analogy between the gene and meme proposed by Dawkins as units of evolutionary biology serves to reinforce the idea that there is a particular pathway of transfer associated with each unit that lends itself either to the evolution of genotypic, phenotypic, and/or behavioral patterns within animal groups. Dawkins asserts that in order for cultural evolution to take place, there needs to be (1) variation within the memes present, (2) the capacity for meme replication between two or more parties, and (3) fitness advantages and/or disadvantages with each meme that lead to the selection or rejection of one meme over another. Likewise, these three criteria in the context of genes are also necessary for genetic evolution. However, with the meme unit, cultural transmission has a distinct feature of being capable of taking place by individuals developing varying interpretations of the meme without exactly “copying” it to pass it on. These interpretations lead to the creation of new memes, which are themselves subject to a cyclic process of selection, rejection, or modification.

Whiten’s “Culture in Chimpanzees”
Andrew Whiten, professor of Evolutionary and Developmental Psychology at the University of St. Andrews, contributed to the greater understanding of cultural transmission with his work on chimpanzees. In Cultural Traditions in Chimpanzees, Whiten created a compilation of results from seven long-term studies totaling 151 years of observation analyzing behavioral patterns in different communities of chimpanzees in Africa (read more about it below). The study expanded the notion that cultural behavior lies beyond linguistic mediation, and can be interpreted to include distinctive socially learned behavior such as stone-handling and sweet potato washing in Japanese macaques. The implications of their findings indicate that chimpanzee behavioral patterns mimic the distinct behavioral variants seen in different human populations in which cultural transmission has generally always been an accepted concept.

Cavalli-Sforza & Feldman Models
Population geneticists Cavalli-Sforza & Feldman have also been frontrunners in the field of cultural transmission, describing behavioral “traits” as characteristics pertaining to a culture that are recognizable within that culture. Using a quantifiable approach, Cavalli-Sforza & Feldman were able to produce mathematical models for three forms of cultural transmission, each of which have distinct effects on socialization: vertical, horizontal, and oblique.


 * Vertical transmission occurs from parents to offspring and is a function which shows that the probability that parents of specific types give rise to an offspring of their own or of another type. Vertical transmission, in this sense, is similar to genetic transmission in biological evolution as mathematical models for gene transmission account for variation. Vertical transmission also contributes strongly to the buildup of between-population variation.
 * Horizontal transmission is cultural transmission taking place among peers in a given population. While horizontal transmission is expected to result in faster within-group evolution due to the relationship building between peers of a population, it is expected to result in less between-group variation than the vertical transmission model would allow for.
 * Oblique transmission is cultural transmission being passed from one generation to another younger generation, such as is done by teaching, and the result of reproducing information across generations is a rapid loss of variation within that specific population. Unlike vertical transmission, oblique transmission doesn’t need to occur strictly between parent and offspring; it can occur between less-related generations (e.g. from grandparent to grandchild), or from an individual to a non-related younger individual of the same species.

Social Learning
Culture can be transmitted among animals through various methods, the most common of which include imitation, teaching, and language. Imitation is one of the most prevalent modes of cultural transmission in non-human animals, while teaching and language are much less widespread. In a study on food acquisition techniques in meerkats (Suricata suricatta), researchers found evidence that meerkats learned foraging tricks through imitation of conspecifics. The experimental setup consisted of an apparatus containing food with two possible methods that could be used to obtain the food. Naïve meerkats learned and used the method exhibited by the “demonstrator” meerkat trained in one of the two techniques. Although in this case, imitation is not the clear mechanism of learning given that the naïve meerkat could simply have been drawn to certain features of the apparatus from observing the “demonstrator” meerkat and from there discovered the technique on their own.

Teaching
In populations where social learning is lacking or costly, knowledgeable individuals of some species have been known to teach others. For this to occur, a teacher must change its behavior when interacting with a naïve individual and incur an initial cost from teaching, while an observer must acquire skills rapidly as a direct consequence. There is evidence for teaching in populations of ants (where a knowledgeable individual leads a naïve one to a food source through “tandem running”) and meerkats (where adults gradually teach pups scorpion-handling skills and monitor their performance). Hence, teaching is a direct way that local traditions can be passed down and transmitted.

Chimpanzees
In 1999, Whiten et al. examined data from 151 years of chimpanzee observation in an attempt to discover how much cultural variation existed between populations of the species. The synthesis of their studies consisted of two phases, in which they (1) created a comprehensive list of cultural variant behavior specific to certain populations of chimpanzees and (2) rated the behavior as either customary – occurring in all individuals within that population; habitual – not present in all individuals, but repeated in several individuals; present – neither customary or habitual but clearly identified; absent – instance of behavior not recorded and has no ecological explanation; ecological – absence of behavior can be attributed to ecological features or lack thereof in the environment, or of unknown origin. Their results were extensive: of the 65 categories of behavior studied, 39 (including grooming, tool usage and courtship behaviors) were found to be habitual in some communities but nonexistent in others.

Whiten et al. further made sure that these local traditions were not due to differences in ecology, and defined cultural behaviors as behaviors that are “transmitted repeatedly through social or observational learning to become a population-level characteristic”. Eight years later, after “conducting large-scale controlled social-diffusion experiments with captive groups,” Whiten et al. stated further that “alternative foraging techniques seeded in different groups of chimpanzees spread differentially…across two further groups with substantial fidelity”.

This finding confirms not only that nonhuman species can maintain unique cultural traditions; it also shows that they can pass these traditions on from one population to another. The Whiten articles are a tribute to the unique inventiveness of wild chimpanzees, and help prove that humans’ impressive capacity for culture and cultural transmission dates back to the now-extinct common ancestor we share with chimpanzees ..

Birds
In an experiment looking at vocal behavior in birds, researchers Marler & Tamura found evidence of song dialects in a species of sparrows. Located in the eastern and southern parts of North America, Zonotrichia leucophrys is a species of white-crowned song-birds that exhibit learned vocal behavior. Marler & Tamura found that while song variation existed between individual birds, each population of birds had a distinct song pattern that varied in accordance to geographical location. For this reason, Marler & Tamura called the patterns of each region a “dialect.”

By raising male sparrows in various types of acoustic settings and observing the effects of their verbal behavior, Marler & Tamura found that sparrows learned song “dialects” in about the first 100 days of life from older males. In this experimental setting, male birds in acoustic chambers were exposed to recorded sounds played through a loudspeaker. Using this setup in the laboratory, Marler & Tamura also saw that alien dialects could be taught, and that after learning the dialect, the sparrow’s verbal behavior were unaffected by the additional acoustic experiences, like the exposure of other dialects and songs from different species. It was also shown that white-crowned sparrows selectively learn songs of conspecifics. Marler & Tamura note that this case of cultural transmission is interesting in that it requires no social bond between the learner and the emitter of sound, given all emitted sounds originated from a loudspeaker in their experiments.

Dolphins
By using a “process of elimination” approach, researchers Krutzen et al. reported evidence of culturally transmitted tool use in bottlenose dolphins (Tursiops sp.). It has been previously noted that tool use in foraging, called “sponging” exists in this species. “Sponging” describes a behavior where a dolphin will break off a marine sponge, wear it over its rostrum, and use it to probe for fish. Using various genetic techniques, Krutzen et al. showed that the behavior of “sponging” is vertically transmitted from the mother, with most spongers being female. Additionally, they found high levels of genetic relatedness from spongers suggesting recent ancestry and the existence of a phenomenon researchers call a “sponging eve.”

In order to make a case for cultural transmission as the mode of behavioral inheritance in this case, Krutzen et al. needed to rule out possible genetic and ecological explanations. Krutzen et al. refer to data that indicate both spongers and nonspongers use the same habitat for foraging. Using mitochondrial DNA data, Krutzen et al. found a significant non-random association between the types of mitochondrial DNA pattern and sponging. Because mitochondrial DNA is inherited maternally, this result suggests sponging is passed from the mother.

In a later study one more possible explanation for the transmission of sponging was ruled out in favor of cultural transmission. Scientists from the same lab looked at the possibility that 1.) the tendency for “sponging” was due to a genetic difference in diving ability and 2.) that these genes were under selection. From a test of 29 spongers and 54 nonspongers, the results showed that that the coding mitochondrial genes were not a significant predictor of sponging behavior. Additionally, there was no evidence of selection in the investigated genes.

Matrilineal Whales
In the cases of three species of matrilineal whales, including pilot whales, sperm whales, and killer whales, mitochondrial DNA nucleotide diversities are about ten times lower than other species of whale. Whitehead found that this low mtDNA nucleotide diversity yet high diversity in matrilineal whale culture may be attributed to cultural transmission, since learned cultural traits have the ability to have the same effect as normal maternally inherited mtDNA. Indeed, the feeding specializations of these toothed whales are proposed to have lead to the divergence of the sympatric “resident” and “transient” forms of killer whales off Vancouver Island, in which resident killer whales feed on fish and squid, and transient whales feed on marine mammals. Interestingly, vocalizations have also been proven to be culturally acquired in killer and sperm whale populations, as evidenced by the distinct vocalization patterns maintained by members of these different species even in cases where more than one species may occupy one home range. Further study is being done in the matrilineal whales to uncover the cultural transmission mechanisms associated with other advanced techniques, such as migration strategies, new foraging techniques, and babysitting.

Black Rat
In the species of black rat (Rattus rattus), social transmission appears to be the mechanism of how optimal foraging techniques are transmitted. For this organism, the only source of food is pine seeds that they obtain from pine cones. Terkel et al. studied the way in which the rats obtained the seeds and the method that this strategy was transmitted to subsequent generations. Terkel et al. found that there was an optimal strategy for obtaining the seeds that minimized energy inputs and maximized outputs. Naïve rats that did not use this strategy could not learn it from trial and error or from watching experienced rats. Only young offspring could learn the technique. Additionally, from cross-fostering experiments where pups of naïve mothers were placed with experience mothers and vice versa, those pups placed with experienced mothers learned the technique while those with naïve mothers did not. This result suggests that this optimal foraging technique is socially rather than genetically transmitted.

Fish
Evidence for cultural transmission has also been shown in wild fish populations. Scientists Helfman and Schultz conducted translocation experiments with French grunts (Haemulon flavolineatum) where they took fish native to a specific schooling site and transported them to other sites. In this species of fish, the organism uses distinct, traditional migration routes to travel to schooling sites on coral reefs. These routes persisted past one generation and so by relocating the fish to different sites, Helfman and Schultz wanted to see if the new fish could relearn that sites’ migration route from the resident fish. Indeed this is what they found: that the newcomers quickly learned the traditional routes and schooling sites. But when residents were removed under similar situations, the new fish did not use the traditional route and instead use new routes, suggesting that the behavior could not be transmitted once the opportunity for learning was no longer there.

In a similar experiment looking at mating sites in blueheaded wrasse (Thalassoma bifasciatum), researcher Warner found that individuals chose mating sites based on social traditions and not based on the resource quality of the site. Warner found that although mating sites were maintained for four generations, when entire local populations were translocated elsewhere, new sites were used and maintained.

Controversies/Criticisms
A popular method of approaching the study of animal culture (and its transmission) is the “ethnographic method,” which argues that culture causes the geographical differences in the behavioral repertoires of large-brained mammals. However, this significantly downplays the roles that ecology and genetics play in influencing behavioral variation from population to population within a species. Behaviors stemming from genetic or environmental effects are not reliant on socially learned and transmitted information; therefore, they are not cultural.

Culture is just one source of adaptive behavior an organism exhibits to better exploit its environment. When behavioral variation reflects differential phenotypic plasticity, it is due more to ecological pressures than cultural ones. In other words, when an animal changes its behavior over its lifespan, this is most often a result of changes in its environment. Furthermore, animal behavior is also influenced by evolved predispositions, or genetics. It is very possible that “correlation between distance between sites and ‘cultural difference’ might reflect the well-established correlation between genetic and geographical distances”. The farther two populations of a species are separated from each other, the less genetic traits they will share in common, and this may be one source of variance in culture.

Another argument against the “ethnographic method” is that it is impossible to prove that there are absolutely no ecological or genetic factors in any behavior. Though culture has long been thought to arise and remain independent of genetics, the constraints on the propagation and innovation of cultural techniques inevitably caused by the genome of each respective animal species has led to the theory of gene-culture coevolution, which asserts that “cognitive, affective, and moral capacities” are the product of an evolutionary dynamic involving interactions between genes and culture over extended periods of time. The concept behind gene-culture coevolution is that, though culture plays a huge role in the progression of animal behavior over time, the genes of a particular species have the ability to affect the details of the corresponding culture and its ability to evolve within that species.

We do not know every possible genetic or environmental effect on behavior that exists, nor will we ever. In other words, it is impossible to reject the notion that genes and ecology influence all behaviors, to a degree. Culture can also contribute to differences in behavior, but like genes and environments, it carries different weight in different behaviors. As Laland and Janik explain, “to identify cultural variation, not only is it not sufficient to rule out the possibility that the variation in behavior constitutes unlearned responses to different selection pressures [from the environment], but it is also necessary to consider the possibility of genetic variation precipitating different patterns of learning.” Gene-culture coevolution, much like the interaction between cultural transmission and environment, both serve as modifiers to the original theories on cultural transmission and evolution that focused more on differences in the interactions between individuals.

Some scientists believe the study of animal culture should be approached in a different way. Currently, the question being asked is, “is this behavior learned socially (and hence is a result of culture alone), or is it a product of genes and/or environment?” However, it is impossible to find an absolute answer to this question, nor does one in all likelihood exist. Therefore it seems as though scientists should focus on examining how much variance in a behavior can be attributed to culture. Performing field experiments is an excellent way to try to answer this question: translocating individuals between populations or populations between sites could help biologists distinguish between culture, ecology and genetics. For example, if a newly introduced animal shifts its behavior to mimic that of others in its new population, genetic difference as an effect on behavior can be ruled out.

Unanswered Questions/Future Areas of Exploration
In the study of social transmissions, one of the important unanswered questions is an explanation of how and why maladaptive social traditions are maintained. For example, in one study on social transmission in guppies (Poecilia reticulata), naive fish preferred taking a long, energetically costly route to a feeder that they had learned from resident fish rather than take a shorter route. These fish were also slower to learn the new, quicker route compared to naïve fish that had not been trained in the long route. In this case not only is the social tradition maladaptive, but it also inhibits the acquisition of adaptive behavior.