Domesticated Animals

Over thousands of years, humans have domesticated animals for various reasons. Among these domesticated species companion animals hold multiple questions, from why do humans have companion animals to how certain desired behavioral traits developed. When observing closely related species or species with a common ancestor one can clearly see the difference along with similarities among a variety of traits. Behavior, just like any other trait, can also be observed and related to closely related species or species with common ancestors. The main focus of this research is to understand these similarities and differences among closely related species or species with a common ancestor at a genetic level. The connection between genetics and behavior

has been controversial in the scientific community for as long as scientists have tried to explain behavior, traits, genetics and other observations in the animal kingdom. A link between the two has been dismissed and rediscovered again and again.
First, we must understand how traits are passed on from parent to offspring. Let's think of it in terms of parents (mother and father) teaching their child how to bake a cake by following a specific recipe. Each parent brings certain ingredients to the prepping station, these ingredients in genetics is the genetic code. Let's say the mother only brought some of the ingredients that she found in the fridge and the father only brought some of the ingredients that he found in the cabinet. We can compare the fridge and cabinet with each parent’s gametes, which in males is sperm and in females eggs. Therefore each parent is contributing different genetic code that will, due to fertilization (combination of sperm and egg), be passed on to the offspring. The next step would be to measure out how much of each ingredient is necessary for the recipe. Genetically we can think of this as the formation of an allele. Alleles can be either dominant or recessive: you will have some ingredients that will influence the taste every time you use it, like cocoa, this will be the dominant allele. Whereas other ingredients will only be tasted if they are added in by themselves, like vanilla, this will be the recessive allele. Because the offspring receives a gamete from each parent, each parent contributes an allele to form a gene, this can be seen as the mixing of the ingredients. This combination, however, can be heterozygous or homozygous. A homozygous gene is when both parents add a dominant allele or when both parents add a recessive allele. Therefore if both parents add cocoa the cake will be chocolate flavored (dominant alleles passed on) or if both parents add vanilla the cake will be vanilla flavored (recessive alleles passed on). However a heterozygous gene is when one parent adds a dominant allele and the other parent adds a recessive allele, in this form the dominant allele will be expressed. Therefore if one parent adds cocoa and the other parent adds vanilla the cake will be chocolate flavored because the cocoa has a more dominant flavor than the vanilla. Now we are left with the batter for the cake, the offspring now has the genotype for the specific trait. The genotype is all the genetic code needed for a specific trait or in other words all the ingredients for a specific type of cake. The final cake that comes out of the oven is the phenotype or the trait that can be observed, like behavior. This process of the parents teaching the child how to bake a cake can be seen genetically as inheritance of a trait. If a trait is heritable you can select for it in the breeding process.
It is reasonable to expect that some of the behavioral differences among people are genetic in origin. Not all differences in behavior are due to genetics, behavioral genetic research demonstrates that environmental influences are also important. Genes are chemical structures that can only code for amino acid sequences. These amino acid sequences interact with all of what we are and can thus indirectly affect endpoint so as complex as behavior, but there is no gene for a particular behavior. All effects of genes on behavioral variability are indirect, representing the cumulative effects of stretches of amino acids that differ from person to person and that interact with the intracellular and extracellular environment. However, there are no known single genes that account for a significant portion of individual differences for any complex behavior. This is not surprising, considering the complexity of behavior. Molecular genetic research with organisms as simple as bacteria makes it clear that many genes affect even the simplest behaviors. Greater complexity is added by the fact that any single gene can affect many behaviors. The technical words for these two concepts are polygyny and pleiotropy. Polygyny means that normal behavioral variation is influenced by many genes, each of which contributes small portions of variability to the behavioral differences among individuals. Pleiotropy refers to the multiple, indirect effects of genes on behavior. In other words, polygyny and Pleistocene mean that one gene can affect many behaviors. Therefore, any one of many genes can disrupt development, but the normal range of behavioral variation is likely to be orchestrated by a system of many genes, each with small effect, as well as by environmental influences. In addition to polygyny and pleiotropy, a third factor that plays a role is population. Genetic influence on behavior refers to the association between genetic differences and behavioral differences among individuals in a particular population. These estimates of genetic influence are not constants like the speed of light; they are statistics that describe a particular population. Change the population - genetically or environmentally - and you change the result.
In the late 1700s and the beginning of the 1800s a scientist by the name of Jean Baptiste Lamarck came up with an evolutionary theory about the inheritance of behavior. Lamarckian inheritance stated that acquired traits can be inherited from parent to offspring. In other words Lamarck said that for example if the parent goes to the gym and gets bigger muscles that the bigger muscles will be inherited by the offspring. This theory was never really accepted and with today’s knowledge of heritability and genetics it is completely dismissed. Even though this theory is dismissed Lamarck was on the right track in terms of some part of the acquired trait being heritable, especially with behavior. For example when is an animal no longer considered a tamed wild animal but a domesticated animal? Tameness is an acquired trait learned in the animal’s lifetime, therefore according to the dismissal of Lamarckian theory not inheritable. Whereas domesticated animals are born domesticated, not needing to learn the trait of domestication throughout their lives, therefore making it a trait that can be inherited.
In both the U.S. and Australia, 63% of households include pets. In the U.S. the proportion of households with pets is larger than those with children. Today this is manifested in the adoption of animals and the care provided to them in the course of that relationship. The roots of this relationship may be founded in the development of three recognized traits of humans: making and using tools, symbolic behavior, and the domestication of other species. It is also believed that animal connection is a fourth trait, tying the other three together. Therefore animal connection has an immense effect on human evolution, genetics and behavior. Domestication required humans to select for desirable behavioral traits and controlling reproduction along with genetic output over multiple generations. Humans therefore, had to live in close proximity to animals, historically even bringing them into their home. Even though this closeness has allowed some infectious diseases to enter the human population from the original animal hosts, for example measles from dogs, mumps from poultry, tuberculosis from cattle and the common cold from horses. The benefits have outweighed the costs when it comes to keeping animals near and over time animals have become much more that just a food source.
Although a lot of exposure occurred of the monkey that appears to have adopted a cat, such cross-species alloparenting is rare with the exception of humans. Animals were domesticated as living tools which expanded the reach of humans making other resources more accessible. Most domesticated animals originated as farm animals with the exceptions of cats and dogs. Animal could provide labor, milk, wool as well as opportunity for the production of tools and clothing. Furthermore animals have contributed to an understanding of biology, ecology, physiology, temperament and intelligence.
Wolf domestication began approximately 11,000 years ago from the Canis lupus family. Wolf domestication originated as a result of natural selection and genetic drift that later blended into artificial selections by humans. This “cultural” process is believed to have gone something like this: a pack of “less afraid” wolves approached an early human camp to scavenge for food. Over time the interactions between wolf and early human became more resulting in the first utility for domesticated wolves - guards to the camp. With more artificial selection humans bred for desired traits and other utilities such as hunting with humans came about. Even though dogs have been domesticated for thousands of years, the wide phenotypic variation is very recent resulting in 400 recognized breeds by the Dog Breeders Association.On the other hand wild cat domestication happened many years later, about 7,000 years ago. The first domesticated wildcats originated by natural selection and it is sought to be due to cats exploiting humans for shelter and other resources. Cats have very little to no utility in comparison with dogs. Domestication of cats started as a self selective process due to a small population being isolated within a human community. Therefore correlating character with habitat of choice.
Domesticated species are not necessarily a separate species from their wild ancestor, due to the fact that they are interfertile and can intercross given the opportunity.

Now let's think about when an animal is truly considered domesticated. There is no concrete definition for domestication due to the fact that domestication is a continuous transition, attributes differ by species as well as genes and environment that interact to produce selectable characters that may vary with circumstance. However there is an interconnective and characteristic suite of modifiable traits involving physiology, morphology and behavior that is often associated with domesticated animals. Critically all domesticated animals manifest a remarkable tolerance of proximity to, or even an outright lack of fear for humans. Domestication behaviorally is not a single trait but a suite of traits so praising elements affecting: mood, emotion, agonistic and affiliative behavior, and social communication that is all modified in some way. It is important to understand the distinction between taming and domestication. Taming is conditioned behavioral modifications of an individual, whereas domestication is permanent genetic modification of a bred lineage that leads to, among other, a heritable predisposition toward human association. Trade marks of tameness is a decrease in flight behavior and in increase in social

behavior.
Differences among breeds in domesticated animals provide unique opportunity for studying the genetics of behavior, morphology and complex disease.

New technology, techniques and tools also make it easier to study the genetics of behavior, morphology and complex disease in domesticated animals that could easily be related to humans. Some of these tools include readily available information on gnomes, not only for different species but for different breeds within a species. Some technique using the genomes involves looking at the entire genome and locating the “causative” haplotype block, followed by fine-mapping focusing on a specific region across different breeds, therefore providing a better knowledge on the genotypic information. The next step would be to measure and classify behaviors such as herding, pointing and that “indefinable character” so treasured by

humans.
Domestication as a specific form of evolution offers valuable insight into how genomic variation contributes to complex differences in phenotypes, including both morphological and behavioral traits. Behavioral changes associated with the domestication of animals offer one of the most compelling demonstrations of influences that genes have on behavior. Overall the behavior of domesticated species differed dramatically from wild counterparts, and because these “tame” behavioral phenotypes “breed true” in all domesticated animals. Therefore, domestication clearly represents an evolutionary process involving the genotypic adaptation of animals to the captive environment. Domesticated animals share some common traits: changes in body size, changes in fur coloration, changes in the timing of the reproductive cycle, hair or fur becomes curly, floppy ears, shortened or curly tails.
One study, in particular, opened many doors for studying genetic behavior, and that is Dmitri K. Belyaev, a Russian scientist at the Institute of Cytology and Genetics of the Russian Academy of Sciences in Novosibirsk Russia, that studied the domestication of the red fox, turned silver fox in 1959. The rapid success of Belyaev’s silver fox experiment was truly outstanding. His “tame” and “aggressive” strains were developed in a blink of an eye on an evolutionary scale, and breed true to this day.The red fox (Vulpes vulpes) and other fox-like and dog-like carnivores that form the Canidae family, diverged from a common ancestor some 10-12 million years ago. The silver fox is a naturally occurring melanistic variant of the red fox. Because comparative cytogenetic, molecular genetic, and phylogenetic analyses have clarified evolution divergence, and conserved homologies of these candies genomic tools developed in one such species can be applied to address questions in other members of the family. Belyaev wondered if selecting for tameness and against aggression would result in hormonal and neurochemical changes, considering behavior ultimately emerged from biology. Those hormonal and chemical changes could then be implicated in anatomy and physiology. It could be that anatomical differences in domesticated dogs were related to genetic changes underlying the behavioral temperament for which they selected (tameness and low aggression). Belyaev and his colleagues took wild silver foxes, the naturally occurring variant of red foxes, and bred them with strong selection criteria for inherent tameness. By one month postnatal the foxes became eager to interact with humans, whimpering to attract attention and then sniffing and licking humans like puppies.
The first physiological change observed was in the hypothalamic-pituitary-adrenal axis. This system controls adrenaline, which is a hormone produced in response to stress, and also controls fear-related responses. The silver fox adrenaline levels significantly decreased resulting in the selected inherent tameness. Secondly, it was hypothesized that adrenaline might share a biochemical pathway with melanin, which controls pigment produced in fur. As a result selecting for a single behavioral characteristic - allowing only tameness, least fearful individuals to breed - resulted in changes not only in behavior but also in anatomical and physiological changes that were not directly manipulated. Tame foxes, unlike their aggressive counters train, and dogs, unlike wolves, have evolved social cognitive mechanisms that more closely resemble human social cognitive skills than do those of chimpanzees, enabling them to interact with humans. Critically, these tame foxes were not directly selected for such social skills but for reduced fear-based aggression towards humans; the social communicative skills subsequently emerged spontaneously. Their behavior was highly social toward humans and members of their own species, in a playful and friendly manner.This supports the emotional relativity hypothesis, I.e., that evolution of human-like temperament (social tolerance) was the necessary prerequisite for significant social cognitive evolution in humans, dogs, and now foxes. To ensure that the tameness was a result of genetic inheritance, foxes were not trained and were only allowed brief “time dosage” contacts with humans. Belyaev also bred for the opposite, aggressive behavior to see what the outcome will be. The tame and aggressive fox strains differ in many districts and specific behavioral traits: their position and posture within their cage when approached by humans, notices that they made, carriage of their ears and tail, willingness and desire to be touched as opposed to eagerness to attack and bite. Morphologically they were also different with a darker fur color, almost black, pointier ears and much larger in size.
Silver fox experiment provides a rich resource for investigating the genetics of behavior, with Strauss developed by intensely selective breeding that display markedly different behavioral phenotypes. This effort resulted in the newest addition to the range of truly domesticated species, and a unique opportunity to examine molecular determinants of behavioral changes that occur during domestication. In particular, one expectation of the silver fox experiment is that it will be synergistic with studies in other species, including humans, to yield a more comprehensive understanding of molecular mechanisms and evolution of a wider range of social cognitive behaviors. The combination of opportunities for genetic mapping of behavioral loci in experimental informative pedigrees, selection sweep identification in populations under intense selection, and comparative expression analysis for identification of loci and genes for behavior makes the silver fox experiment a powerful model, intermediate between rodents and primates in biological complexity, for gaining insight into genetics of social behaviors. It is important to remember when attempting to understand behavior, a guiding principle is that behavior is complex. Furthermore, even as certain aspects of behavior yield to various analyzes, there still remains unresolved complexity.
In the domain of cognitive abilities, controversy abounds concerning the validity and the value of IQ test scores. Nonetheless, IQ tests are the most widely used measures of intelligence and also predict education and income better than any other behavioral attribute of individuals. Data from multiple studies make it difficult to escape the conclusion that heredity significantly influences individual differences in IQ scores. We can go beyond this issue to ask about the magnitude of the effect. How much does heredity affect IQ scores? The data suggests that genetic differences among individuals account for about half of the differences in individuals’ performance on IQ tests. If half of the variance of IQ scores is due to heredity, the other half is due to environment. Much of the environmental variance appears to be of the type shared by family members. As a result, if about 50% of the variances for IQ scores is genetic in origin, and if about 30% of the variance is due to shared environment, the rest of the variance is due to non-shared environment (about 10%) and error of measurement (about 10%).
Understanding how genetics shape behavior is also important in psychopathology for understanding complex mental disorders and developing treatments. Two major types of psychosis, severe mental illness, that is most researched is schizophrenia and affective disorders. Schizophrenia is characterized by long term thought disorder, hallucinations and disorganized speech. Affective disorders can be further categorized into depression, unipolar depression, and depression alternating with manic mood swings, bipolar depression. Most twin studies on schizophrenia indicate that the familial resemblance is due to heredity rather than shared environment. Furthermore, this study indicates that genetic influence exceeds that of most common medical conditions such as diabetes, ulcers, chronic obstructive pulmonary disease, hypertension and ischemic heart disease. This proves how important understanding genetic links to behavior truly is. Depression is the most common mental disorder, marked by feelings of sadness, disturbances of sleep and appetite, loss of energy and suicidal. Manic depression on the other hand is hyperactivity, reduced need for sleep and euphoria. The difficulty of diagnosing this disorder creates ambiguity in ascertaining base rates in the population making studies incredibly difficult. This resulted in contradicting conclusions from studies and these differences in twin and adoption study data suggest caution in reaching conclusions about the relative importance of genetic and environmental factors. Since this is the most common mental disorder it is clear more research needs to be done in order to obtain more concrete results.
Another mental disorder that has recently gained a lot of attention in the media for its genetic linkage is alcoholism. Alcoholism in a first degree relative is by far the single best predictor of alcoholism. Studies has shown that 25% male relatives of alcoholics are themselves alcoholics compared with less than 5% of males in the general population. Twin and adoption studies have found evidence for genetic influence on quantity of alcohol consumed among normal drinkers. This data suggests very substantial genetic influence and only slight influence by shared environment. Alcohol use and abuse is a good example of how genetics influence behavior, however no matter how strong hereditary propensity toward alcoholism might be for males, no one will become alcoholic unless large quantities of alcohol are consumed over a long period of time. It is highly unlikely that genes drive people to drink. What is more likely to be inherited is an absence of “brakes”- physiological and psychological factors that make most people want to stop drinking after a certain point of intoxication. Finding the subtype of alcoholism increases the likelihood that interventions will be found to prevent alcoholism before it irrevocably devastates lives of affected individuals, as it is, a tenth of advanced alcoholics successfully recover.
Recent research shows that heredity can affect environmental measures and that heredity can also mediate associations between measures of environment and behavioral outcomes. This is an important finding because it means that some supposedly environmental factors that influence development are in fact genetic factors. This does not say that finding genetic effects on environmental measures necessarily disqualifies attempts to intervene. As is the case for all behavioral genetic factors analyses heritability only indicates that genetic factors are important given the current range of genetic and environmental influences. As behavioral neuroscience advances in the post- genomic era, it becomes increasingly incumbent on investigators from diverse disciplines using divergent methodologies to work together in a reciprocal and mutually informative fashion in the pursuit of knowledge.
Genetic influence is important for many aspects of behavior, including cognitive abilities, personality, and psychopathology. Even within these major domains, the possibility for applications of behavioral genetics is abundant. More areas to be researched for example, include vulnerability and invulnerability to stress, emotional regulation, interest and abilities, social cognition, familial and no familial relationships, life satisfaction and so much more. By researching the domestication of animals important insights into the world of behavioral genetics become possible and these insights can be translated to humans. It could be argued that the more is known about a trait genetically as well as environmentally, the more likely it is that rational intervention and prevention strategies can be devised. For now we can conclude that nature and nurture is important in animal development.