"Behaviour Genetics: A Critical Perspective on the

Behaviour Genetics: A Critical Perspective on the Role of Genes in Behaviour Timo Järvilehto, Robert Lickliter,

Advanced article Article Contents • Introduction • Methodological Problems in Behavioural Genetics • Genes or Environment as Explanation of Behaviour? • Determination of Genetic Risks • Related Articles

University of Oulu, Oulu, Finland Florida International University, Miami, Florida, USA

Online posting date: 16th August 2016

Based in part on the previous versions of this eLS article ‘Behaviour: Role of Genes’ (2006, 2009).

Much effort in behavioural genetics has been motivated by the hope that one day aspects of human behaviour will be explicable in genetic terms. This hope is based on the assumption that the contribution of genetic and environmental factors to behaviour can somehow be partitioned. However, recent advances in genomics, epigenetics, cellular and developmental biology and developmental psychology have made it clear that such partitioning is biologically implausible. The functional signiﬁcance of genes or any other inﬂuence on phenotypic development can be understood only in relation to the organism–environment system of which they are a part. Genes and environments are neither alternative nor independent causes for behavioural development.

Introduction Reports and press releases can be encountered regularly declaring the ‘first demonstration’ of the relation between a gene and a specific form of human behaviour, its disturbance/disease or a given personality trait. Dyslexia, intelligence, schizophrenia, attention disorders, aggression, homosexuality, criminality, novelty seeking, extroversion and obesity have all been reported to have a relation to the action of specific genes (Comuzzie and Allison, 1998; McGuffin et al., 2001; Ebstein, 2006). Most researchers agree, of course, that both genes and environment are involved in shaping human behaviour, or that all human traits are based on some kind of interaction between genetic and environmental factors. eLS subject area: Bioethics & Philosophy How to cite: Järvilehto, Timo and Lickliter, Robert (August 2016) Behaviour Genetics: A Critical Perspective on the Role of Genes in Behaviour. In: eLS. John Wiley & Sons, Ltd: Chichester. DOI: 10.1002/9780470015902.a0006181.pub3

Behavioural genetics is a multidisciplinary field of research studying the role of genetic influences as possible contributors to individual differences, human behavioural traits and behavioural disturbances and diseases. One of the motives of this research area is to develop methods for controlling human behaviour (gene technology) and its disturbances (gene therapy). Research in behavioural genetics is based on the conviction that the relative proportions of genetic and environmental influences can be determined, and that this knowledge may be applied to understanding and improving human behavioural characteristics. Inherent in these convictions is the assumption that genes and environment can make independent contributions to behavioural development. However, the basic assumptions of behavioural genetics have evoked strong criticism and doubts as to their scientific validity (Allen, 1998; Gottlieb, 2006; Lewontin, 2001; Lickliter and Honeycutt, 2015; Moore, 2013; Rose, 1997). It has been somewhat surprising to find that the number of human genes (now estimated at about 22 000) does not differ considerably from that of dramatically different species such as worms or fruit flies. Furthermore, the difference between the genomes of African great apes and humans is only about 1%, and all humans share about 99.9% of their genome. It is also known that genes vary more within human races than between them. It is difficult to understand how such small differences in genetic material could lead to differences in phenotype and behavioural capabilities. One suggestion has been the presence of single nucleotide polymorphisms (SNPs) that vary considerably between individuals and have been assumed to be the basis of the diversity of human variation.

Methodological Problems in Behavioural Genetics A great leap forward was made in genetics when the first drafts of the human genome were achieved. It was widely believed that this achievement would revolutionise psychology and psychiatry and open the door for gene technology in humans. However, although the financial support for the human genome project was unprecedented, not all researchers agreed that such a goal

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Behaviour Genetics: A Critical Perspective on the Role of Genes in Behaviour

could be attained, even in principle. The doubts were not so much directed at the scientific foundation of quantitative genetics, which has shown remarkable success in delineating genetic components of complex traits in plants and animals, but rather at the problem of whether its methods can be properly applied to the study of the genetic basis of human behaviour.

Methods Research in behavioural genetics involves two basic assumptions: (1) with a combination of genetic and behavioural methods, the contribution of genetic and environmental factors to human behavioural traits may be intelligibly partitioned and (2) it is possible to identify genes that determine specific phenotypic traits and behavioural disturbances/diseases. When studying the relation between genes and human behaviour, the standard research procedure starts with the definition of a behavioural trait. This is usually based on established diagnoses or on the use of psychological tests and questionnaires. The next step is the study of the occurrence of the defined behavioural trait in a family, pedigree, twins or adopted children in varying environments. On this basis, the heritability of the studied trait may be determined. This kind of study does not help in locating genetic factors in an individual; the heritability estimate shows only that a certain amount of the variance of the studied trait in a population may be ascribed to inherited factors (Moore, 2013). The ‘heritability’ of a trait tells us about a population that has been studied, but not about the development of the trait itself. New technology using chromosomal markers has made it possible to search for individual genes or predisposing genetic factors (quantitative trait loci, QTL) that may contribute to a particular trait in a studied population. The occurrence of the genetic marker may be correlated with the studied trait in families or pedigrees. Markers are any detectable elements in chromosomes or in deoxyribonucleic acid (DNA) that can be followed in a pedigree and correlated with the presence or absence of the studied phenotype. Although biochemical genetic methods are highly developed and allow chemical analysis of the human genome with great accuracy and speed, there are several methodological problems that have not yet been adequately resolved. These problems are related mainly to the complexity of genes themselves, to the behavioural methods used and to the interpretation of the genetic correlates of behavioural traits or disturbances.

Complexity of genes Modern biotechnology allows rapid and exact determination of gene sequences, which facilitates the determination of genetic correlates of behavioural variables to an extent not possible even a few decades ago. Thus, it is generally believed that it will take only a short time until we know all of the behavioural functions attributable to genes. There are several problems on the genetic side, however, which make the interpretation of correlations difficult. There are at least four such characteristics of genes: (1) a single gene may participate in the production of several proteins; (2) different genes may have overlapping functions; (3) there may be interactions between different genes, that is, the presence of the product of one gene may be important for another gene to 2

have any function at all; and (4) the expression of a gene in a cell depends on intracellular and extracellular factors, many of which are still unknown. A hormone, for example, may turn a gene on or off, or influence the degree of its expression (Crews, 2008).

Problems of behavioural measurements Another aspect of the methodological problems associated with behaviour genetics consists of the determination of the behavioural variables correlated with the presence or absence of a certain allele of a given gene. Several groups of behavioural phenomena have been studied, including (1) behavioural disturbances and diseases (attention disorders, autism, Parkinsonism, Alzheimer disease, alcoholism, schizophrenia, bipolar illness), (2) behavioural traits (intelligence, learning, memory), (3) personality traits (extroversion–introversion, anxiety, novelty seeking) and (4) traits related to social attitudes (antisociality, criminality, homosexuality). The main scientific criticism of behavioural genetics may be directed precisely at the way behavioural methods are used. Epigenetic developmental pathways linking genes to behaviour are extremely complex and difficult to study, not only because of the biochemical complexity but also because of difficulties in the quantification of behaviour. The problems with behavioural methods are related to the fact that behavioural traits or disturbances are often poorly defined. It is more than usual that the studies reported rest on no comprehensive theory of behaviour, or if a theory is mentioned, it is not adequately specified. Furthermore, medical diagnoses and results of psychological tests are often accepted without taking into account that such methods do not necessarily allow selection of homogenous samples for the study. There is a big difference between linking genes and specific diseases, and getting similar information with respect to complex disorders or behavioural traits. Although diseases are usually better defined than behavioural disturbances, one has to bear in mind that the concept of disease combines a very heterogeneous group of qualitatively different phenomena that may range from lack of a specific biochemical compound to disorders with unknown etiology. It is true of course that many diseases are relatively unequivocal, in the sense that it is possible to show a single factor that seems to be central in the development of a given disease. In haemophilia, for example, it can be shown that the disruption of the function of a gene is responsible for a deficiency in the production of protein necessary for coagulation of the blood. Parkinsonism, influenza and schizophrenia are also such diseases, although quite different aetiological factors and behavioural phenomena are involved in each case. In fact, a disease may be based on any structural or functional difference that prevents the normal action of an individual, hampers his life processes or makes interactions with other people difficult. Thus, a disease is not an entity that has crept into the human body with the help of ‘bad’ genes, for example, but reflects a relation between problematic bodily changes and some functional criterion or norm. The functional ability of an affected individual does not correspond to our expectations of people. Thus, every definition of a disease is eventually a social one.



Similarly, most behavioural traits/disturbances and psychological measures are based on comparisons among people. Tallness, for example, may be measured in centimetres, but someone is considered tall only if some other people are shorter. Thus, tallness as a property of an individual is not located in the individual, but exists in relation to other individuals. Properties that are not located in an individual cannot be transferred from one individual to another by means of genes. Genes offer structural possibilities, but the properties and behavioural traits of individuals are created by interactions between an individual and his/her world. Although genes certainly have a role in determining how well one’s height correlates with the height of one’s parents, it is problematic to conclude that this tallness is genetically determined. Finally, a critical feature in all genetic studies is control of environmental variation. In animal and plant studies, such control may be carried out in an exact manner and without considerable ethical problems. In studies with humans, however, the definition and control of environmental factors is extremely difficult. Physical, biological, social and cultural factors are important in the formation of human behavioural characteristics and traits; however, a rigorous definition and assessment of these environments is problematic. In this respect, many studies in behavioural genetics would never pass the threshold for publication in journals of agronomy or animal breeding (Lewontin, 2001).

Genes or Environment as Explanation of Behaviour? Most scientists agree that both genes and environment influence human behaviour; the main source of disagreement is the role of these factors in explaining it. Can specific genes or polymorphic regions in the chromosomes explain different forms of human behaviour, behavioural traits or psychological abilities, and to what extent are environmental factors involved. Are quantitative estimates of genetic and environmental factors possible in respect to these phenotypic outcomes?

Partitioning of genetic and environmental effects The starting point of many behavioural genetic studies is the estimation of heritability, which directs the research to certain chromosomes and to their specific polymorphic regions. However, estimates of heritability do not tell anything about the specific roles of genes, as genes are not the only inherited factors involved in development. In addition to genes, a fertilised egg also contains the various cell structures that make the development of an individual and his/her behavioural outcomes possible. Genes are one of many contributors to a complex network of interactions, including molecular, cellular, hormonal and environmental components (Johnston and Edwards, 2002). Thus, the function of a gene cannot be separated from the multiple contexts and environments in which it functions. The idea of genes and environment as two separate factors implies that an organism (with its genes) and its environment can exist separately. However, this assumption is clearly wrong

(Lewontin, 2001; Rose, 1997; Järvilehto, 2000). An organism and its environment belong together; they are always fundamentally connected. No organism develops or survives without an environment, and no environment without an organism is possible, because an environment is by definition that which environs an organism. However, even if the organism and environment belong together, is it possible to partition the effects of genes and environment on the behaviour of an organism? But what is the ‘environment’ that is contrasted with genes? A gene is a chemical compound that may act as a gene only as a part of an organism. Together with its chemical environment, it regulates the formation of proteins, which also have their own environment (other proteins and structural elements), that make up the cell. The cell connects to its specific metabolic environment and to other cells in the development of a multicellular organism. Signals from the intracellular and extracellular environment of a gene, including hormones, neurotransmitters, nutrients and social interaction, regulate gene activity (Moore, 2015). This constellation also has its specific environment, which makes behaviour possible only as a process in an organism–environment system (Järvilehto, 2000). An organism and its behavioural environment cannot be functionally separated, because any behavioural result presupposes the existence of elements that belong to the organism as well as to its environment. It is precisely the behavioural environment with which genes are usually contrasted in behavioural genetics. However, such a contrast does not make sense, because the genes belong themselves to the same system as the environmental factors. Thus, genes are involved in all behaviour. Behaviour without genes is as impossible as is behaviour without an environment. The only ‘environment’ that could be contrasted with genes is their specific chemical environment, but this would be nonsense, because it is just this environment that makes the action of genes possible (Johnston and Edwards, 2002).

Behaviour as integration of organism and environment The behaviour of an organism entails all relevant parts of the organism and environment that are necessary to the achievement of behavioural results. Thus, genes and all qualitatively different environments (physical, biological, social) are constituents of one and the same system, the organism–environment system, and there is no reason to think that only one part of the system could determine or control its organisation, its processes or the properties of the system (Gottlieb et al., 2006). Furthermore, as genes participate as one factor in the formation of the structures of an organism, they also contribute to the selection of the environmental parts of the behavioural environment. Not even in this sense can genes and environment be regarded as independent components. The contrast between genes and environment is based on the conception that a researcher may measure the environments of studied individuals or vary them systematically. However, the definition of significant environmental characteristics is extremely difficult, if not impossible. Every organism–environment system contains environmental parts that make up its behavioural environment according to its own intrinsic structure and in relation to the expected behavioural results


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(Järvilehto, 2000). Even in physically similar environments that may be controlled by a researcher, the behavioural environments may differ because of ascription of different meanings to seemingly similar environmental elements. Thus, it is possible, for example, that identical twins sharing the same family have qualitatively more different environments than do twins fostered in different families. There is no possibility for objective control of the behavioural environments. If the environment cannot be precisely controlled, there is no adequate way of determining the relative influence of genes and environment. Attempts to sort out how much genes, as opposed to environment, shape human behaviour may therefore be a scientifically meaningless activity. Studies in behavioural genetics do not typically recognise this problem, and ‘environment’ is simply defined on the basis of the operations of the researcher. As genes comprise only a part of the organism–environment system, their role in explaining normal behaviour of the whole system cannot be isolated. It is clear, of course, that a mutation or a missing gene at a critical place in a system may have dramatic effects on behaviour, similarly to the way a piece of trash in the carburettor of a car may stop the car. However, in addition to genes, many other factors contribute to the characteristics of behaviour. Even if we could determine all genetic and environmental parts of a system, we could not estimate their contribution, because they are all needed for the appearance of a given trait. Genes, in and of themselves, cannot produce any behavioural outcome, because gene–environment co-action is a necessary requirement of normal as well as abnormal development (Gottlieb, 2006). If we consider that a trait is the result of a relation between factors, we see that it is simply impossible to ascribe a causal role to a single gene, set of genes or even to the whole genome. Every human being is born with all inherited structures into an environment, which is also partly inherited, but not ‘ready’; rather, it offers different ways to achieve behavioural results, which in turn change the behavioural possibilities, personal properties and expression of his/her genes. Thus, controlled manipulation of human properties (e.g. increasing intelligence or abolishing behavioural disturbances) by manipulating only parts of the genome is not possible, and has no scientifically tenable basis.

Determination of Genetic Risks All the considerations above also apply in relation to the prognostic use of genetic tests. It is generally believed that genetic testing will help in determining the risk of developing diseases or behavioural disturbances. However, as every disease or behavioural capability is the result of the integrated co-action of genes and environmental factors, there is no possibility of estimating the risk of getting a given disease only on the basis of genetic factors. A ‘disease risk’ based on individual genetic tests is at best only a statistical measure, the application of which to a given individual may be misleading. Furthermore, although anticipative diagnoses may be useful, they may be also dangerous, because – in addition to the possibility of mistakes – there is the danger that the diagnosis and the resulting fear of having a certain disease may promote the prevalence of this disease, 4

independent of possible changes in the way of life aimed at its prevention. Thus, the determinations of ‘risks’ may turn out to be self-fulfilling prophecies (Sternberg and Grigorenko, 1999).

Related Articles Animal Models of Human Behaviour Gene-Environment Interaction Genetic Isolates and Behavioral Gene Searches Gene-to-behavior Pathways Williams Syndrome: A Neurogenetic Model of Human Behavior

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McGuffin P, Riley B and Plomin R (2001) Genomics and behavior: toward behavioral genomics. Science 291: 1232–1249. http://www3.interscience.wiley.com/cgi-bin/reflink?object= TYPE%3DJCIT%26BIBID%3DBIB6%26SNM%3DMcGuffin% 26SNM%3DRiley%26SNM%3DPlomin%26JTL%3DScience% 26PYR%3D2001%26VID%3D291%26PPF%3D1232 &&ENABLECAS=Y. Moore DS (2013) Behavioral genetics, genetics, and epigenetics. In: Zelazo PD (ed.) Oxford Handbook of Developmental Psychology, Vol 1: Body and Mind. New York: Oxford University Press. Moore DS (2015) The Developing Genome: An Introduction to Behavioral Epigenetics. New York: Oxford University Press. Rose SPR (1997) Lifelines: Biology Beyond Determinism. New York: Oxford University Press. Sternberg RJ and Grigorenko EL (1999) Myths in psychology and education regarding the gene–environment debate. Teachers College Record 100: 536–553. http://www3. interscience.wiley.com/cgi-bin/reflink?object=TYPE%3DJCIT% 26BIBID%3DBIB8%26SNM%3DSternberg%26SNM% 3DGrigorenko%26JTL%3DTeachers+College+Record%26PYR% 3D1999%26VID%3D100%26PPF%3D536&&ENABLECAS=Y.

Further Reading Ehrlich PR (2000) Human Natures: Genes, Cultures, and the Human Prospect. Washington DC: Island Press. Gottlieb G (1997) Synthesizing Nature/Nurture. Mahwah, NJ: Erlbaum. Lewontin R (2000) It Ain’t Necessarily So: The Dream of the Human Genome and Other Illusions. New York: New York Review of Books. Lickliter R and Honeycutt H (2003) Developmental dynamics: towards a biologically plausible evolutionary psychology. Psychological Bulletin 129: 819–835. Moore DS (2002) The Dependent Gene: The Fallacy of “Nature vs. Nurture”. New York: Freeman.


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