Behaviour: Role of Genes Timo Ja ¨rvilehto, University of Oulu, Oulu, Finland Robert Lickliter, Florida International University, Miami, USA Based in part on the previous version of this Encyclopedia of Life Sciences (ELS) article, Behavior: Role of Genes by Timo Ja ¨rvilehto. Much effort in behavioural genetics has been motivated by the hope that one day 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, 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 phenotypic traits. Introduction Reports and press releases may be encountered almost daily declaring the ‘first demonstration’ of the relation be- tween a gene and a specific form of human behaviour, its disturbance/disease or a personality trait. Dyslexia, intel- ligence, schizophrenia, attention disorders, aggression, homosexuality, criminality, novelty seeking, extroversion and obesity have 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 shape human behaviour, or that all human traits are based on some kind of interaction between genetic and environmen- tal effects. However, it is widely believed that the explana- tion for many forms of human behaviour and its disturbances will be provided by the characteristics of the human genome. Sometimes an impression is given that the knowledge of the genome is sufficient even for computing the human organism with all its behavioural capabilities. Behavioural genetics is a multidisciplinary field of re- search 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 is the opportunity to develop methods for controlling human behaviour and its distur- bances. These goals imply that genes and behaviour have a relation that may be disclosed by exact determination of the human genome and by showing the developmental pathways leading to the expression of the genes in the structures of the human body and in behaviour. Research in behavioural genetics is specifically based on the convic- tion that the relative proportions of genetic and environ- mental influences may be determined, and that this knowledge may be applied in improving human behav- ioural characteristics. Inherent in these convictions is the assumption that genes and environment can somehow contribute to phenotypes independently. However, the basic assumptions of behavioural genetics have evoked strong criticism and doubts as to their scien- tific validity (Allen, 1998; Lewontin, 2001; Lickliter and Honeycutt, 2003; Rose, 1997; Sternberg and Grigorenko, 1999). It has been also somewhat surprising to find that the number of human genes (now estimated at approximately 25 000) does not differ considerably from that of pheno- typically different species such as worms or fruitflies. Fur- thermore, the difference between the genomes of African great apes and humans is only approximately 1%, and all humans share approximately 99.9% of the genome. It is also known that genes vary more within human races than between them. It may be difficult to understand how such small differences in genetic material lead to drastic differ- ences in phenotype and behavioural capabilities. One sug- gestion has been the presence of single nucleotide polymorphisms (SNPs) that vary considerably between in- dividuals and have been assumed to be the basis of the diversity of human functional variation. Methodological Problems in Behavioural Genetics A great leap forwards was made in genetics when the first drafts of the human genome were determined. It has been claimed that this achievement will revolutionize Advanced article Article Contents . Introduction . Methodological Problems in Behavioural Genetics . Genes or Environment as Explanation of Behaviour? . Determination of Genetic Risks Online posting date: 15 th September 2009 ELS subject area: Science and Society How to cite: Ja ¨rvilehto, Timo; and, Lickliter, Robert (September 2009) Behaviour: Role of Genes. In: Encyclopedia of Life Sciences (ELS). John Wiley & Sons, Ltd: Chichester. DOI: 10.1002/9780470015902.a0006181.pub2 ENCYCLOPEDIA OF LIFE SCIENCES & 2009, John Wiley & Sons, Ltd. www.els.net 1