There's lots of talk about finding "a gene for aggression" or "a gene for homosexuality" etc. I'm less interested in cases where the results are clearly ambiguous like in most (if not all) human studies. Rather I'd like to know what people think we even mean when we refer to a gene as being the gene "for behavior X". Some examples: In Drosophila melanogaster there is a gene called fruitless (fru). When mutated, this gene causes a set of behaviors in fruitflies that we might recognize as similar to homosexuality. Fixed action patterns like courtship in Drosophila appear to be highly genetically determined with little environmental effect on how and when they are performed. This is in contrast to most human behaviors which are more influenced by environmental or other factors. Birdsong is another good example of a behavior that is inflenced by genetics but highly environment dependent (in most species anyway) birds typically learn their songs from other birds. However, this process can be disrupted by genetic methods. Also in Drosophila (and many other organisms) there are the so-called "clock genes". These include period (per), timeless (tim) and doubletime (dbt). Mutations of these genes lead to changes in the animal's rest/activity cycles. That is, they change the animal's behavior. --- The existence of fixed action patterns like Drosophila courtship which are highly complex behaviors that can be disrupted by the mutation of a single gene should be reason enough to consider "the gene for behavior X" talk as worthy of examination. We can distinguish several different ways in which genes might influence behavior. They migh control the actual instance of the behavior while the animal performs it. Alternatively, they might be active only during development during which time they direct the forming of specialized neural circuits either for performing the behavior of for potentiating the likelihood of performing the behavior. After the animal is mature these genes may no longer be active. For a particularly interesting review article on this topic check out: --- I'd like to know what other people think about a few questions. 1) Does finding a gene that influences a complex fixed action pattern constitute finding "a gene for a behavior"? Or is this somehow less liberally worrisome? 2) Do you know of any instances where genes have been shown to be causal of the performance of a complex behavior that is not a fixed action pattern? Do you expect that we will find uncontroversial examples of this? 3) What do we really mean when we say that a gene controls a behavior?