In humans, a behavioral repertoire and/or cognitive patterns which significantly deviate from those of the majority and which impose a direct threat to one's own life or those of others are considered behavioral or psychiatric disorders. Virtually all psychiatric disorders are almost exclusively human, such as (endogenous) depression, schizophrenia, or drug addiction. In humans, they are highly preserved and often run in pedigrees. In fact, if one or both parents are affected by a certain psychiatric disorder, there is a significantly increased risk for its occurrence in the offspring. Despite intensive research efforts in the last two decades, only relatively minor bits of this inheritance can so far be attributed to genetic risk factors, and thus, to a genetic-based transmission and inheritance (Maher Reference Maher2008). Environmental factors do play a role too, such as stressful life events; but the interaction of genetic with environmental risk factors may not sufficiently explain the high rate of inheritance (Caspi & Moffitt Reference Caspi and Moffitt2006). The lack of a shared genetic base, which may explain behaviorally complex psychiatric disorders (Fanous & Kendler Reference Fanous and Kendler2005), might suggest a cultural transmission of maladaptive behaviors and cognitive patterns (Koopmans & Boomsma Reference Koopmans and Boomsma1996). This transmission may, at least in part, be driven by various forms of teaching.

The propensity for psychoactive drug use, abuse, and addiction may, for example, not only be genetically inherited (Kendler et al. Reference Kendler, Jacobson, Prescott and Neale2003; Müller & Homberg Reference Müller and Homberg2015), but specific abuse-related behaviors may be taught by parents, by other family members, or by members of the peer group (Eissenberg & Balster Reference Eissenberg and Balster2000). Children who are exposed early on to parents who drink alcohol, for example, in order to cope with work stress or to solve relationship problems (Müller & Schumann Reference Müller and Schumann2011), instead of being taught non-drug–incorporating problem-solving strategies, may simply copy these behaviors (Alexander Reference Alexander1990). But parents and peer groups do also actively teach maladaptive behaviors and, thereby, preserve them as a behavioral complex and a part of human culture. They may also teach these behaviors and cognitive patterns, not being aware that they serve as teachers. Teachers may subsequently positively reinforce these newly copied drug-use behaviors in the pupils (Heath Reference Heath2000).

Even more problematic is that these maladaptive behaviors are not only preserved in pedigrees as non-shared cultural knowledge, but may also become shared cultural knowledge when they are “outsourced from human brains” by behavioral storage, copying, and teaching mechanisms. A crucial mechanism for human cultural development is the continuous establishment/creation of new behaviors and their accumulation. Each individual human brain has as a behavioral storage medium only a limited capacity and is unable to store all behaviors and cognitive patterns (including semantic information) that are available in a culture. A major difference to nonhuman species is that humans developed the behavior of coding, storing, and teaching behaviors ex vivo, that is, in other media than the brain. Importantly, these media are virtually unlimited in their storage capacity and may serve as a crucial teaching resource in terms of a shared environment (Müller et al. Reference Müller, Lenz and Kornhuber2012). This includes mechanisms of retrieval and re-incorporation into the actual behavioral complexes of an individual. I argue here that this works also for maladaptive behaviors, which may well lead to psychiatric disorders when copied. As an example, one may consider movies that idealize drug consumption and instrumentalization as behavioral problem-solving strategies (Gibbons et al. Reference Gibbons, Pomery, Gerrard, Sargent, Weng, Wills, Kingsbury, Dal, Worth, Stoolmiller, Tanski and Yeh2010; Hanewinkel et al. Reference Hanewinkel, Sargent, Poelen, Scholte, Florek, Sweeting, Hunt, Karlsdottir, Jonsson, Mathis, Faggiano and Morgenstern2012). Being exposed to them facilitates learning in others in the sense that it provides a behavioral or cognitive scheme that is “authorized” for copying. E x vivo storage and teaching works for behavioral sequences as well as for cognitive patterns, which constitute behavioral response predispositions. Thereby, the definition of teaching behavior should be expanded – only as regards humans, though – to ex vivo sources of behavior and cognitive patterns, including behaviors such as “writing/reading books” or “producing/watching movies” (Wilhite et al. Reference Wilhite, Wilhite and Williams2010). Schizophrenia-associated cognitive patterns may, for example, be found in movies with the “hero” displaying violent paranoid behavior but still serving as a sort of role model. An important feature of this cultural transmission (and accumulation) of maladaptive behaviors and cognitive patterns is that it can be preserved ex vivo and, thereby, jumping several generations, before it is re-activated and actively re-incorporated in vivo into individual behavioral repertoires. Here, one may think about lost ideologies that are rediscovered after centuries and shape new cognitive repertoires and behavior.

One may readily assume that not only adaptive cultural behaviors, but also large parts of the human maladaptive behavioral and cognitive repertoire is transmitted by various types of teaching as outlined by Kline in her excellent article. Thereby, the teaching may be performed at an age before disadvantages of the taught behavior affect biological reproduction. This may explain why the capability of teaching is genetically (and culturally) passed on to the next generation. The negative consequences of the taught behavior only manifest later in life for the teacher. Thus, the maladaptive character may, for example, result in reduced offspring care. Alcohol-addicted parents have fewer resources to actively teach their offspring and to take care of them, because of the development of addiction-related physical and psychological problems (Ward et al. Reference Ward, Lallemand and de Witte2009). At the same time, they teach them significantly more drug-related behaviors to solve everyday problems (e.g., stress drinking). This may constitute a cultural bias towards maladaptive behavior in a pedigree.

Considering these seemingly exclusively human phenomena, I suggest that when discussing teaching as an adaptation in humans which is essential to transmit culture, pleiotropic effects need to be considered in an integrative framework as the individual “price of culture” and its transmission by teaching.