By this view, when mood or anxiety systems malfunction, they do so because of the ways that behavioral rules interact with unusual combinations of experiences and stimuli. A null hypothesis for any such disorder might be that disease cases represent the maladaptive extremes of the population distribution of a complex behavioral trait, determined by the interaction of genetic and environmental variation (Trimmer and colleagues advocate a more nuanced view: while the behaviors associated with mood disorders and anxiety disorders are not themselves adaptive, but may arise from adaptive mechanisms that have become dysregulated by the stochastic inputs they receive. Thus, it is possible for the agent to be misled by an unlikely sequence of successes or failures. Corresponding author. Depression, in the past, may have been selected for since it served as a survival mechanism following ousting from a higher social position. Such strategies include the development of social hierarchies.John Price argued that for hierarchies to be stable, particular, strongly-selected behavioural patterns developed – irritability towards inferiors, anxiety towards superiors, elation on going up the hierarchy and depression on going down.Depression, in the past, may have been selected for since it served as a survival mechanism following ousting from a higher social position. model of depression parallels a model that we independently developed to explore why evolution has left humans vulnerable to pathological anxiety (While these models advance our evolutionary understanding of depression and anxiety, there is plenty left to explain. After all, pursuing unattainable goals is non-adaptive, perhaps fatal, in survival terms.Depressed people may be over committed to goals that are unachievableRottenberg also argues that depressed people don’t lie in bed because they are underachievers – but because they are over-committed to goals that are unachievable. Likewise, anxiety disorders take diverse forms, many of which look different from normal anxiety. Depression is not merely the expression of low mood at the wrong time; it is low mood more prolonged and more intense than what is ever seen in healthy individuals. Might rising rates of depression in the young be accounted for by the setting of increasingly unrealistic goals?A recent paper traced the presence of genes for depression triggered by disruption of circadian rhythms to our Neanderthal ancestors.Intriguingly, sub-Saharan Africans have not inherited any Neanderthal genome – it would be interesting to see whether this type of depression occurs in sub-Saharan Africans and, if so, what its origin might be. To explain depression and anxiety disorders, then, we need to do two things. When recent efforts have been successful, it is best to continue to be active, and when recent efforts have failed, it is best to stop pursuing the opportunities—at least temporarily.

Thus, they suggest, the rumination and anhedonia associated with depression today may be an evolutionarily adaptive relic of our predecessors’ need to solve problems while under stress.Reducing risk to the self and enhancing analytical skills are two potential and not mutually exclusive benefits that could explain the persistence of depression. Our correspondent’s highlights from the symposium are meant as a fair representation of the scientific content presented. In fact, depression does not meet two of the three required criteria from natural selection in order to be evolutionary. The Trimmer et al. Another issue that is important in understanding depression is the idea that natural selection likely has not produced the best possible solution, but instead has found heuristic behavioral rules that only approach or approximate the optimal rule. The views and opinions expressed on this page do not necessarily reflect those of Lundbeck.Rottenberg J. model, an agent faces a series of opportunities which it can either pursue or decline. This also is a difficult problem, but there is a rich history of modeling behavioral heuristcs (In the models we have considered here, behavior arises from an evolved response strategy combined with idiosyncratic individual experience. Evolutionary mismatch (Instead of considering environmental mismatch or looking for ways in which mental illness is adaptive, Trimmer and colleagues model a situation in which an individual needs to regulate its activity in response to information it gets from the environment (In the Trimmer et al. Therefore, while some depressive behaviour may be advantageous for the depressed individual, and is therefore “adaptive” in an immediate sense, it cannot be accurately described as “evolutionary”.

Individual experience is determined by happenstance, but can also be influenced by behavior—creating the possibility of feedback between response strategies and the inputs that they receive.

Department of Biology, University of Washington, Seattle, WA 98125, USA; Email: A little controversial but... Don't you think it's possible that depression and sometimes suicide, is nature's way of saying 'this one is unfit to proceed, next'? The only way for the agent to learn whether things are favorable or not is through trial and error. Adoption of out-group norms provides evidence for social transmission in perinatal care practices among rural Namibian women If all the 'unfit' ones are weeded out, then what remains are the 'strong'?