Can ideas about the regulation of body mass in birds be used to explain the breakdown of regulation associated with obesity and anorexia in humans? There is no evidence to think so. Medicine can always benefit from the application of evolutionary ecology ideas, but we must be prepared to dismiss these ideas when they just do not fit the data.

We suggest that social factors are key to explain the missing link between food insecurity and obesity in children. Parents and public institutions are children's nutritional gatekeepers. They protect children from food insecurity by trimming down their consumption or by institutional support. To gauge children's food insecurity, evaluations across the different nutritional gatekeepers need to be integrated.

The existence of specific polymorphisms in genes of key hormones of the energy homeostasis network that have been shown to predispose to obesity and the so-called metabolic syndrome provides further biological support for the proposed insurance hypothesis. In a broader sense, such polymorphisms can be understood as biological imprints of an evolutionarily successful minimax strategy employed by ancient Homo sapiens subpopulations in a one-player game against nature.

The insurance hypothesis does not address important factors known to contribute to obesity levels in all persons, not just adult women in the industrialized world. These include psychological determinants of eating behaviours, the decline in physical activity leading to a negative energy balance, the dense built environment, pervasive food marketing, and the increased availability of energy-dense, nutrient-poor food.

Starvation arouses evolved protective mechanisms including binge eating and increased metabolic efficiency and fat storage. When aroused by dieting, the experiences of out-of-control eating, increased appetite, and increased fat storage arouse greater fears of obesity, spurring renewed attempts to restrict intake severely. The resulting positive feedback cycle escalates into bulimia for many, and anorexia in a few.

Health messages designed to address obesity are typically focused on the long-term benefits of eating healthy food. However, according to the insurance hypothesis, obese people are food insecure, and this causes them to be overly concerned about short-term consumption. As such, it is necessary to rethink public health messaging and consider how to reduce short-term insecurity by eating healthy food.

An effect of the long-term cycle of industrial and post-industrial global development is the increasingly generalized access to abundant and diversified food sources. This poses a substantial problem of self-regulation that mainly affects the less affluent and whose failures may play an important role in the explanation of the increasing social incidence of overweight and obesity problems.

Evidence has accumulated in support of the notion that changes in household-level financial uncertainty (or “economic insecurity”) may be an important fundamental cause of the global obesity epidemic. The timing and spatial/demographic incidence of the obesity epidemic suggest that economic policies aimed at expanding economic freedom may have inadvertently shifted risk to households, thereby generating a costly public health problem.

Consistent with the insurance hypothesis, research shows that when children experience restricted access to food, they display increased intake when restrictions are lifted. This effect appears more robust for girls compared to boys, and for children with lower levels of inhibitory control. The insurance hypothesis has potentially important implications for parental feeding practices.

Nettle et al. miss the crucial difference between adaptive models of storing energy and explanations for the pathological metabolic state of obesity. I suggest that the association of food insecurity with obesity in women from industrialized settings is most likely due to reverse causation: Poverty reduces agency to resist obesogenic foods, and this scenario is compounded by perturbations of insulin metabolism stemming from high adiposity and lipogenic diets.

We reflect on the major issues raised by a thoughtful and diverse set of commentaries on our target article. We draw attention to the need to differentiate between ultimate and proximate explanation; the insurance hypothesis (IH) needs to be understood as an ultimate-level argument, although we welcome the various suggestions made about proximate mechanisms. Much of this response is concerned with clarifying the interrelationships between adaptationist explanations like the IH, constraint explanations, and dysfunction explanations, in understanding obesity. We also re-examine the empirical evidence base, concurring that it is equivocal and only partially supportive. Several commentators offer additional supporting evidence, whereas others propose alternative explanations for the evidence we reviewed and suggest ways that our current knowledge could be strengthened. Finally, we take the opportunity to clarify some of the assumptions and predictions of our formal model.

The way the cognitive system scans the visual environment for relevant information – visual search in short – has been a long-standing central topic in vision science. From its inception as a research topic, and despite a number of promising alternative perspectives, the study of visual search has been governed by the assumption that a search proceeds on the basis of individual items (whether processed in parallel or not). This has led to the additional assumptions that shallow search slopes (at most a few tens of milliseconds per item for target-present trials) are most informative about the underlying process, and that eye movements are an epiphenomenon that can be safely ignored. We argue that the evidence now overwhelmingly favours an approach that takes fixations, not individual items, as its central unit. Within fixations, items are processed in parallel, and the functional field of view determines how many fixations are needed. In this type of theoretical framework, there is a direct connection between target discrimination difficulty, fixations, and reaction time (RT) measures. It therefore promises a more fundamental understanding of visual search by offering a unified account of both eye movement and manual response behaviour across the entire range of observed search efficiency, and provides new directions for research. A high-level conceptual simulation with just one free and four fixed parameters shows the viability of this approach.

Rejecting information-processing-based theory permits the merging of a top-down analysis of visual search tasks with a bottom-up analysis of brain structure and function. This reveals the true nature of the functional visual field and its precise role in the conduct of visual search tasks. The merits of such analyses over the traditional methods of the authors are described.

Some previous accounts of visual search have emphasized covert attention at the expense of eye movements, and others have focused on eye movements while ignoring covert attention. Both selection mechanisms are likely to contribute to many searches, and a full account of search will probably need to explain how the two interact to find visual targets.

When studying visual search, item-based approaches using synthetic targets and distractors limit the real-world applicability of results. Everyday visual search can be impaired in patients with common eye diseases like glaucoma and age-related macular degeneration. We highlight some results in the literature that suggest assessment of real-word search tasks in these patients could be clinically useful.

Many parts of the medical image are never fixated when a radiologist searches for cancer nodules. Experts are able to use peripheral vision very efficiently. The size of the functional visual field appears to increase according to the level of expertise. However, searching a medical image diverges, in a puzzling way, from the typical search for a target feature in the laboratory.

Hulleman & Olivers (H&O) reject item-based serial models of visual search, and they suggest that items are processed equally and globally during each fixation period. However, neuroscientific studies have shown that attentional biases can emerge in parallel but in a spatially selective item-based fashion. Even within a parallel architecture for visual search, the item remains the critical unit of selection.

This call to revolution in theories of visual search does not go far enough. Treating fixations as uniform is an oversimplification that obscures the critical role of the mind. We remind readers that what happens during a fixation depends on mindset, as shown in studies of search strategy and of humans' ability to rapidly resume search following an interruption.

A framework where only the size of the functional visual field of fixations can vary is hardly able to explain natural visual-search behavior. In real-world search tasks, context guides eye movements, and task-irrelevant social stimuli may capture the gaze.

Hulleman & Olivers (H&O) make a much-needed stride forward for a better understanding of visual search behavior by rejecting theories based on discrete stimulus items. I propose that the framework could be further enhanced by clearly delineating distinct mechanisms for attention guidance, selection, and enhancement during visual search, instead of conflating them into a single functional field of view.