Nettle et al. provide evidence in support of the insurance hypothesis (IH), which suggests that food insecurity is one key proximate driver of obesity in humans. We resonate with their arguments and agree that the IH likely serves as a partial explanation for obesity in humans. Here we extend their argument and incorporate evidence from another evolutionary theory – life-history theory (LHT; Kaplan & Gangestad Reference Kaplan, Gangestad and Buss2005) – that is consistent with the IH and provides additional insight into both the proximate psychological processes as well as the more ultimate functional considerations that lead to obesity in humans.
LHT is an evolutionary theory that addresses the presence of adaptive mechanisms calibrated early in life to help people maximize their reproductive potential given contingencies in the local ecology. Work in the LHT tradition finds that, across a range of species, the degree of unpredictability in an organism's early-life environment influences behavior in a variety of domains throughout the life course (Simpson et al. Reference Simpson, Griskevicius, Kuo, Sung and Collins2012).
LHT is rooted in the idea that organisms have a finite energy budget that must be allocated in a way that maximizes their overall reproductive fitness. Just as IH highlights the key role of uncertainty in determining the prevalence of obesity, LHT emphasizes that an organism's fitness-maximizing strategy is adaptively calibrated to the level of unpredictability it encounters early in its development. A high level of unpredictability signals to the organism that the future is uncertain, which then increases the extent to which the organism invests in short-term pursuits tied to immediate reproduction. A low level of unpredictability, in contrast, signals that the organism can afford to adopt a reproductive strategy marked by a longer time horizon and greater investment in somatic effort over the long-term. These responses to unpredictability are referred to as fast and slow life-history strategies respectively. Thus, life-history strategies vary on a continuum from fast to slow and are designed strategically to optimize an organism's reproductive success given the level of unpredictability in the environment.
Faster life-history strategies are characterized by behaviors that increase immediate reproduction, such as having more sexual partners earlier in life and a higher number of offspring, investing relatively less in each offspring, and displaying a psychological orientation toward taking risks and seeking short-term rewards (e.g., Griskevicius et al. Reference Griskevicius, Ackerman, Cantú, Delton, Robertson, Simpson, Thompson and Tybur2013). Conversely, slower life-history strategies are characterized by behaviors that emphasize long-term investment in fewer offspring, such as delaying reproduction until later in life, having fewer sexual partners, and delaying immediate gratification in favor of long-term rewards.
LHT also provides insight into adult eating behavior. Recent work provides evidence that low childhood socioeconomic status (SES) is associated with a tendency to eat even when nutrition is not needed, and that this tendency persists into adulthood (Hill et al. Reference Hill, Prokosch, DelPriore, Griskevicius and Kramer2016; Olson et al. Reference Olson, Bove and Miller2007). In humans, the conditions typically associated with low-SES environments include uncertainty and resource scarcity and thus reflect the type of harsh and unpredictable conditions that promote the development of a faster life-history strategy. Growing up in an environment in which access to an adequate food supply is relatively uncertain promotes eating whenever food is available, regardless of energy need. If the availability of food in the future is relatively uncertain, it may behoove one to consume as much as possible when one has access to it.
Although this strategy may be adaptive when embedded in unpredictable low-SES environments, it is less likely to be adaptive in high-SES environments, which tend to be more stable and characterized by greater access to nourishment. However, LHT suggests that the life-history strategy one develops early in life tends to persist into adulthood. One's life-history strategy is calibrated early in development and often continues to influence behavior across the life course, even if the qualities of one's current environment change (Simpson et al. Reference Simpson, Griskevicius, Kuo, Sung and Collins2012). Thus, even if individuals who grew up in a low-SES environment are able to improve their circumstances and transition into a more stable, higher-SES environment, their faster life-history strategy still tends to shape their behavior. This ongoing reliance on a faster life-history strategy may, in turn, lead to a continued tendency to eat regardless of level of energy need. This tendency would stand in contrast to that of their counterparts who grew up in higher-SES environments, who are more likely to calibrate their eating behavior to their current level of hunger.
Although initial evidence provides insight into how one's early-life environment can affect adult eating behavior, one limitation of existing work is that it does not test whether early developmental experiences associated with unpredictability are linked specifically to adulthood obesity.
Recent data from our lab speak directly to the link between early-life unpredictability and likelihood of obesity in adulthood. A sample of 400 community participants reported their level of early-life unpredictability, provided a measure of their life-history strategy, described their current engagement in weight management behaviors, and reported their current height and weight (from which we were able to calculate their body mass index). The data closely fit a serial mediation model in which exposure to unpredictability early in development led people to adopt a relatively fast life-history strategy, which in turn predicted reduced engagement in weight management behaviors and, ultimately, a higher likelihood of experiencing obesity in adulthood (Maner et al., Reference Maner, Dittmann, Meltzer and McNultyunder review). These findings suggest that early-life environmental unpredictability may play a key role in determining eating behavior and obesity in adulthood.
These data, as well as other recent work in the LHT tradition, provide evidence consistent with the hypothesis that many behaviors in adulthood – including those that pertain to eating – are adaptively calibrated to environments experienced earlier during development. These findings complement and extend the IH by shedding light on how early-life exposure to environmental unpredictability influences eating behavior and obesity in adulthood. We believe the IH and LHT can inform one another and together provide a richer portrait of life span influences on eating behavior and obesity.
Nettle et al. provide evidence in support of the insurance hypothesis (IH), which suggests that food insecurity is one key proximate driver of obesity in humans. We resonate with their arguments and agree that the IH likely serves as a partial explanation for obesity in humans. Here we extend their argument and incorporate evidence from another evolutionary theory – life-history theory (LHT; Kaplan & Gangestad Reference Kaplan, Gangestad and Buss2005) – that is consistent with the IH and provides additional insight into both the proximate psychological processes as well as the more ultimate functional considerations that lead to obesity in humans.
LHT is an evolutionary theory that addresses the presence of adaptive mechanisms calibrated early in life to help people maximize their reproductive potential given contingencies in the local ecology. Work in the LHT tradition finds that, across a range of species, the degree of unpredictability in an organism's early-life environment influences behavior in a variety of domains throughout the life course (Simpson et al. Reference Simpson, Griskevicius, Kuo, Sung and Collins2012).
LHT is rooted in the idea that organisms have a finite energy budget that must be allocated in a way that maximizes their overall reproductive fitness. Just as IH highlights the key role of uncertainty in determining the prevalence of obesity, LHT emphasizes that an organism's fitness-maximizing strategy is adaptively calibrated to the level of unpredictability it encounters early in its development. A high level of unpredictability signals to the organism that the future is uncertain, which then increases the extent to which the organism invests in short-term pursuits tied to immediate reproduction. A low level of unpredictability, in contrast, signals that the organism can afford to adopt a reproductive strategy marked by a longer time horizon and greater investment in somatic effort over the long-term. These responses to unpredictability are referred to as fast and slow life-history strategies respectively. Thus, life-history strategies vary on a continuum from fast to slow and are designed strategically to optimize an organism's reproductive success given the level of unpredictability in the environment.
Faster life-history strategies are characterized by behaviors that increase immediate reproduction, such as having more sexual partners earlier in life and a higher number of offspring, investing relatively less in each offspring, and displaying a psychological orientation toward taking risks and seeking short-term rewards (e.g., Griskevicius et al. Reference Griskevicius, Ackerman, Cantú, Delton, Robertson, Simpson, Thompson and Tybur2013). Conversely, slower life-history strategies are characterized by behaviors that emphasize long-term investment in fewer offspring, such as delaying reproduction until later in life, having fewer sexual partners, and delaying immediate gratification in favor of long-term rewards.
LHT also provides insight into adult eating behavior. Recent work provides evidence that low childhood socioeconomic status (SES) is associated with a tendency to eat even when nutrition is not needed, and that this tendency persists into adulthood (Hill et al. Reference Hill, Prokosch, DelPriore, Griskevicius and Kramer2016; Olson et al. Reference Olson, Bove and Miller2007). In humans, the conditions typically associated with low-SES environments include uncertainty and resource scarcity and thus reflect the type of harsh and unpredictable conditions that promote the development of a faster life-history strategy. Growing up in an environment in which access to an adequate food supply is relatively uncertain promotes eating whenever food is available, regardless of energy need. If the availability of food in the future is relatively uncertain, it may behoove one to consume as much as possible when one has access to it.
Although this strategy may be adaptive when embedded in unpredictable low-SES environments, it is less likely to be adaptive in high-SES environments, which tend to be more stable and characterized by greater access to nourishment. However, LHT suggests that the life-history strategy one develops early in life tends to persist into adulthood. One's life-history strategy is calibrated early in development and often continues to influence behavior across the life course, even if the qualities of one's current environment change (Simpson et al. Reference Simpson, Griskevicius, Kuo, Sung and Collins2012). Thus, even if individuals who grew up in a low-SES environment are able to improve their circumstances and transition into a more stable, higher-SES environment, their faster life-history strategy still tends to shape their behavior. This ongoing reliance on a faster life-history strategy may, in turn, lead to a continued tendency to eat regardless of level of energy need. This tendency would stand in contrast to that of their counterparts who grew up in higher-SES environments, who are more likely to calibrate their eating behavior to their current level of hunger.
Although initial evidence provides insight into how one's early-life environment can affect adult eating behavior, one limitation of existing work is that it does not test whether early developmental experiences associated with unpredictability are linked specifically to adulthood obesity.
Recent data from our lab speak directly to the link between early-life unpredictability and likelihood of obesity in adulthood. A sample of 400 community participants reported their level of early-life unpredictability, provided a measure of their life-history strategy, described their current engagement in weight management behaviors, and reported their current height and weight (from which we were able to calculate their body mass index). The data closely fit a serial mediation model in which exposure to unpredictability early in development led people to adopt a relatively fast life-history strategy, which in turn predicted reduced engagement in weight management behaviors and, ultimately, a higher likelihood of experiencing obesity in adulthood (Maner et al., Reference Maner, Dittmann, Meltzer and McNultyunder review). These findings suggest that early-life environmental unpredictability may play a key role in determining eating behavior and obesity in adulthood.
These data, as well as other recent work in the LHT tradition, provide evidence consistent with the hypothesis that many behaviors in adulthood – including those that pertain to eating – are adaptively calibrated to environments experienced earlier during development. These findings complement and extend the IH by shedding light on how early-life exposure to environmental unpredictability influences eating behavior and obesity in adulthood. We believe the IH and LHT can inform one another and together provide a richer portrait of life span influences on eating behavior and obesity.