needs, our survival, derives from accessing sufficient energy and basic elements for life. This must be achieved through adequate nutrition to satisfy maintenance of metabolic demands for normal activity and the extra needed for reproduction. Energy is also required to deal with variable stressors, such as the avoidance of predation and other threats to survival. Given conditions and environments, various adaptation strategies have been developed for securing energy supply among human beings and other animals.


Human stress: One physiological adaptation mechanism of humans is the acute stress response – the traditionally called fight-or-flight reaction (Cannon 1929) or, as later suggested, also including the tend-and-befriend reaction (Taylor 2006). These bodily adaptation responses are still evoked in humans faced with a perceived threat or stressors, inducing physiological reactions like release of stress hormones, increased pulse rate and redirection of oxygen supply from the vascular system to the muscles instead of the brain (McEwen 2007). Predation, however, is now extremely rare and in case of chronic stress, the physiological stress reactions accumulate and turn maladaptive, as the energy demanding fight-or-flight reactions do not occur and the bodily systems are in a constant alert mode, instead of equilibrium (McEwen 1998). The stress demand on the energy equation and the subsequent wear and tear on the body is therefore an important component of the interactions between health and environmental factors and an example of how originally adaptive mechanisms become harmful in a changed environment. Overcrowding in cities, for example, and lack of green spaces for physical activity and stress recovery, lead to an inability to cope and escape perceived threats, which can feed into the disease burden and the risk of stress related non-communicable diseases (NCDs) (Peen et al. 2010; McEwen and Stellar 1993). Basically, all, organisms require an environment that allows expression of evolutionary adaptation and natural behaviour to maintain health (Okin and Medzhitov 2012).


Overall, speed of change in the environment and biological community affects resilience, sometimes exceeding human


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adaptive capacity. The potential for adaptation is largely determined by scale. For example, microbial communities evolve in minutes or hours and can adapt to rapid environmental changes relatively easily, while maintaining energetic equilibrium. Higher vertebrates, including human beings, on the other hand, require millions of years for functional adaptation and are more likely to be affected by diseases and to decline, or become extinct in phases of very rapid environmental change.


Evidence exists for apparently increasing die-off in certain taxa (Fey et al. 2015) and, in the pan-European context, events reported in musk ox (Kutz et al. 2014) and saiga antelope (Kock 2015) have climate associations with Pasteurella multocida infections and mass mortalities. This is to be expected as these animals are living on the edge, adapted to the extremes of weather on the planet and therefore likely to be indicators of rapidly changing conditions. These anomalies are unlikely to remain the exception with the current speed of environmental change. This puts microorganism at a distinct advantage and may be part of the explanation for the emergence of novel pathogens, epidemics and pandemics, recent examples of which are HIV/AIDS, SARS, bird and swine flu and the Ebola virus.


Ecosystem stress: Although their evolutionary adaptation is slow, humans are a remarkably resilient species in the face of increasing emerging disease events, relying on their dominant access to natural resources, medical technologies and therapeutics to deflect or ameliorate risk – most other animal populations are not so fortunate. For example, a rise in mass die-off events has been reported (Fey et al. 2015; Munson et al. 2008), including of some highly adapted species, especially in the northern temperate latitudes but also in the tropics. These events are most probably a consequence of human induced climate change, causing fundamental ecological shifts, sudden rises in insect vectors and pathogens, in subtle ways stressing animals beyond their evolved adaptive capacities.


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