The most critical issues confronting Mankind in the 21st Century could be Food / Fuel / Finance, together with the numerous associated problems such as soil fertility, climate change, alternative energies, poverty and social inequity etc. Sustainability (and its purpose) is the key concept here.
However, the ultimate and fundamental question behind all these is: What constitutes Sustainability and Salutogenesis (Health and Wellbeing)? How could these be attained individually and socially that would take consideration of the local, global and even cosmic aspects? A mere Pathogenesis (as compared to Salutogenesis) approach might not solve the problems.
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