Natural selection has shaped our body and mind for life as paleolithic hunter-gatherers (HGs). Hominids have been living in that way for millions of years after they diverged from the chimpansees. Agriculture only appeared about 10,000 years ago in the Middle East, and even later in most other parts of the world. Therefore, our genes have not really had the time to adapt to the lifestyle of farmers or industrial workers: they still prepare us for a life of hunting and gathering.
This means that there is a fundamental misadaptation between our present lifestyle and the one that our genes expect. This discord can explain a host of so-called "diseases of civilisation": coronary heart disease, obesity, cancer, diabetes, Alzheimer, depression, chronic stress, anxiety, ADHD, etc. These diseases needlessly degrade body and mind, while significantly reducing our life expectancy and sense of well-being.
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