"Normal human lifespan" is a relative notion. Here, we can see that even in the present day, life expectancy is different depending on where you are in the world. Many of the factors that influence life expectancy relate to quality of life; clean food and water, sanitation, level and quality of Healthcare, etc.

Why do you feel this is "knowledge?" You're asking a question about several ideas you've connected. That doesn't make it knowledge, especially given the difficulty in verifying, so more aligns with "belief," and it may very well be a common belief.

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