The health prospects of humanity are influenced by many things. There are extrinsic factors like poverty, violence, and infectious disease that can cause humans to die. There are also intrinsic factors, like the constraints of our biology (e.g. aging). The role these different factors play in causing disease and death in the world changes over time. The greater success we have with combating extrinsic risks, the greater the impact intrinsic risks have on our health prospects.
I have been mining this article for data on global mortality between 1970-2010 to help capture how the health challenges facing human populations have changed over time. I decided it would be helpful to compare the number of human deaths that occur when the force of natural selection is working at 100% (the pre-reproductive stage) with the death rates when the force of natural selection is working at 0% (after the "biological warranty period" has expired, approximately age 70 for our species). As such these two categories are biologically meaningful age windows. They effectively illustrate the priority natural selection places on reproductive fitness over the longevity of a parent (which becomes most evident by 2010 when extrinsic risk factors for both age groups are lowered, but with significant differences in mortality numbers). We cannot hope to tackle the health challenges of today and tomorrow without an understanding of how natural selection impacts the health prospects of today's aging populations.
The first chart below compares the number of deaths, in thousands, of people age ≤ 14 with those who die age ≥70 in 1970 and 2010. This gives us a good sense of how health challenges have changed over the past 4 decades. As public health measures and material prosperity improved, deaths early in life have been reduced by half. But the story at the other end of the lifespan is very different. The chronic diseases of late life are the leading causes of death in the world today. Promoting health in late life is thus a significant global health challenge today and for the future. The health innovations needed to promote health in late life will need to be very different from those that have proved effective in helping to reduce death and disease in the pre-reproductive stage of life (when the force of natural selection is 100%).
The point of showing these two graphs? Answer: the stakes have never been higher for humanity than they are now for pursuing Darwinian medicine.
Some common reactions people might tend to have to the message I convey here (these are common comments I have heard many times, even from researchers in the health sciences):
1. The levels of early life mortality today are a tragedy and should be lower.
My response: I completely agree! So pointing out that there are significant health challenges in late life does not mean that significant challenges do not remain with respect to tackling disease and death in early life (though we should acknowledge that the trend for early life mortality is a declining (not inclining) one).
2. We should divert all resources to combating early life mortality (which I have actually heard researchers suggest)
My response: we should aspire to promote health at all stages of the human lifespan. It is irrational to think that we should only care about saving the lives of children when they are young, but not give a damn about their health prospects when they are older. That is simply ageism.
3. The chronic diseases of late life are only a problem for the world's richest countries.
My response: This attitude is not grounded in the empirical data. Furthermore, it rests on a very simplistic and mistaken view of human biology. It is on my "top 5" list of dogmas that must be eliminated if we hope to create a more humane and rational world.
Colin Farrelly is currently Queen's National Scholar in the Dept of Political Studies at Queen's University. His most recent book is entitled Justice, Democracy and Reasonable Agreement.
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