Every four years, the world turns its attention to the Olympics to see competitors go "faster, higher, stronger." We tend to take this trajectory for granted, and average human height and life expectancy have played along by increasing significantly over the past two centuries. But the human body obviously has biological limits. A review of 120 years of historical records now suggests those limits may have already been reached – and if we aren't careful things could start going backwards.
The review carried out by a transdisciplinary research team from across France studied historical data on lifespan, sport and height collected since the nineteenth century. The goal was to gain a better understanding of how human physiology had progressed over the last 10 generations, and the team says the records suggest that these traits have plateaued and there are maximum limits that cannot be exceeded.
"These traits no longer increase, despite further continuous nutritional, medical, and scientific progress," says Professor Jean-François Toussaint from Paris Descartes University, France. "This suggests that modern societies have allowed our species to reach its limits. We are the first generation to become aware of this."
The researchers say that instead of the tallest humans getting taller, the fastest getting faster and the longest-living getting older, the best we can hope for is an increase in the proportion of the population reaching the existing limits for these traits. As a result, there would be more and more people living to the current highest life expectancy (around 85 to 95 years, with 115 to 125 years the limit for maximum longevity) and growing to maximum current heights (about 200 cm/6.5 ft), while fewer and fewer sporting records would be broken.
However, that's a best-case scenario and there could actually be a decline in life-expectancy, height and sporting performance due to a combination of genetic limitations and environmental factors, such as climate change. Prof. Toussaint points out that such a decline of human height has already occurred in some African countries due to a lack of nutrition available to children.
"This will be one of the biggest challenges of this century as the added pressure from anthropogenic activities will be responsible for damaging effects on human health and the environment," predicts Prof. Toussaint. "The current declines in human capacities we can see today are a sign that environmental changes, including climate, are already contributing to the increasing constraints we now have to consider."
The researchers hope their findings will prompt policymakers to pursue strategies that will increase quality of life and allow the greatest proportion of the population possible to reach their maximum biological limits.
"Now that we know the limits of the human species, this can act as a clear goal for nations to ensure that human capacities reach their highest possible values for most of the population. With escalating environmental constraints, this may cost increasingly more energy and investment in order to balance the rising ecosystem pressures. However, if successful, we then should observe an incremental rise in mean values of height, lifespan and most human biomarkers. However, Prof. Toussaint warns the primary concern should be to arrest any future decline, saying, "The utmost challenge is now to maintain these indices at high levels."
The team's paper appears in the journal Frontiers in Physiology.
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