Humankind may have gone about as far as it can go. Our own limits to growth suggest Homo sapiens may have reached some kind of plateau.

A single species that has changed the climate, become the greatest earth-moving force on the planet, and ushered in a new geological era, may also be about to become more aware of its physiological limitations.

French researchers think that although more people are living longer than ever, the record age for any single human may have been set two decades ago by a Frenchwoman, Jeanne Calment, who died in Arles aged 122 years and 164 days.

Tomorrow’s humans may not be able to run much faster than Usain Bolt, the 100 metres Olympic champion and world title holder. Nor are humans – who on average gained 8.3 cms (3.2 inches) in the last 100 years – likely to go on growing taller. At some point humankind may have exhausted its physical potential.

“These traits no longer increase, despite further continuous nutritional, medical and scientific progress. This suggests that modern societies have allowed our species to reach its limits,” said Jean-Francois Toussaint of the Paris Descartes University, who led the study. “We are the first generation to become aware of this.”

And although such constraints are not directly connected to climate change driven by profligate combustion of fossil fuels, what humans achieve is a combination of genetic and environmental limitations.

“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,” he said.

“The current declines in human capacities we can see today are a sign that environmental changes, including climate, are already contributing to the constraints we have to consider.”

Professor Toussaint and his colleagues report in the Journal of Physiology that they worked through an enormous number of studies to track the unprecedented improvements in human capabilities during the 20th century, all of which show signs of a major slowdown in the most recent years.

Soils Overused

They calculated that temperature changes in the last decades may affect human physical limits. They also took into account apparent stagnation in crop yield, the over-exploitation of soils, and human disturbance to the rest of the planet’s biodiversity.

Many of these factors have already been explored. Researchers have established planetary pollution with seemingly indestructible plastic waste on such a scale that it may define a new geological marker for a new era that could be called the Anthropocene.

Human populations are expected to exceed UN forecasts in the coming century and the weight of construction by humankind – the technosphere – has been estimated at 30 trillion metric tons.

These, and the impact on the climate as ever more greenhouse gases are released into the atmosphere from power stations, factory chimneys and exhaust pipes, will leave an indelible mark in the geological record.

Negative Change

Humans evolved in an environment that is now being dramatically altered by human action. But even if records for age, height and athletic performance may endure, many people could hope to go on living healthier lives, and for longer – in a stable climate with reliable food supplies.

But climate is changing, and food yields are threatened. Professor Toussaint thinks that “something has changed, but not for the better. Human height has decreased in the last decade in some African countries; this suggests some societies are no longer able to provide sufficient nutrition for each of their children and maintain the health of their younger inhabitants,” he said.

“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. The utmost challenge is now to maintain these indices at high levels.”


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