Above 30 C the mortality increases by 30

What is the common point between a shrew of 5 grams and a 25-ton humpback whale "Both are mammals." This is true, but it is not the correct answer. "They take care of their young." Well seen, but this is not it. Everything seems to separate these two animals: size, environment, food, life expectancy. A very unexpected parameter together: their heart beats approximately 1 billion times in their lifetime. The small rodent, always restless and worried, lives about three years. It imposes on its exciting pace of hell: 600 beats per minute. Just halfway between the Hummingbird, which exceeds the 1,000 pulses per minute during the hover, and chicken that displays 270 beats per minute. The slow and majestic humpback whale merely a pulse all 4 to 5 seconds. She lives on average ninety ten years. The heart beat in a lifetime billion thus appears to be a widespread physiological limit in the world of the living.

Humans are apparently the only to escape this rule. "Our heart beats about 40 million times in a year, which represents 3-4 billion pulses in 80 years", says biologist Belgian Albert Gold-better in his book "The life" oscillatory (Odile Jacob). But this success "against nature" is very recent. For millennia, a human life expectancy was between twenty and thirty years. It is only at the beginning of the 20th century that humanity has escaped to the "curse of the billion". At the Institute of biomedical research and epidemiology of sport (Irmes), Dr. Jean-François Toussaint looks long at these notions of physiological limits. For him, no doubt, the golden age is behind us, and the Olympic motto "citius, altius fortius" is to the radius of the junk. "L es progress is slow and the curve reaches an asymptote.". Look at the evolution of the world records in the Olympic disciplines. The same is true of our average life expectancy, which seems to set a ceiling to ninety ten years.

The Irmes is the Office of the national Institute of sport (Insep), where train the French champions aimed a medal. Sport is a gold mine for statisticians. Since a hundred years, all records are listed, and these data confirm the progress made. Between 1920 and today, women's sprint athletes made the best time over 100 metres flat 13 seconds 10,49 seconds. Progress is impressive. But since 1990, it is flat calm. Except chemical or mechanical artifice, it seems that man has indeed reached "the maximum speed which allows him to escape predators and determines its individual survival", according to the formula built by Jerry Husak evolution specialist.

These data also allow to verify a fact known to all: the body is a thermal machine which must evacuate the calories produced during the effort. 50 Fastest French sprinters have managed their best times in the cool evenings of the beginning of September and the performance of the Ethiopian marathoner Haile Gebreselassie vary greatly with temperature. Two and a half minutes earned on the 42.195 km marathon from 23 C to 13 C. In fact, the ideal temperature of endurance races is 11 C. This optimum promotes evacuation of calories, while allowing the two essential components of the muscle contraction (actin and myosin) smoothly. This "pressure cooker effect" occurs in the daily mortality curves in the hexagon. As soon as it leaves the optimal area (between 18 and 21 C), the death soars. Above 30 C, the mortality increases by 30. And it doubles when the mercury drops below - 15 C. "The body is optimized to work well at 20 C", summarizes Jean-François Toussaint.

These physiological barriers occur in other areas According to data from the Irmes, grain yield, growth rates and life expectancy have also reached their peak. With his sidekick biologist Bernard Swynghedauw, Jean-François Toussaint wondered how to keep "the strides of humanity in the course of the last generations". A drop of water in the history of life that warrants, according to these two experts, to develop a pedagogy of the limit. "