COMMENT SOMMES-NOUS DEVENUS 7 MILLIARDS?

L’humanité n’a pas atteint le nombre de 7,4 milliards d’individus du jour au lendemain. Il lui a fallu plus de 3 millions d’années, depuis l’apparition des premiers représentants du genre Homo, pour atteindre une telle population. Avec des hauts et des bas.

L’humanité n’a pas atteint le nombre de 7,4 milliards d’individus du jour au lendemain. Il lui a fallu plus de 3 millions d’années, depuis l’apparition des premiers représentants du genre Homo, pour atteindre une telle population. Avec des hauts et des bas.

Si retracer l’évolution de l’humanité sur plusieurs millions d’années reste une gageure, les spécialistes parviennent à livrer des estimations. Ainsi, ils évaluent qu’à l’aube de l’humanité, l’espèce humaine ne comptait qu’une centaine de milliers d’individus répartis en petits groupes distincts. Il faut attendre 40 000 ans av. J.-C. pour atteindre le million.

Entre ces deux dates, différents scénarios sont avancés. Certains estiment que la population humaine aurait pu croître entre -1,9 Ma et -200 000 ans pour atteindre 1,15 million d’âmes. Et à deux reprises, en -150 000 et -73 000, l’humanité aurait frôlé l’extinction.

Par deux fois proches de l’exctinction

La première fois, il y a environ 150 000 ans, après un épisode glaciaire qui aurait fait chuter la population à quelque 100 000 individus ; la seconde, en 73 000 av. J.-C., après l’éruption du volcan Toba, en Indonésie. Un cataclysme qui aurait réduit l’humanité, selon certaines estimations, à seulement 10 000 représentants.

Pour autant, nous sommes là, et ce malgré les aléas climatiques (périodes glaciaires et interglaciaires), les invasions respectives, les guerres, les maladies (grandes pestes) qui ont ponctué notre histoire.

Entre 6000 et 4000 av. J.-C., au Néolithique, la population sur Terre serait ainsi passée de 7 millions à 30 millions avant d’atteindre, en 2000 av. J.-C., les 100 millions d’individus. Bénéficiant des progrès techniques, de la médecine et de la maîtrise de l’environnement, elle a atteint le milliard en 1800 et les 6 milliards d’humains en 1999.

 

Source : SCIENCE ET VIE

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