Songhai chaos control5/1/2023 ![]() It is these tropical diseases, chiefly due to protozoa and helminth metazoans, which began to cripple the development of African societies just at the moment when populations reached the numbers and densities necessary for civilization. As Anderson and May ( 1991) pointed out, to be successful parasites need not necessarily evolve to be harmless, it depends upon the relation between virulence and transmissibility and the cost to the host of evolving resistance. ![]() But those diseases carried by, or directly due, to tropical animal parasites, have not resulted in the same, if any, genetic resistance in man. Probably all are the object of genetic adaptations favouring resistance arising in populations that have long been exposed to them. Most actual and potential human pathogens are endemic to tropical zones and Darlington ( 1969) considered disease had obstructed every racial and cultural development in Africa, the greater part of man’s diseases arising there where man had his origins but climatically indifferent, as they are due to viruses and bacteria which are directly infectious and contagious. In the past Africans were often referred to as prone to psychosomatic illness but new techniques are enabling identification of a whole host of previously unsuspected diseases ranging from debilitating to fatal. This process is experimental and the keywords may be updated as the learning algorithm improves. These keywords were added by machine and not by the authors. As Anderson and May (1991) pointed out, to be successful parasites need not necessarily evolve to be harmless, it depends upon the relation between virulence and transmissibility and the cost to the host of evolving resistance. ![]() Most actual and potential human pathogens are endemic to tropical zones and Darlington (1969) considered disease had obstructed every racial and cultural development in Africa, the greater part of man’s diseases arising there where man had his origins but climatically indifferent, as they are due to viruses and bacteria which are directly infectious and contagious.
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