ASPECTS OF MAN'S ADAPTATION IN THE TROPICS 



mama) has very high uptake levels 

 of radioactive iodine, levels that, in 

 civilized areas, are characteristic of 

 people with quite large goiters. It 

 begins to appear that the development 

 of goiter in the so-called endemic- 

 areas involves more than simple io- 

 dine shortage, that there is some 

 environmental factor which interferes 

 with the utilization of iodine but 

 which can be offset by the use of 

 doses of iodine. 



Diabetes — A second example is 

 provided by diabetes mellitus. In 

 some of the Indian groups of south- 

 western United States, diabetes is 

 appearing with a great frequency 

 and many complications. Although 

 the evidence is scanty, the disease 

 does not seem to be particularly 



prevalent among unacculturated In- 

 dians. The most obvious difference 

 between Indian groups with high 

 rates of diabetes and those with low 

 rates is the greater amount of obesity 

 and the lesser amount of exercise of 

 the former. Thus, diabetes mellitus 

 may represent a breakdown in adap- 

 tation to a changing way of life. 



Caries — For a third and final ex- 

 ample of how the adaptations of 

 primitive man in the tropics are 

 altered by acculturation, one might 

 mention the well-known example of 

 caries. Most relatively untouched 

 groups of primitives are almost 

 caries-free. But within a few years 

 of acculturation, caries often become 

 rampant. The reason is still not 

 clear. Understanding of any of these 



three phenomena would contribute 

 greatly to our knowledge of man's 

 adaptation in the tropics as well as in 

 other regions. 



There is a widespread feeling that, 

 given today's rapid changes in man's 

 way of life, the selective forces that 

 shaped him and brought him thus far 

 are rapidly being altered. Studies 

 such as the ones briefly sketched here 

 can provide concrete insight into 

 the way these forces are being altered. 

 Many of the conclusions will have to 

 be inferential rather than demon- 

 strated. Even so, it is hoped that 

 such studies will provide a perspec- 

 tive on the extent of the changes now 

 occurring in man's way of life and 

 some of its problems and conse- 

 quences. 



ADAPTATION TO HIGH ALTITUDE 



In the autumn of 1967, two inter- 

 national conferences were held to 

 assess the state of knowledge about 

 high-altitude effects on man. One of 

 these was sponsored by the U.S. 

 Army Medical Research and Devel- 

 opment Command, the other by the 

 World Health Organization (WHO), 

 the Pan American Health Organiza- 

 tion (PAHO), and the U.S. Interna- 

 tional Biological Program (IBP). Be- 

 tween the two conferences, all major 

 laboratories and research groups 

 working in this problem area were 

 represented. Results were reported 

 of a decade of intensified research 

 effort in the United States and abroad. 



Information Level as of 1967 



The basic physiological and psy- 

 chological effects of altitude on low- 

 landers moving rapidly to high 

 altitudes had been described and 

 verified by the late 1950's. In the 

 early 1960's, research proceeded 

 along these lines: 



1. Intensified physiological re- 

 search on the consequences of 



moving men rapidly from low 

 to high altitude. 



2. Study of the physiology and 

 general biology of high-altitude 

 natives in Peru, Nepal, and the 

 United States. 



3. Investigation of medical prob- 

 lems peculiar to men living at 

 high altitude. 



The details of the findings avail- 

 able from these pre-1968 studies are 

 too lengthy to cite in a short report, 

 but some of the highlights were: 



1. A detailed description of the 

 physiological and psychological 

 limits of low-altitude man's al- 

 titude tolerance. This included 

 a partial knowledge of how 

 much improvement could be 

 expected in performance ca- 

 pability with time and some 

 knowledge about the utility of 

 drugs in modifying altitude 

 tolerance. 



2. The study of high-altitude na- 

 tives demonstrated them to be 



different from lowlanders in a 

 number of general biological 

 and specific physiological pa- 

 rameters. These differences in- 

 cluded an increased incidence 

 of neonatal deaths, different 

 growth patterns, an oxygen- 

 consumption capacity above 

 that of the lowlanders going to 

 altitude even for an extended 

 time (see Figure XI-4), and, fi- 

 nally, a number of unusual dis- 

 ease characteristics including a 

 remarkable lack of adult cardio- 

 vascular disease. 



3. The study of medical problems 

 at altitude had provided a basic 

 physiological description of the 

 two direct altitude-related dis- 

 eases. These are an acute form 

 producing high-altitude pul- 

 monary edema (HAPE) and a 

 chronic form which causes a 

 runaway polycythemia. Anes- 

 thesiological and surgical proce- 

 dures suitable to high altitude 

 had been partially developed 

 and it had been discovered that 

 many drugs have altered action 



379 



