Ecologic and ethnic adaptations

ENVIilOh’hIENTAL

HESEAHCH

2, 417-422

Ecologic

( 1969)

and

Ethnic

Adaptations

J. A. HILDES

During the first sessions of this Symposium, the biochemists and pharmacologists gave us some insight into the effects of c~n\lironmcntal hazards on men and on experimental animals. Other aspects of the study of health hazards of the environment have been indicated by Dr. Aschoff and by Dr. Prossernamely, the adaptations which occur to cnvironmcntal conditions. This is the area we are considering now. \Vc are primarily concerned with the ccosystcm constituted by man in relation to his total environment. According to Dobzhansky (S), man’s total environment comprises: i 1) the physical environment-tcmperatl~re, humidity, etc.; (2) the biologic environment-the organisms which serve as food, as parasites, and as competitors; (3) the cultural or social environment-which man, amongst the other animals, has developed to a unique degree; and (4) the genetic cnvironmentthe genetic makerlp of the individual. We have heard about genetic adaptation. In addition to the capacity for wolutionarv change and progress by genetic selection, mammalian organisms, in&ding man. have a “phenotypic plasticity,” \vhich allows adaptations to occur within thcslife span of the individual (16). Thrsc may be changes of acclimation or acclilnatization, as defined bv Prosscr. Some of thcsc are reversible shortterm effects such as the physiologic effects of mlnwilar training which ma! be induced at any phase of the life span. Other environmental stresses may induct certain adaptivre rcsponscs only if tllc'y arc opc‘rative in the early stages of development of the individual, and mav lw relatively irreversible. Jlan's phenotypic plasticity estends to an arca of such importanw to him as to warrant special considcrntion-the adaptabilitv of the central nervous system which is the basis for behavioral and cultural responses to the environment, that is, lc,arning and social behavior (3). This type of adaptation is not onIy available to the individual, but it is capable of nongcwetic transmission throughout the population and from generation to generation. Thrreforc, it can effect changes in a population very much faster than genetically dependent adaptation. as Dr. Li’ so emphatically pointed out. TO recapitulate, we have physiologic, relatively short-term adaptations, both acclimation and acclimatization: developmental adaptations; and cultural adaptations, by which individuals react to the physical, biological. and cultural aspects of their environment.

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The cultural adaptations are those on which man chiefly relies for the very rapid adjustments necessitated by the considerable changes in the environment which he himself incluccs. Even allowing for our egocentricity. as Dr. IIardy brought out in the discussion, man is unique: hc is the dominant animal in the world today, and through the eorltrol of energy hc has wrought glcut c>nvironmental changes, including the elimination of other spc‘cicas alld the development of some new ones. These tl-ansformations of the cnvironmcnt arc usually undertaken without much thought of their ecologic conscqlencc’s; in fact, some of the cons~~qucnces may be unforc~secablc. Roth thcl biologic and the cultural adaptations have genc>tically determined limitations, and may thccmselves influence genetic selc&ons. Therefore, studies to scparatc out the various components of man’s aclaptivt, responses to his total environment may bc cqcctcd to bc somewhat complex. Ncverthcless, onr purpose at this Symposium is not onI!. to outline some of the known cnvironmental stresses and man’s capacity for adaptive responses to them, but also to consider the types of investigation which may be needrd to separate out the physiologic. cultural, and genetic components of the adaptive proacsses.

There is abundant e\,idcnce that man has the capacity to adapt to many facets of the physical environment. Reference has been previously made at this Symposium to the “Handbook of Physiology,” c&ted by Dill et al. (4). to which some of the participants at this Symposium have contributed. Temperature and altitude are two of the cnvironmcmtal factors for which the evidence of adaptation is most abundant, and wc will be hearing from Dr. Wyndham, later, on adaptations to heat and to cold. The same Handbook contained chapters outlining the statr of knowleclgcl with rc>gartl to solar radiation, light intensity, motion, and noise. We havcl heard from Dr. .4schoff about adaptive biologic rhythms. At the prcsc’nt time, there is little evidrncc of physiologic adaptation to ionizing radiations or to air pollution. However, cvcn for environmental temperature and barometric pressure, which have been areas of active interest and investigation for some years, our knowledge is rather fragmentary; some of the phenomena still require full description. mechanisms of action arc’ not all clear, and the variability of individuals and populations are important aspects requiring study. ground too far, I will comment briefly Without encroaching on Wyndham’s on adaptations to environmental temperature to illustrate some of the points I wish to make. In a review of the studies of cold tolerance which have been made on primitive man, Hammel found the differences between the various ethnic groups impressive (7). He speculated that these differences were probably due to evolutionary progression based on genetic selection. However, Weiner (15), in discussing Hammel’s paper, pointed out that, if this is so, it is very different from heat adaptation, for which no evidence of genetic differences between races exists. The differences expounded by Dr. Prosser between acclimation and acclima-

ECOLOGIC

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ETHNIC

hDAPT.%TlONS

419

tization are of importance in considering responws t0 cold. Adaptations to cold may not be direct and specific consequences of cold exposure per se. They are still “:~&ptive” if they confer an advantage on the individual or the population. For clsample, the dietary habits of Eskimos, with respect to the high intake of protein, may well be one basis for the incwase in mc+abolism which confws a distinct advantage in cold esposnrc ( la). Similarly. the reccwt studies 1)) Andcrsen on r\;or\vc@m men support and cxstcntl other studies indicating that short-tcwu physical improved muscular ahilit!., acq~~ircd through relatiwl! study, training, also confcw a distinc+ advantagc~ in the cold (2). 1I1 Andmen’s it is of interest that concomitant cold c~sposuredid Ilot improw the to1cwnc.c to cold over that achiwwl 11v training alow. . phvrical . r2lthough man has occupied the Arctic and sub-arctic rc@ms ( and no\v (~VW the =\ntarctic) only through the de\~elopment of tcchnololy and behavioral adaptation, the contrilmtion to his comfort mad(, l)y physiologic adaptations is still of interest and perhaps of some importance. Dr. Prosscr czpresscd the view that the initial rc’sponsc>to stress w;\s often a lxbvioral one, followed Intel implying that the latter IWS more cwnomical or I)!. physiologic adaptation, mow c+Fiicicnt for the organism. 1%‘~ \~oultl like to kno\v the limits of th(s adaptive capacity iillposcY1 on various populations by tlwir gewtic l~ack~ro~iiid and tlw cost of acqiiiring and rc+aining physiologic adaptations. Considering how to invcsti gate these proMcms, it stems impractical to bring poplilations. or good samplrs of populations, to tllck lalwratory for controlled studies and critical csperimcwts. One has only to think of the time>required to stlidy hllman adaptations during the dc\7c,lopnic,ntal pctriotl of an individltal. \1’(, llavcb to search for itatural situations likcl!. to ;uis\~w the qucxtions. Such a sitiiation has Ix~n cwvisioncd lI!- Harrison et r/l. in a plail for idwtifying thr cornponcnts of adaptation to altitude in the Himalayan rcsgions as part of the Tntcrnational Biological Program Human Aclaptahilit\r Proposals (8). Essentially. tll(i plan is a comparison of two populations, one indigenous to high nltitlldes hut kvith rrccnt migration to 10~~altitude , and the other in the opposite situation. It is hoped that similar studies will lw made on Arctic populations: geneticall) similar ones in different ciivironmcnts, and gcnctically dissimilar 0x3 in the same vnvironmcnt. The cwmination of these populations must 1~ intcnsi\zt and include all aspwts of their interaction with the total cknvironment. It will not be sufficient to look merely at gwetic markers and physiologic tests to hwt, to cold, or to low barometric pressurcl. This lesson is clearly pointed out in the report by Edholm et ~1. of the performance of a military task in a hot climate (6). Of three groups of subjects, orw was naturallv acclimatized, once artificially acclimatized, and one nonacclimatized ( control ) . Their abilitv to perform the military tasks in the heat bore little relationship to the physiologic parameters of adaptation to heat, but was probably more clcwly related to such uncontrolled factors as intelligence and motivation. Similarly, in a study specifically designed to assessmotivation in carrying out a particular task in a South African gold mine, Wyndham ef al. (1’7) found that, although physiologic capacity imposed certain limitations on the amount of physical work performed during a work shift, the variability between indi-

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HILDES

viduals and the mean level of work performed were related more to the quality of the supervision than to either of the two physiologic parameters measured, BIOLOCIC

FACTORS

IN

THE

ENVIRONMENT

Two of the biologic factors in the environment to which both physiologic and cultural adaptations may occur are nutrition and infection. Man has successfully adapted to a great variety of foodstuffs and dietary patterns. Also, the amount of food energy available varies between populations and from time to time. It may be stretching a point to label the response to starvation and to chronic undernutrition as adaptive, but there is evidence that the organism reacts to these stresses in a way which promotes survival, and therefore may be considered adaptive in the sense. FVith respect to essential minerals, Mitchell (13) in his review of nutritional adaptations discussed the evidence of the adaptation of adult man to severe restrictions in dietary calcium. He concluded that some individuals have the capacity to adapt to low dietary calcium intake. However, McCance et al. in a recent review of the same topic consicler it still to be an open question ( 11) . One aspect of the relationship between nutrition and cold tolerance that has interested me is the apparent dependence of the elevated basal metabolic rate of Eskimos on the dietary intake of protein. 1Vhen two Caucasian men voluntarily used an exclusively meat diet for a year the\ did not develop a significant increase in basal metabolic rate (13). I wonder if the Eskimo has a genetically dctermincd capacity for metabolizing larger amounts of protein than Europeans. One might look for differcnccs in enzyme systems-in the gut for the absorption of protein, and in the body for metabolizing it. As far as I know there have been no studies of these points. It has been said that infection has been one of the great selective forces in the evolution of man. The special advantages of heterozygosity with respect to sickle-cell trait in malarious areas is the example usually quoted (1). However, little is known of the tolerances developed to specific organisms by various populations. ln an antibody survey carried out in conjunction with my colleagues at the University of Manitoba on Canadian Arctic Eskimos, we were rather surprised to find a remarkably high incidence of antibodies to psittacosis virus (10). At first, WC were skeptical of the significance of these antibodies, but this has now been confirmed in a number of Eskimo and Arctic Indian populations, from different parts of the Canadian Arctic (9). 1%‘e arc not certain whether these antibodies represent the prevalence of a serious disease carrying a high mortality and morbidity which has gone unrecognized, or whether the relationship between the host and the parasite has been altered by some adaptive mechanism so that the virus has diminished virulence for these populations. Positive skin tests for trichinosis are also prevalent in the Arctic, but, since clinical cases of the acute disease with the usual severe features have been reported, this situation may be quite different. CULTURAL

I have mentioned in the environment,

ASPECTS

OF

THE

ENVIRONhlENT

the cultural adaptations which man makes to the stresses but we should also consider the special cultural aspects

ECOLOGIC

AND

ETHNIC

ADAPTATIONS

421

of the environment, These include social organization and attitudes, mating habitual level of physical activity, dietary habits, and inpatterns, crowding, automobiles, air pollution, drugs, clothing, and vttntion and technology. Noise, soap are all parts of WI cultural environment. The habitual use of clothing may have interfered \vith our natural capacity to react to cold in a primitive for physical way; and the automobile may greatly diminish the requirement of [xertion. Hygiene may have greatly influenced not only the epidemiology infectious diseases, but perhaps also our physiologic adaptations to the organisms.

I think we may be confident that man will continue to change his environment at will, and at the same time decrease his adaptive rtquircments for noise, physical fitness, nutritional de& the cstremes of temperature, prcssurc, man is acquiring new adaptive ciencics, etc. A major question is whether capacities fast enough to keep up lvith the changes he is making in his environmcnt; e.g., adaptations to air pollution, ionizin, fl radiation, and crowding. We callnot turn back the clock. Man is continuing to evolve, even though genetic evolution may no longer be the most important mechanism of this progrc,ssivc change. We should no\\. 1~ turning some of our inventive genius away from considering \i-ays to esploit our environment and toward thr major problems of preserving our own health in a rapidly changing world. REFERENCES Protection afforded by sickle-ctxll trait against snl)tertian 1. ALLISON, A. c. (1954). malarial infection. B,rit. Mctl. J. 1, 290-29-1. 2. ANDWSEN, Ii. L. (1966). Metabolic and circulatory aspects of tolerance to cold as affected by physical training. Federation Proc. 25, 1351-1356. 3. BAKER, I’. T. (1965). “International Biological Programme. Multidisciplinary St\lclies of Human Adaptability; Theoretical Justification and Method.” H. A. 60. Special Committee for the International Biological Programme, 7 h4arylebone Road, London, N.\?‘.l. by Ginnrlini, Naples, pages 63-71. 4. DILL,D.B., ADOLPII,E F., ANDWILWR,C.G. eds. (196-1). “Handbook of Physiology,” Sect. 3. Am. Physiol. Sot., Washington, D. C. 5. Douz~x~sss~, T. (1962). “hlankind Evolving. The Evolution of the Human Species.” Yale Univ. Press, New Haven, Connecticut. 6. EDIIOLM, 0. G., Fox, R. H., ADAM, J. hl., AND GOLDSMITH, R. (1963). Comparison of artificial and natural acclimatization. Fcdcrution Proc. ‘22, 709-715. 7. IIM~WZL, I-I. T. (196:?) S ummary of thermal patterns in man. Fedcrutim Proc. 22, 846-S-17. 8. IIARIUSON, G. A., BAKER, I’. T., 4x1 WEINER, J. S. (1966). “Biology of Hnman Adaptability.” p. 509. Clnwndon l’wss, Osford. 9. HILDILS, J. A. ( 1966). A note on psittacosis antibodies in Canadian Eskimos and &&tic Inclians. Itttern. PatJlol. 7, 74-75. IO. IIILDES, J. A., WILT, J. C., :\PI‘I) S-l;\s~le~D, F. J. (1958). Antibodies to adIITCIIFLL, H. H. (1961). In “Nutrition , ,4 Comprehensive Trcatisc” (G. H. Beaton, and E. Jf’. McfJenry, cds. ) Vol. 2. p. 751. Acatlcmic Press, Kcw York.

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1-I. HODAIIL, I<. ( 1962). Basal metabolism of the Eskimo. J. N&r. 15. WEINER, J. S. ( 1963). Discussion. Federation PTOC. 22, 849. 16. WEINEH, J. S. ( 1964). In C. A. Harrison, J. S. Weiner, Barnicot. “Human Biology.” Clarendon Press, Oxford. 17. WYNDHAM, C. E-I., COOKE, H., MUNRO, A., AND MARITZ, J. of physiological factors to the performance of moderately heavy 7. 121-137.

48, 359-368. J. hl. (1961). physical

Tanner, The work.

and

N.

contribution Ergonomics

A.