There are large variations of size among humans but in all populations, men are larger on average than women. For most biologists this fact can be easily explained by the same processes that explain the size dimorphism in large mammals in general and in apes in particular. Due to fights between males for the possession of females, sexual selection has favoured bigger males. Indeed, this factor certainly explains why males are selected for being large but lets aside the question of selection on the female side. Actually, it has been shown that larger females are also favoured by natural selection. This is particularly relevant for women because their probability of dying when giving birth is then reduced. In this paper, the common view that size dimorphism in humans results from the fact that the advantage of being big is stronger for men than for women is challenged by another hypothesis, namely that the difference results from a difference of cost rather than from a difference of benefits. The cost of being big would be higher in women simply because, under gender hierarchical regimes found in all cultures, men are allocated the best food. The interaction between evolutionary forces and cultural practices could then lead to this disadaptive situation

Pierre-Henri Gouyon

Priscille Touraille

English

Nature Precedings

1 
Why are women smaller than men? When anthropology 
meets evolutionary biology 
Priscille Touraille1 & Pierre-Henri Gouyon2 
1Musée de l'Homme Unité Eco-anthropologie (UMR 5145 CNRS-MNHN-P7), Muséum 
National d’Histoire Naturelle de Paris, 17 place du Trocadéro, F-75116 Paris. 
2 OSEB (UMR 5202 CNRS-MNHN) Muséum National d’Histoire Naturelle de Paris, 12 
rue Buffon F-75005 Paris. 
There are large variations of size among humans but in all populations, men are 
larger on average than women. For most biologists this fact can be easily explained 
by the same processes that explain the size dimorphism in large mammals in 
general and in apes in particular. Due to fights between males for the possession of 
females, sexual selection has favoured bigger males1,2,3. Indeed, this factor certainly 
explains why males are selected for being large but lets aside the question of 
selection on the female side. Actually, it has been shown that larger females are 
also favoured by natural selection. This is particularly relevant for women because 
their probability of dying when giving birth is then reduced4,5,6. In this paper, the 
common view that size dimorphism in humans results from the fact that the 
advantage of being big is stronger for men than for women is challenged by 
another hypothesis, namely that the difference results from a difference of cost 
rather than from a difference of benefits. The cost of being big would be higher in 
women simply because, under gender hierarchical regimes found in all cultures, 
men are allocated the best food. The interaction between evolutionary forces and 
cultural practices could then lead to this disadaptive situation. 
Being large is undoubtedly advantageous for men but also for women. Concerning 
men, the advantage is usually supposed to involve survival and/or reproductive output 
2 
(through competition between men, whatever the form it takes)1,2,3. Concerning women, 
an important component is the fact that the probability of death of both the mother and 
the child decrease with the size of the mother4,5,6. The fact that there seems to exist a 
stable body size while there is heritable variation for this trait indicates that the 
advantage stated above is compensated for by a cost. This cost is probably at least partly 
due to the fact that increasing the body size involves a higher resource acquisition but 
can also involve different kinds of scaling effects like the surface/volume ratio which 
decreases as the size increases. The expected individual size should be determined by 
the point where the cost and benefit curves cross. This point is stable if the benefit is 
lower than the cost when the size is below this point and reciprocally (Fig. 1.). 
The existence of a dimorphism indicates that at least one of these two curves 
(benefit or cost) is different according to the sex of the individual, or at least has been 
different in the past. Indeed, such a dimorphism is found in all human populations7. One 
could imagine that this dimorphism is simply a remnant of an old one, which existed at 
the time of our common ancestor with say Gorillas8,9. However, this hypothesis can be 
rejected because (i) the degree of dimorphism is variable among populations and 
families10,11 and (ii) this variation is heritable12. Given these facts, the present situation 
cannot be simply the perpetuation of the preceding one. Selection should be able to 
shape efficiently the size dimorphism in humans6,13,14. 
The classic explanation favoured by biologists is that dimorphism results from a 
difference between males and females in terms of benefit of being large. Fig. 2. shows 
such a case. Indeed, an increased size is beneficial in terms of fitness both to males and 
females. But the increase of fitness being higher for males than for females, a similar 
cost for both sexes leads to an “equilibrium” situation where males are bigger than 
females. This explanation certainly holds for a lot of big mammals, including apes 
because individual fights remain an important factor in the determination of social status 
3 
and access to females concerning the males15,16,17. This explanation has thus been 
critically discussed for different classes and orders of animals18,19 and particularly for 
the primates order20, 21,22,23,24. 
In humans, it is likely that this very factor has long been less important than in 
other species. Indeed, numerous authors have stated that other environmental factors are 
involved, nutrition being one of them14,25. Anthropological data about the non 
egalitarian access to resources that characterizes human societies could explain the same 
fact. This suggests that we should start thinking in terms of differences in costs rather 
than in terms of benefits. It has been shown that in almost all known populations 
worldwide, restrictions are very often targeted at the critical period of a woman’s 
reproductive lifetime26, and women as a group are supposed to get less food in terms of 
quantity and of quality than men do25,27. This reality is expected to be the direct 
consequence of an institutionalized inequality in favour of men that the social sciences 
have named the gender order28. Even if the benefit of being big is as great for women as 
it is for men, and even if there is not any advantage in being big for men anymore, this 
difference of resource allocation would generate a difference in cost which can explain 
the size dimorphism (see Fig. 3.). This hypothesis holds for humans and perhaps for 
some primates where females have no priority for access to resources29, contrary to 
what happens for some monomorphic primates30. 
It is thus suggested that, in humans, the differential cost associated with growth in 
males and females is different, thanks to the unequal sharing of resource between males 
and females. This would generate a dimorphism even in the absence of differences of 
benefits associated with increased size between the sexes. In order to test this hypothesis 
against the “standard” model, one would need to determine the curves of cost and 
benefits for males and females in different conditions. A precise knowledge of these 
curves would certainly be difficult to reach but it is probably possible to find orders of 
4 
magnitude of variation. Note that the two hypotheses are not exclusive and if they are 
both true, the effect will be even greater. It is interesting to notice that in our hypothesis, 
the fact that females are smaller than males is far from being optimal. Given that the 
reproduction is physiologically realized by women, there would have been incredibly 
less child and mother damage in human history if females have had access to a richer 
diet: the cost of growing more would be decreased and they would reach a size which 
allows them to give birth with a decreased probability of accident and depletion. 
Furthermore, from a demographic point of view, this situation would be more 
favourable for the population. There has always been in the literature a strong tendency 
to interpret cultural affairs in terms of biological success. Such biological arguments 
have long been used to justify unfair social rules. The present case could constitute a 
counter-example where a cultural trait is counter-adaptive because of its evolutionary 
implications. 
  
 
1. Darwin, Ch. The Descent of Man, and selection in relation to sex. (J. Murray, 
London, 1871). 
2. Alexander, R. D., Hoogland, J. L., Howard, R. D., Noonan, K. M. & Sherman, 
P. W. Sexual dimorphisms and breeding systems in pinnipeds, ungulates, 
primates, and humans in Evolutionary biology and human social behavior: an 
anthropological perspective (eds Chagnon, N. & Irons, W.) 402-435 (Duxbury 
Press, North Scituate, Mass., 1979). 
3. Pawlowski, B., Dunbar, R. I. M., Lipowicz, A. Evolutionary fitness: tall men 
have more reproductive success. Nature, 403, p.156 (2000). 
5 
4. Martorell, R., Delgado, H. L., Valverde, V., & Klein, R. E. Maternal stature, 
fertility and infant mortality. Human Biology, 53 (3), 303-312 (1981). 
5. Sear, R., Allal, N., & Mace, R. Height, marriage and reproductive success in 
Gambian women. Research in Economic Anthropology, 23, 203-224 (2004). 
6. Guégan, J.-F., Teriokhin, A. T. & Thomas, F. Human fertility variation, size-
related obstetrical performance and the evolution of sexual stature dimorphism. 
Proceedings of the Royal Society of London. B., 267, 2529-2535 (2000). 
7. Eveleth, P. B. Differences between ethnic groups in sex dimorphism of adult 
height. Annals of Human Biology, 2 (1), 35-39 (1975). 
8. Leutenegger, W. & Cheverud, J. M. Sexual dimorphism in primates: the effect 
of size in Size and scaling in primate biology (ed Jungers, W. L.) 33-50 (Plenum 
Press, New York/London,1985) 
9. Gaulin, S. & Boster, J. Cross-cultural differences in sexual dimorphism. Is there 
any variance to be explained ? Ethology and Sociobiology, 66, 495-507 (1985). 
10. Shea, B. T. Ontogenetic approaches to sexual dimorphism in Anthropoids. 
Human Evolution, 1, 97-110 (1986). 
11. Oxnard, C. E. Fossils, teeth and sex. New perspectives on human evolution. 
(Hong Kong Univ. Press, Hong Kong, 1987) 
12. Badyaev, A. V. Growing apart : an ontogenetic perspective on the evolution of 
sexual size dimorphism. Trends in Ecology & Evolution, 17 (8), 369-378 (2002). 
13. Gaulin, S. J. C. & Boster, J. S. Human marriage systems and sexual dimorphism 
in stature. American Journal of Physical Anthropology, 89, 467-475 (1992). 
6 
14. Wolfe, L. D. & Gray, P. J. A cross-cultural investigation into the sexual 
dimorphism of stature in Sexual dimorphism in Homo sapiens. A question of size 
(ed Hall, R. L.) 197-230 (Praeger, New York,1982). 
15. Le Boeuf, B. J. & Reiter, J. Lifetime reproductive success in Northern Elephant 
Seals in Reproductive success. Studies of individual variation in contrasting 
breeding systems. (ed Clutton-Brock, T. H.) 344-362 (Chicago Univ. Press, 
Chicago, 1988) 
16. Clutton-Brock, T. H., Albon, S. D. & Guiness, F. E. Reproductive success in 
male and female red deer in Reproductive success. Studies of individual 
variation in contrasting breeding systems. (ed Clutton-Brock, T. H.) 325-343 
(Chicago Univ. Press, Chicago, 1988) 
17. Lindenfors, P. & Tullberg, B. S. Phylogenetic analyses of primate size 
evolution : the consequences of sexual selection. Biological Journal of the 
Linnean Society, 64 (4), 413-447 (1998). 
18. Ralls, K. Mammals in which females are larger than males. The Quarterly 
Review of Biology, 51, 245-276 (1976). 
19. Karubian, J. & Swaddle, J. P. Selection on females can create ‘larger males’. 
Proceedings of the Royal Society of London, B, 268, 725-728 (2001). 
20. Clutton-Brock, T. H. Size, sexual dimorphism, and polygyny in primates in Size 
and scaling in primate biology (ed Jungers, W. L.) 51-60 (Plenum Press, New 
York/London, 1985). 
21. Pickford, M. On the origins of body size dimorphism in primates. Human 
Evolution, 1 (1), 77-90 (1986). 
7 
22. Martin, R. D., Willner, L. A. & Dettling, A. The evolution of sexual size 
dimorphism in primates in The Differences between the sexes. (eds Short, R. V. 
& Balaban, E.) 159-200 (Cambridge Univ. Press, Cambridge, 1994). 
23. Plavcan, M. J. Sexual dimorphism in primate evolution. Yearbook of Physical 
Anthropology, 44, 25-53 (2001). 
24. Kappeler, P. M. Sexual selection in primates: new and comparatives 
perspectives. Evolutionary Anthropology, 11, 173-175 (2002).  
25. White, N. Sex differences in australian aboriginal subsistence: possible 
implications for the biology of hunters-gatherers in Human sexual dimorphism. 
(eds Ghesquiere, J., Martin, R. D. & Newcombe, F.) 323-361 (Taylor & Francis 
Ltd, London,1985) 
26. Spielmann, K. A. A review: dietary restrictions on hunter-gatherer women and 
the implications for fertility and infant mortality. Human Ecology, 17 (3), 321-
345 (1989). 
27. Stanford, C. B. The hunting apes. Meat eating and the origin of human 
behavior. Princeton Univ. Press, Princeton, N. J. (1999). 
28. Connell, R. W. Gender and power. Society, the person and sexual politics. 
Stanford Univ. Press, Stanford (1987). 
29. Jolly, A. The puzzle of female feeding priority in Female primates: studies by 
women primatologists. (ed Small, M. F.) 197-215 (Alan R. Liss, New York, 
1984) 
8 
30. Pollock, J. I. The ecology and sociology of feeding in Indri indri in Primate 
ecology : studies of feeding and ranging behaviours in lemurs, monkeys, and 
apes. (ed  Clutton-Brock, T. H.) 38-69 (Academic Press, London, 1977). 
 
Acknowledgements: the authors are grateful to Françoise Héritier who supervised the PhD thesis of 
Priscille Touraille (from which the main idea of this paper is coming from) and attracted Pierre-Henri 
Gouyon to this subject. 
Correspondence should be addressed to touraille@mnhn.fr or gouyon@mnhn.fr   
9 
Fig. 1. The evolutionary stable size of an individual is determined by the point at 
which the cost becomes higher than the benefit. 
Fig. 2. The classical interpretation of size dimorphism in mammals involves a 
difference of benefit according to the sex of the individual. Although both sexes 
benefit from a larger size, the advantage is higher for males than for females. 
Fig. 3. The proposed hypothesis is that, due to unequal sharing of resources 
between males and females, the cost of a large body size is higher for females; 
this leads to a size dimorphism even if the benefits provided by a larger size are 
equal for males and females or if the benefit for males is lower than for females. 
 
10 
 Fig. 1. 
 
 
  
 
 
 
 
Fig2.    
   
 
 
 
 
 
 
 
Fig 3. 
   





Why are women smaller than men? When anthropology meets evolutionary biology

http://precedings.nature.com/documents/1832/version/1

Why are women smaller than men? When anthropology meets evolutionary biology

Abstract

Similar works

Full text

Available Versions

Nature Precedings