One size does not fit all

Decisions about the height of the person you marry are irrelevant in some cultures

The 'cardinal rule of dating', social psychologists tell us, is that the man should be taller than the woman. Furthermore, tall men have the evolutionary advantage over short men as they are more likely to marry and have multiple marriages. But pity the tall woman, as she might find herself disadvantaged by her height when it comes to finding a marriage partner.

Claims such as these are backed up by a wealth of research on human mating behaviour. It has been demonstrated time and again that size matters when it comes to choosing a partner and facts such as taller, larger men tend to marry taller, larger women are often used to support the argument that assortative mating – partnering with someone of similar characteristics to oneself – according to height and weight arises from evolutionarily adaptive preferences for partners of a particular size

Size therefore clearly matters when it comes to matters of the heart. Or does it? In fact, although there is a large body of research on human mating patterns, studies have so far focused almost entirely on post-industrial societies. Much less is known about the relationship choices of more traditional societies and whether partnerships in these societies follow the same patterns or not.

Dr Rebecca Sear, Senior Lecturer in Population Studies at LSE's Department of Social Policy, believes that without a fuller body of research, academia is in danger of taking too narrow an approach to evolutionary studies of human behaviour. Together with Professor Frank Marlowe of Florida State University she has been examining the mating practices of a small ethnic group in Tanzania and their findings reveal that this traditional, forager society places a significantly different value on size than Western societies when it comes to choosing a marriage partner.

Hazda peopleA small group numbering about 1,000, the Hadza are a hunter-gathers who live in mobile camps averaging 30 people. They marry young: women at around 17-18 and men marrying around age 20. Serial monogamy is the best way to characterise the marriage system – marriage is universal, but both men and women may divorce and remarry, and polygamy is rare (though is permitted).

'Marriage is not arranged and female choice seems to be the main factor leading to marriage, because young single men appear willing to marry a wide range of women' says Dr Sear. 'Previous research suggests the Hadza's mate preferences resemble that of Western mate preferences in some ways but not others. For example Hadza men seem to place much more emphasis on women being hard-working and fecund than Western males.'

Neither preferences nor choices for size have previously been tested in forager populations, so the researchers carried out multiple statistical tests in order to determine whether size and strength do play a factor in the Hadza's marriage choices. 'By examining the size and strength of these couples, we hoped to see whether a traditional hunter-gatherer society would match post-industrialist societies or not' explains Dr Sear.

In order to identify if there was any evidence for assortative mating according to size, the researchers assessed height, weight, BMI and percent fat for each couple. Handgrip strength was also taken as an indicator of overall strength and work capacity. They also examined whether a male-taller norm – another preference for Western married couples - could be found within Hadza marriages. Finally, they assessed whether there was an association between size or strength and the total number of marriages contracted for individuals of each sex.

The results were clear: the Hadza were not considering size when choosing marriage partners. 'We found no evidence that the Hadza were practicing assortative mating according to size, in contrast to Western populations that do record a higher percentage of similar sized partners than if choices were being made with no consideration to height or weight.' explains Rebecca Sear.

'We also found no evidence of a male-taller norm in Hadza society which again contrasts to relationships in post-industrial societies. Western populations like the UK are shown to favour partnerships where the man is taller than the women, leading to the proportion of female-taller marriages being significantly lower than they would number if height was of no concern when choosing a mate. In contrast the number of female-taller marriages within the traditional Hadza population is no different from that expected from mating which is random with respect to height – about nine per cent.'

Size also didn't seem to affect the number of marriages for either sex, again unlike the industrial populations. In the UK, for example, height seems to be an advantage for men but might perhaps be a disadvantage for women. In the Hadza, neither height, nor any other size or strength variable, was correlated with the number of marriages contracted.

'Strength may be more of a significant characteristic' continues Dr Sear, 'and it is possible that where both men and women prefer strong partners, assortative mating comes into play, with the most attractive (strongest) man mating with the most attractive (strongest) female. But our research showed this association was fairly weak and our findings indicate that, as with size, the Hadza do not give strength much consideration when choosing a mate.'

These results are significant as Dr Sear explains: 'Size is usually assumed to be an indicator of health, productivity and overall quality, so this lack of size-related mating patterns might appear surprising. We need to reassess our "bigger is better" view of size, however, since size may not always indicate good health and productivity in all environments.

'Health and productivity may be signalled in alternative ways for the Hadza. An individual's health history may be more important than their size, for example, and this may be relatively well known in a small mobile population. Additionally, there may be some disadvantages to large size in food-limited societies, where costs of maintaining a large size during food shortages may be high. In post-industrialised populations, this wouldn't be a factor, and so size preferences become more of an indicator of quality.'

When it comes to choosing a partner, therefore, it seems that there are striking differences between this hunter-gatherer society and post-industrialised populations. 'Clearly mating choices are not identical across all populations and efforts should be made to test the universality of both preferences and choices before speculation is made on their evolutionary implications' concludes Dr Sear. 'It is time to expand our horizon to a truly cross-cultural view and begin to sort between highly variable and truly universal mate patterns.'


Useful links

How universal are human mate choices? Size doesn't matter when Hadza foragers are choosing a mate |by Rebecca Sear, LSE, and Frank W Marlowe, Florida State University, was published in The Royal Society journal Biology Letters.