Discussion

Involvement in fights

Since the proportion of left-handers is greater in populations with higher homicide rates (Faurie and Raymond, 2005), it has been questioned whether left-handers could have a more aggressive behavior. However, in the present data, no significant effect of handedness was found on the probability of ever having fought, which supports the hypothesis of no innate difference between right- and left-handers. These results thus support the hypothesis that previous successful experiences lead to an increase in fighting behavior, since a greater involvement of left-handers in fighting interactions was found among men who had fought at least once during their lifetime. The causal relations involved in the association between handedness and fighting behavior are not yet known. We hypothesize that left-handers tend to fight more often because of the psychological consequences of their increased chances to win a fight, due to their frequency-dependent advantage in fighting. Such a strategic advantage in previous fighting experiences could indeed improve their self-confidence. Only about a third of our sample noticed that handedness could influence the probability of winning a fight, but among them, a large proportion considered left-handers as advantaged, and this proportion was even higher among left-handers. Moreover, success in past experiences may increase left-handers' self-confidence, even without being conscious of their advantage being due to left-handedness. Hence the self-confidence of left-handers may increase throughout their lifetime and make them prone to fight more often. If winning a fight increases the probability to engage in future fights, then one can expect that more left-handers than right-handers will engage in more than one fight, due to the well described fighting advantage of lefties. Concerning the first fight in life, statistical analyses don't reveal any difference between left- and right-handers. This could either be due to a lack of power, an insufficient sample size, or to the fact that there really is no difference. An absence of difference is, however, not incompatible with the fighting hypothesis. It may not be possible to adopt a fighting strategy in order to take advantage of fighting superiority before being aware (consciously or not) of this superiority.

The information on who started the fight and who won would allow better testing of this hypothesis. Obviously, if left-handers take part in more fights but lose the majority of their fights, then this would not be in support of the fighting hypothesis. Such measures need to be incorporated in further research. Whatever the psychological and biological basis of such behavioral differences, the greater involvement of left-handers in fights may improve their success in male-male competition.

Health status and age exhibit no significant association with the probability of ever fighting and with the frequency of fights, whereas the socio-economic status does. Weight (and height, to a lesser extent) was associated in this sample with the probability of ever fighting and with the frequency of fights. Heavier men seemed more prone to fighting. Weight could indeed confer a greater probability of winning, and successful past experiences might have similarly improved the heavier men's self-confidence and increased their desire to fight.

Note that participants might have interpreted the term “physical fight” differently: some might include pushing or grabbing, whereas others might only consider punching, beating or kicking as real physical fighting. Such variability would, however, not challenge our results, provided that the definition of fights is not systematically biased according to hand preference. The estimation of the number of fights by self-reports might be distorted by memory bias or deceptive response. However, fighting events are probably less subject to oblivion than more common or daily events, although this has not been formally measured. In addition, data have been categorized, thus reducing the effects of a possible memory bias. Direct behavioral observations of both fighting behavior and hand preference would allow further testing of our hypothesis.

Another bias is possible, due to a response bias: Although our questionnaire was sent to 50% of right- and 50% of left-handers, our final sample comprises only 40% of left-handers. If non-respondents have fought significantly less than respondents, there is potentially a bias.