Is our species strongly motivated by egalitarian thinking/instincts?

There's an interesting piece in an April 2007 issue of NATURE (doi:10.1038/nature05651). I excerpt the gist of it. The researchers conducted an experiment designed to test whether humans follow egalitarian strategies even when they are not forced to do so (ie they could, anonymously, be completely selfish and aim for the maximisation of their own benefits). Interestingly, in the experiment, those well-off transferred anonymously some of their wealth to the least well-off while those least well-off also aimed to reduce inequality. There was some concern about free-riders, but the basic principle driving the research participants (independent of each other, anonymously, and without any coercion) was egalitarian in nature. Anyway, here's some content from the paper:

'The results show that subjects reduce and augment others’ incomes, at a personal cost, even when there is no cooperative behaviour to be reinforced. Furthermore, the size and frequency of income alterations are strongly influenced by inequality. Emotions towards top earners become increasingly negative as inequality increases, and those who express these emotions spend more to reduce above-average earners’ incomes and to increase below-average earners’ incomes. The results suggest that egalitarian motives affect income-altering behaviours, and may therefore be an important factor underlying the evolution of strong reciprocity and, hence, cooperation in humans.
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To elicit emotional reactions, we presented subjects hypothetical scenarios in which they encountered group members who obtained higher payoffs than they did (see Methods). Subjects were then asked to indicate on a seven-point scale whether they felt annoyed or angry (1, ‘not at all’; 7, ‘very’) by the other individual. In the high inequality’ scenario, subjects were told they encountered an individual whose payoff was considerably greater than their own. This scenario generated much annoyance: 75% of the subjects claimed to be at least somewhat annoyed, whereas 41% indicated a high level (4 or more) of annoyance. Many subjects (52%) also indicated that they felt at least some anger towards the top earner. In the ‘low-inequality’ scenario, differences between subjects’ incomes was smaller, and there was significantly less anger (Wilcoxon signed rank test, P, 0.0001) and annoyance (P,0.0001). Only 46% indicated they were annoyed and 27% indicated they were angry. Individuals apparently feel negative emotions towards high earners and the intensity of these emotions increases with income inequality.
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These emotions seem to influence behaviour. Subjects who said they were at least somewhat annoyed or angry at the top earner in the high-inequality scenario spent 26% more to reduce above-average earners’ incomes than subjects who said they were not annoyed or angry. These subjects also spent 70% more to increase below-average earners’ incomes. Mann–Whitney tests of both differences indicate that they are significant (one-tailed, P50.05 and P50.001, respectively).
Emotional reactions towards high earners—even when the source of income is known to be purely random—cause individuals to engage in costly acts that promote equitable resource distributions. The evidence here indicates that social inequality arouses negative emotions that motivate both the reduction and augmentation of others’ incomes. This finding supports research that indicates humans are strongly influenced by egalitarian preferences.
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Finally, the results are also consistent with the punishment of noncontributors and the reward of contributors in public good games. Although concerns for equality are clearly not the only motive for human behaviour in these contexts, our results suggest that egalitarian motives may underlie strong reciprocity and, thus, play an important role in the maintenance of ooperation.

Part of the problem I have with this experiment is that it cannot control for ownership in the sense that the redistribution that took place in this experiment took place among people who didn't know each other, and where those that provided some of their wealth voluntarily to support those less well-off did not actually really spent any of their own wealth, but merely hypothetical wealth in an experimental situation.