Humans have an enormous capacity for generosity. We give money to the homeless in need of shelter and to distant strangers in times of catastrophe. We even give indirectly by donating money to friends and colleagues fundraising for their own charities. But why do we give? And how much are we willing to part with? These were the questions taken up by Nichola Raihani and Sarah Smith in a clever study in a recent issue of Current Biology. The answer is amusingly predictable; in short, it's all about sex.

Each spring, an army of athletes raises money for their favourite charity by completing the London Marathon. After picking a charity, runners solicit everyone they know to pledge money that is paid out following race completion. It's a spectacularly successful scheme, raising some £50 million annually. It also provided Raihani and Smith with a unique opportunity to study patterns of human generosity because donations are online and completely public.

Each donation page has a photo of the runner and then a consecutive list of the money given by each donor. On their own, donors would (probably) contribute different amounts, perhaps varying according to their financial circumstances or their relationship to the runner. However, this set-up is highly context dependent: donors know the recipients and, crucially, they can also see what the previous person gave. And it turns out this context matters a great deal.

When following an ‘average’ donor, individuals in turn contribute the average amount. However, when the previous donor gave an especially large donation, this triggered a response known as ‘competitive helping’, a form of one-upmanship that results in the second donor out-giving the first. Crucially, however, competitive helping was sex specific. While donations from females were unaffected by the sex of earlier donors, men gave more if the previous large donor was a male. More interesting is that the extent of competitive helping among men was entirely dependent on the attractiveness of the runner herself. In practical terms, this amounted to about £30 more per donation. In short, the researchers found that men compete with each other for the perceived recognition of attractive female fundraisers, and the manner in which this is done is by flaunting cash.

Humans, of course, are not alone in using social cues to adjust their behaviour. Males vying for access to females use all manner of exaggerated displays to convince potential mates of their suitability, and the extent of their signalling increases with an audience. The present study clarifies that, for humans, males work harder to beat each other when their perceived ‘mate’ is a more attractive catch. At the same time, the men are using fairly honest signals of their own quality. Not only do the men in these fundraising games provide direct evidence of their wealth, a quality that is difficult to fake, but they also hint at their generous, good-hearted tendencies. And who doesn't want this in a mate?

But what is generosity anyway? Is it entirely selfless, and is it any less so if it is tainted with cryptically selfish and largely unconscious motivations? The work of Raihani and Smith cannot answer this. However, one can envisage the exciting follow-ups to this study that seek to identify the consequences for these competitive helpers. In the end, do they get the girl? Do the fundraisers run straight from the marathon into the arms of their donors? Probably not – but we'll have to wait until the sponsorships from the next London Marathon are in to find out!

N. J.
Competitive helping in online giving
Curr. Biol.