Chimpanzees help each other on request but not v...(by poking its arm through a hole in the ...)

"Communicative interactions play an important role in altruism in chimpanzees," said Dr Yamamoto. "While humans may help others without being solicited, the chimpanzees rarely voluntarily offered an effective tool to a struggling partner. Indeed, simple observation of another's failed attempts did not elicit voluntary helping in chimpanzees."

Helping upon request may be a more economical and effective strategy. Altruistic behavior by definition produces no direct immediate benefit to the actor; making a request is a clear indicator to the actor that the recipient requires help, minimizing the risk to the actor of unnecessarily behaving altruistically. In this sense, "help upon request" is an ideal strategy since the helping is always helpful and not wasted. This type of altruism may have initially driven the prevalence and development of altruism during human evolution.

One important question for future research is whether high-frequency, voluntary altruism is a behaviour unique to humans. Some new world monkeys have demonstrated unsolicited prosociality suggesting that voluntary altruism evolved in phylogeneticallydiverse taxa but for now, there seems to be no consensus on what is the decisive factorin explaining species differences.

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