This an interesting proxy. It should shadow the complexity of social structure. In biology, altruism is defined as a behaviour by an individual that increases the fitness of another individual, and decreases their own. This poses a bit of a problem, and let me explain why.
If you are a rabbit, then your main competitor is not the fox, its other rabbits. You don’t need to be able to outrun a fox for your genes to be highly favoured, simply being faster than other rabbits will do almost as well. In altruism your genes are directing you the opposite way. A clue as to why that could happen comes from one of its most common, and extreme, forms: child rearing. You are usually far more closely related to your children than another member of your species selected at random. By nurturing them you are preferentially nurturing your own child rearing genes. This sort is called kinship altruism.
However, there is a known way around every rule. Altruistic behaviour can develop in outbreed groups under a system called ‘reciprocal altruism’. Reciprical altruism entails identifying a large number of individuals, having a long memory of them, being able to tally up favours given and received, and holding grudges. All four elements need to be in place or the system will collapse due to cheaters, so this needs complex social environment. Another requirement is that each given favour is fairly small in itself, and that no debt to any one individual gets too large that it can’t reasonably be expected to be repaid.
An animal would only need the minimum intelligence of a vampire bat (clever but not startling) to employ reciprical altruism. Even this, however, is inadequate here, as helping to raise young is just too big a favour, to be facilitated by this mechanism.
Like wolves, the whole sperm whale unit helps raise a new born calf. Unlike wolves, and unlike any other cetacean, sperm whales are not purely suckled by their mothers, but can be by any adult female. That is half of the problem, the other half is, that these unit members are often not even related to each other. This is extreme and persistent altruism, but our two main mechanisms for explaining how it can arise in the face of evolution fail miserably here.
I would like to hear from any biologist who know of anything remotely similar in the animal kingdom. For my part, the closest I can find is in some human populations but, even then, I have never heard of it reaching the extent seen here. I would be thankful to any anthropologist that might know of an example.
I suspect that only very rapid information exchange (faster than those mediated by genetic change over evolutionary timescales), and the ability to make complex, cross generational ‘contracts’ can explain the behaviour observed in sperm whales.