"Therefore, most of the time, banishment did not lead to starvation or even necessarily isolation."
Do you have a reference for that? It doesn't jibe with my understanding of banishment, but my readings are from agricultural traditions. More specifically, outlawry under Germanic law, where someone was judge to be outside of the protection of the law. Full outlawry on Iceland effectively meant banishment from Iceland or death. (See https://www.nottingham.ac.uk/english/documents/innervate/09-... .)
I found https://books.google.com/books?id=9ZkIAAAAQBAJ&lpg=PA81&ots=... which says:
> By the end of the last ice age .... To be cast out of a band .. usually meant total banishment from the society and eventual death, either by starvation or as a result of aggression by members of another society (Salisbury, 1962).
And here's a reference concerning Aboriginal use of banishment, from http://www.ajic.mb.ca/volumel/chapter2.html :
> As in European societies, some crimes required the complete removal of the criminal from society. In most Aboriginal societies, this meant banishment. In such close, family-oriented societies, where survival depended upon communal cooperation, such sanctions were considered a humane alternative to death, no matter how traumatic they may have been to the offender.
Further, http://rsc2012hscls.wikispaces.com/file/view/Law+Reform+Coun... :
> Exile or banishment has been described as an extremely harsh punishment and was not embraced by all Aboriginal societies.
This does not sound compatible with your conjecture that pre-agricultural era banishment was not a real threat.
Further, I do not follow the logic to "Therefore, most of the time, banishment did not lead to starvation".
Consider this non-real scenario. Humans can survive only be eating buffalo meat. There are huge numbers of buffalo compared to humans, so there is a food surplus. However, it takes 10 people to kill one buffalo. In that scenario, exiling someone leads to certain death as a lone human cannot hunt a buffalo. While the human species is not resource-constrained, a single human is.
Similarly, in Intuit cultures there were strong specializations between male and female roles. For example, it was women who were trained in how to sew the skins to make clothes against the harsh weather, while the men learned hunting skills. If a male were banished, I wonder if he might not have the skills to survive on his own.