In Brazil, indigenous societies' "first contact" with European colonization has typically brought collapse, but they have shown the ability to rebound in some cases, researchers say.
When Europeans began arriving in the region that is today's Brazil, the result was the loss of 95 percent of indigenous populations and most of its existing tribes, they say.
A study of the country's indigenous societies by researchers at the Santa Fe Institute in New Mexico suggests that despite that grim history, there is reason to be hopeful about the preservation of some of them, although it can't be taken for granted.
Even in outside contact with indigenous societies occurring in the last five decades, "all of them went through a collapse, and for the majority of them it was disastrous," researcher Marcus Hamilton says.
Violence and disease are responsible in the majority of cases, he says, with ongoing detrimental effects for the societies.
"That's going on today -- right now," he says.
Hundreds of indigenous tribes that have experienced contact with outsiders are still in Brazil in what Hamilton calls "a tragic natural experiment."
The Brazilian non-governmental Instituto Socioambiental has gathered census data about more than 200 indigenous societies for more than a half-century.
That data has allowed survival prospects and health of both the remaining contacted and the uncontacted indigenous societies to be analyzed in detail, Hamilton says, something not possible in any other part of the world.
Even though first contacts resulted in average population declines of around 43 percent, those declines bottomed out eight to nine years after the initial contact, after which they increased by around four percent annually, about the maximum possible, he says.
The data suggests both contacted populations and those that have not yet experienced outside contact could recover from a population of as little as 100 individuals, he says.
Despite that hopeful prognosis, the researchers wrote in the journal Scientific Reports, other factors will still threaten such societies, including a breakdown of tribal interactions, deforestation and assimilation with outside society.
Economics, politics and ongoing illegal exploitation of tribal lands also represent a threat, the researchers say.
"Demographically they're healthy," Hamilton says, but their survival in the long term is "very up in the air."
