Scientists used to think chimpanzees - our close relatives - were a gentle, peace-loving species, until they observed their behaviour in the wild and found they could be quite murderous in the treatment of other chimps.
And what was it that caused them to become so vicious? The arrival of chimps from a different troop in the part of the forest they considered to be their territory.
I remembered this one day after failing to persuade a friend who took a dim view of boat people that her objections were unfounded. Whenever I knocked down one argument she'd just switch to another.
Our evolutionary history has left us with an instinctive fear of outsiders - people who are different, people who invade our territory to steal our food and our women or, in the contemporary context, to jump the queue and steal our jobs, overcrowd our schools (and win most of the prizes), overwhelm our culture, crowd out the rellos we're trying to get into the country, push up house prices and add to congestion on the roads.
You can call it racism or religious intolerance - the nation that invented the White Australia Policy can hardly object to that charge, except to say we're no worse than most nationalities and better than some.
But it's best thought of as xenophobia - a fear of foreigners, people who are different, who aren't one of us.
And it's so deeply ingrained in us - so visceral - it's not susceptible to rational argument. It would be nice if a greater effort by the media to expose the many myths surrounding attitudes towards asylum seekers could dispel the fear and resentment, but it would make little difference.
Our politicians have long understood that widespread dislike of newcomers, especially those of darker skin or strange religious practices, lay just beneath the surface and could be easily aroused. The politician or party that tapped this vein would draw much support.
For decades there was an unspoken agreement between the major parties to keep such tactics off limits. Their role was to avoid bringing out the worst in the Australian psyche.
But maybe 20 years ago that bipartisan approach began breaking down. Perhaps it was the rise of Asian immigration, perhaps the era of so many people arriving uninvited by boat.
It may be true we have a bigger problem with visitors arriving by plane and overstaying visas, but the more visible arrival of scruffy people on an overcrowded, leaky boat - the footage of which can be replayed many times, leaving an exaggerated impression of the numbers involved - seems far more threatening.
Perhaps it was the huge rise in the levels of sanctioned immigration in recent years, for which governments have failed to provide sufficient housing and public infrastructure.
Another factor was the advent of talkback radio, which gave greater currency to the disaffection of individuals, and then the rise of shock jocks who, in pursuit of ratings and commercial gain, where prepared to incite their listeners' resentments.
Pauline Hanson brought the issue crashing onto the stage of federal politics, forcing the major parties to respond. But politicians had begun walking away from their commitment to avoid politicising the issue much earlier.
Perhaps they couldn't avoid responding to public concerns; perhaps in the heightened contest between the parties they could no longer resist the temptation to gain an advantage over their opponents.
Some people blame it all on John Howard, but the harsh treatment of boat people began under his Labor predecessors. And whoever started it, once the embargo had been breached both sides got down and dirty.
Julia Gillard took the debate to a lower level before the election when she invited people to give their prejudices free rein. "People should feel free to say what they feel," she said. "For people to say they're anxious about border security doesn't make them intolerant. It certainly doesn't make them a racist."
To acknowledge we have an evolutionary predisposition to fear and resent outsiders is not to condone such attitudes. The process of civilisation involves gaining mastery over our base emotions which, if they once contributed to our biological "fitness", are now antisocial and counter-productive.
But if such attitudes are instinctive and impervious to rational argument, what's to be done now the pollies have let their standards fall?
I was at a loss to answer that until last week and the arrival in Sydney of that poor distressed orphan boy for the funeral of his father. Suddenly a crack appeared in the wall of prejudice against boat people. Tony Abbott and his immigration spokesman, Scott Morrison, got caught going beyond the pale in their pursuit of electoral advantage. It emerged that Morrison had earlier proposed exploiting the popular resentment of Muslims, but had been rebuffed by colleagues insisting the Liberals' long-standing commitment to a non-discriminatory immigration policy remain inviolate.
The minister, Chris Bowen, was widely criticised for his bureaucratic and insensitive treatment of the boy and his relatives. And it seems the episode has prompted Gillard to find the courage to lead.
"People easily fear change. People easily fear difference," she said. "It is the job of national leadership to reassure in the face of that fear, to explain to people that there is ultimately nothing to be afraid of."
What changed? Here's a clue: in their efforts to gratify and exploit public resentment of "illegals", governments of both colours have given the highest priority to preventing individual boat people from telling their stories to the media. They must continue to be seen as monstrous invaders, never as flesh and blood.
Our attitudes towards asylum seekers may be impervious to rational argument, but they're not to rival emotions - particularly the positive emotion of empathy.
Like all nationalities, Australians are neither good nor bad, they're both. Our leaders can play up to our darker side, or appeal to the better angels of our nature.
