It was rush hour in Singapore and my taxi was crawling its way through snarled traffic along Orchard Road. The driver, in the time-honoured tradition of cabbies the world over, was keen to strike up a conversation.
He asked me where I was from and I told him I lived in Sydney.
'How many people are there in Australia?' I told him the population was about 19 million. He jerked his head round, clearly astonished.
'So few people in such a big country? There should be 80 million,' he said.
It is not an unreasonable observation. Australia is huge - the only country in the world that occupies an entire continent. Overlay a map of Australia on a map of Europe and it stretches from Scotland to Turkey, from Norway to North Africa.
Surely it can support more than its minuscule population? The answer is yes, and no.
The issue of how many people the continent can sustain has preoccupied Australians since European settlement.
In the 19th century many imagined Australia becoming a second United States. Only slowly did it dawn on them that such a dream might be unrealistic.
Among the first to question it was Charles Darwin, who after a visit to Australia in 1836 wrote: 'I formerly imagined that Australia would rise to be as grand and powerful a country as North America, but now it appears to me that such future grandeur is rather problematical.'
The problem lies in geography. A harsh climate and poor soils mean that only about 10 per cent of the continent is suitable for intensive agriculture. The rest - the vast inland area that Australians know as the Outback - is made up of scrub, sand dunes, salt pans and scrappy woodland.
In a best-selling book The Future Eaters, anthropologist Tim Flannery wrote: 'Even with all the benefits of irrigation and technology, our agriculture is at the mercy of the cycle that drives Australia's strange climate, the El Nino southern oscillation, which brings cycles of drought, fire and flood.'
The past 12 months have provided ample reminder of the vagaries of the climate. Last Christmas bushfires raged along the east coast. Then came floods which turned parts of the country into vast inland lakes.
And now it is in the grip of the worst 'big dry' for years, with 80 per cent of New South Wales declared drought-stricken.
Despite such physical constraints, Australia's population has increased by 2.5 times since 1945. Japan's invasion of Southeast Asia and the Pacific during World War II terrified Australia's leaders. They were only too aware of the vulnerability of the country.
Under the catch-cry 'populate or perish', Australia encouraged a wave of post-war immigration, first from Britain and Ireland, and then southern and eastern Europe.
Now the debate is over whether Australia's population should continue to increase. Environmentalists argue that the country is already suffering from serious environmental degradation, from rising salinity to water shortages, and taking in more people could herald disaster.
Business leaders, on the other hand, point out that a healthy economy needs a constant influx of new workers. And politicians are mindful of falling fertility rates and an ageing population, and the burden that will put on a dwindling workforce.
Between them they argue that Australia should dramatically increase its population to as much as 50 million by 2050.
I tried to explain some of this to the taxi driver, but he was not convinced. For him the equation was simple. A big country requires a big population. Perhaps he envisaged a string of mini-Singapores dotted across the wide brown plains. At least the traffic jams would not be so bad.