Globally, the Parsi community is shrinking so fast from an ever- declining birth rate that India is now campaigning for Parsis to make childbearing a duty.
One such campaign advertisement earlier this year went: "Be responsible. Don't wear a condom tonight. Our numbers dwindle... Which is why, if you're married, maybe you should think about playing your part very seriously."
Very seriously indeed, so much so that the Indian government has set aside 100 million rupees (S$2.1 million) for a scheme to encourage Parsi couples to have more children.
The Parsis are people of the fire-worshipping faith known as Zoroastrianism, and had migrated from Persia to India in the seventh century to avoid persecution.
In India, where most of today's Parsis are, it is estimated that there are 60,000 of them, half as many as there were in the 1940s, the BBC reported in July.
The paternal lineage concept means I can marry outside, but my sister can't. Where (in the holy book) does it say so? Isn't it unfair? All these rules have to change. It won't affect the religion; in fact, it might help us to grow.
MR RUSTOM GHADIALI, president of the Parsi Zoroastrian Association of Singapore, on the practice of not counting children of Parsi women who have married non-Parsis as part of the community
Two key reasons for the decline in numbers: many in the community are not marrying - 30 per cent of Parsis never marry, and, if they do marry, they do so later in life, thus decreasing their chances of having children as a woman's fertility in general declines with age.
The Parsi community is more Westernised, with some delaying marriage till they are financially more stable, and Parsi women preferring to focus on their careers first and starting a family later.
But in Singapore, it seems that the Parsi community has bucked the trend, doubling to about 300 Parsis from 15 years ago.
More Parsi people have been coming from India and other countries to Singapore, mainly due to the job opportunities available here, says Mr Rustom Ghadiali, president of the Parsi Zoroastrian Association of Singapore (PZA). Most of them have become permanent residents. About a fifth of the 300-strong community today were born here.
Another reason for the different trends here and in India is the issue of who is, and is not, considered a Parsi.
The Singapore figures by PZA include non-Parsi spouses, who make up about 15 per cent of them. They also include about 50 Parsi children, including those of non-Parsi fathers.
But in India, if a Parsi woman marries out, her children are not deemed to be Parsi. More than a third of Parsis there marry non-Parsis. There are many more non-Parsis around - the Parsis have never accounted for more than half a per cent of India's population.
Even in the country's Jiyo Parsi campaign, which encourages the Parsis to procreate, only couples where the husband is a Parsi can get subsidies for fertility treatment.
As Zoroastrian scholar Khojeste Mistry told the BBC: "If (the women have) chosen to marry out, they've broken the rules of the religious customs and practices."
But Mr Ghadiali - who has been PZA's president for more than 20 years and is one of five Zoroastrian priests here - tells The Straits Times that this marriage condition is a man-made law and not in the Zoroastrian holy book.
"The paternal lineage concept means I can marry outside, but my sister can't. Where (in the holy book) does it say so? Isn't it unfair? All these rules have to change. It won't affect the religion; in fact, it might help us to grow."
He adds: "We only had knowledge of what happened in India... There was no condition about marriages when we were in Persia."
While some Parsi Zoroastrians like Mr Mistry say that people who marry out are "destroying the fabric of community existence" and not helping to preserve the Parsi ethnic identity, others like Mr Ghadiali say that holding such a strict view further "splits the community".
In India, some children were excluded from the community when they went against their parents' wishes and married non-Parsis.
There have also been cases in which Parsi women who married non-Parsis could not attend the funeral rites of their elderly parents.
Here in Singapore, the PZA was also divided for about 15 years, from the mid-1970s. Orthodox Parsis did not allow non-Parsis to attend PZA events, Mr Ghadiali says.
"Some family members can come, but some cannot come. Then what's the point of having an event?"
Then around 1985, the PZA committee amended its Constitution such that non-Parsi spouses can be members of the association, though they do not have voting rights.
"Today, we are one community. Whether you marry outside or not, your conscience has to be able to accept it," he says.
However, he reminds young people - including his two daughters who married non-Parsis - to be aware of the issues that come with marrying someone of another faith, such as having to follow different religious customs.
"We need to keep our minds open, and let the religion flourish," he says, noting that some children from mixed marriages decided to become Zoroastrians.
But what about the preservation of the ethnic identity of Parsis?
He says he does encourage people to marry and have children, but prefers not to force this upon people.
"Let us see what happens. Keeping people out is not going to help. Let's take people in," he says.