There’s almost nothing more important than fertility in determining a nation’s future viability.
Demographers suggest that a country needs a fertility rate of just over two children per woman to hit “replacement fertility” — the rate at which new births fill the space left behind by death.
But due to certain cultural and economic forces, only about half of the world’s 224 countries currently hit replacement fertility.
For them, encouraging people to have sex can involve strategies that range from the highly explicit to the downright bizarre.
Is that Boyz II Men I hear?
If you aren't going to have a kid for your own family, Danes are told, at least do it for Denmark.
No, literally, do it for Denmark.
The small Nordic country has such a low fertility rate -- around 1.73 children per woman -- that Spies Rejser, a Danish travel company, has come up with ingenious incentives to get people under the sheets.
First it was three years of baby supplies for couples who conceived on a vacation booked through the company.
Now it's a sexy campaign video entitled 'Do it for Mum,' which guilts couples into having kids if only to give their precious mothers a grandchild.
Vladimir Putin once brought Boyz II Men to Moscow to rile men up right before Valentine's Day.
Can anyone blame him? As Tech Insider recently reported, the country is experiencing a perfect demographic storm. Men are dying young. HIV/AIDS and alcoholism are crippling the country. And women aren't having babies.
The problem got so bad that in 2007 Russia declared September 12 the official Day of Conception.
On the Day of Conception, people have off from work so they can focus solely on having kids. Women who give birth exactly nine months later, on June 12, win a refrigerator.
Japan's fertility rate has been below replacement since 1975.
To offset that decades-long trend, in 2010 a group of students from the University of Tsukuba introduced Yotaro, a robot baby that gives couples a glimpse at parenthood.
If men and women begin seeing themselves as fathers and mothers, the students theorised, they will feel emotionally ready to take a stab at the real thing.
The 1960s in Romania were a perilous time for couples.
The idea was: If you weren't contributing to the Communist state with future labour, you had to contribute with your dollars.
The 80s weren't much better, however, as women faced forced gynecological exams performed by 'demographic command units' to ensure pregnancies went to term. When Romanian leadership changed in 1989 the brutal policy finally came crashing down, but at 1.31 children per woman, the fertility rate is still well below replacement.
Singapore has the lowest fertility rate of any country in the world, at just 0.81 children per woman.
Sensing trouble, on August 9, 2012, the Singaporean government held 'National Night,' an event sponsored by the breath mint company Mentos to encourage couples to 'let their patriotism explode.'
The country has also placed a limit on the number of small one-bedroom apartments available for rent to encourage people to live together and, presumably, procreate.
Each year the government spends roughly $US1.6 billion to get people to have more sex.
On the third Wednesday of every month, South Korean offices shut their lights off at 7pm. It's known as 'Family Day.'
In 2014, a dwindling number of people in India's Parsis community led to a series of provocative ads, such as the one that read 'Be responsible -- don't use a condom tonight.'
Another, geared toward men who still lived at home, asked, 'Isn't it time you broke up with your Mum?'
The Parsis community shrunk from roughly 114,000 people in 1941 to just 61,000 in 2001, according to the 2001 census.
However, the ads do seem to be working: By the latest measure, the population has inched back to 69,000.
NOW WATCH: Briefing videos
Business Insider Emails & Alerts
Site highlights each day to your inbox.