"When Irish Eyes are Smiling" is an Irish tribute song written in the 1940s.  Its opening line goes, "There's a tear in your eye, and I'm wondering why, for it never should be there at all."  Are any tears being shed in Ireland these days?  If so, why?

Last week, Irish voters cast their ballots to repeal one of the most restrictive abortion laws in the world, passing their measure by a two-to-one margin.  This is perhaps not all that surprising, since in the past three years, Ireland installed a gay prime minister and voted to redefine marriage to include same-sex couples.

Progressive eyes are smiling in Ireland, grinning ear to ear, as they become San Francisco or Seattle.  The unborn, however, now face a suction tube or a curette.  Four-D ultrasound technology shows unborn babies smiling as early as 26 weeks, blissfully unaware of the perils now awaiting some of them in Ireland.

Irish citizens too might be blissfully unaware of the perils that await their country in the generations ahead, given the hard laws of demographics.

Demographics teaches that in order to sustain a population, the birth rate must exceed the death rate, leading to a net gain in population.  Since not all children reach adulthood and not all adults reproduce, a society or country needs each adult couple to produce slightly more than two children – two to replace the adults and a fraction to replace those who cannot or do not reproduce for whatever reason.

This replacement rate number is 2.1 – each couple needs to have, on average, 2.1 children to create a stable population.  A higher rate leads to a growing population, while a lower number indicates a shrinking population.  Many other countries are also in decline, with a fertility rate below the replacement rate – Italy, Germany, and Spain around 1.3.

Ireland's recent referendum works against the laws of demographics.  Same-sex couples cannot reproduce based on biology.  Sure, they can adopt or hire surrogates, but every same-sex couple takes two opposite-sex couples out of the pool for potential reproduction.  Similarly, abortion eliminates the product of reproduction at an early stage, killing babies who will never grow into adults, potentially having children of their own.

Ireland currently has a fertility, or replacement, rate of 1.9, less than the population-sustaining level, meaning a population in slow decline.  That's the native Irish population.  What about immigrants to Ireland?  Who, specifically?

In neighboring England, a chap named Tommy Robinson was arrested over his "anti-Muslim" activities, specifically for standing outside a court building filming and reporting on trials of radical Muslims involved in gang rape and grooming young girls for sexual assault.  It's his reporting on the latter trial that violated a previous probation order, landing him in a British jail.

This has nothing to do with the Irish ballot referendum, except to point out that much of Europe is experiencing a wave of immigration of people from religions and cultural backgrounds that differ from the native populations of the countries they are immigrating to.

According to the Pew Research Center, Ireland is 1.4 percent Muslim, a smaller percentage than the U.K. at 6.3 percent.  The Muslim fertility rate is 2.6, higher than Ireland and a full point higher than the E.U. average at 1.6.

In addition, Islamic law doesn't permit abortion or diverge from the longstanding definition of marriage.  Islamic abortion law is quite restrictive.  In cases of danger to the life of the mother, abortion is allowed, but only "[b]efore the time when the soul has been infused into the body."  The soul is believed to be in the body when "[t]he fetus starts to move inside the womb," called quickening, which can occur between 13 and 25 weeks into pregnancy.

While Ireland currently has a small Muslim population, conditions are ripe for this population to grow.  The native Irish population, already reproducing below the replacement rate, has legalized two activities that will further reduce population growth: abortion and the redefinition of marriage.

An immigrant population, already reproducing at a rate guaranteeing a rapidly growing population, has no such constraints, as its laws and culture forbid abortion and restrict marriage to its natural bounds.

Dublin mosque.

Islamic Cultural Centre of Ireland (Wikipedia).

Despite one's political view on social issues, demographics doesn't care about diversity, tolerance, or virtue-signaling – just as a wind turbine, producing green sustainable energy, cares not a whit about animal rights, PETA, and the birds it chops up with its spinning propeller.

The trend is apparent in other neighboring countries – Belgium, for example.  While Belgium's Muslim population is just over 6 percent, it is a breeding ground for jihad.

Liberal ideas seem full of virtue and compassion, and in the short term, they sound noble.  Long-term, however, they lead to despair and destruction.  Whether raising the minimum wage or providing "free" health care, such programs always end up damaging those they are designed to help – just as the wind farms destroy an important component of the same ecosystem they are trying to protect.

Ireland may be the next country on the list to face a demographic reckoning of its own creation, and one its people won't like.  Then Irish eyes won't be smiling.

Brian C Joondeph, M.D., MPS is a Denver-based physician and writer.  Follow him on Facebook, LinkedIn, and Twitter.