Happy Birthday to the seven-billionth young’un on the planet. But: D’oh! Who’s going to change my  Gen X diapers when I’m 80? Whose salaries are going to be taxed to hell and back to pay my Medicare?:

The precipitous drop in fertility in many nations caught demographers by surprise, said Linda Waite, director of the Center on Aging at the University of Chicago. No one realized until relatively recently that fertility rates would keep dropping even when women began having fewer than two children, she said.

“It’s sort of a head slap,” Waite said. “It wasn’t even talked about. It was more an unspoken assumption that fertility would fall to replacement and then stabilize.”

“There are many countries, more all the time, that are going to be looking at a population implosion, rather than a population explosion,” said Matthew Connelly, a Columbia University professor of history and the author of “Fatal Misconception: The Struggle to Control World Population.”

The aging of the world will change cultures in myriad ways. People may have to extend their working lives far beyond the traditional retirement age. Countries may start competing for immigrants. Across the planet, vast numbers of people already are migrating from high-fertility countries to those that need workers.

More:

The demographic transition is a significant factor in the financial crisis in Europe and the ongoing debt debate in the United States. In both places, the number of workers will steadily and dramatically decrease in relation to retirees. In the United States, the ratio of working-age people to retirement-age people will go from about 5-to-1 to 3-to-1 in the next two decades, according to the Census Bureau.

And America is a juvenile country compared with Japan, where, by mid-century, the 65-plus cohort will reach 40 percent of the population. If the trend holds, there will be just one working-age person per Japanese retiree.

“It’s a big, big social change. Lots of things are going to be disrupted,” said Ted C. Fishman, author of “Shock of Gray,” a 2010 book whose subtitle frames the issue comprehensively: “The Aging of the World’s Population and How It Pits Young Against Old, Child Against Parent, Worker Against Boss, Company Against Rival, and Nation Against Nation.”

Fishman points out that this isn’t all bad, although it is a challenge:

“Longer life is what human beings have wanted ever since we started talking to spirits and mixing herbs in bowls. And we worked at the top of our intelligence to get to this point of our life. It took almost the sum total of human history to get it. And now we have to work at the top of our intelligence to solve the social challenges that come with longer life and aging societies.”

Seriously, this is going to get scary if we’re not careful. Watch for a big push to normalize euthanasia.