My mom celebrated a birthday yesterday. I hope she won't mind my telling you all that it was number 71. Earlier this week, she was in Atlanta meeting with potential clients and discussing healthcare informatics technology with people from the CDC. Though she "retired" from a 30-plus year career with the City of Philadelphia in the early 1990s, she has remained extremely busy and is, in many ways, at the top of her game as an accomplished professional in the field of public health.

She is also very much the exception among members of her generation. The pre-Baby Boom cohort (b. 1925-1945, sometimes labeled "The Silent Generation"), was considerably smaller than the Veteran Generation (b. 1905-1925) that came before it and the Baby Boom (b. 1946-1962) that followed. Their moment as cultural movers and shakers came early, as the first flush of the counterculture in the 1950s and early 60s, and later as leaders of the Civil Rights and Women's movements. They were never numerous enough to dominate American society or the workforce, and their generational personality as negotiators, conciliators, and advocates for fair play ran hard against the secular, status-quo arrogance of the Veterans and the ideological stridency of the Boomers.

One thing that was in their favor was economics. Although they were born into the Depression and World War II, they grew up in the booming postwar economy where America dominated world trade and manufacturing. Jobs were plentiful, benefits negotiated to keep the labor peace during the war years were institutionalized to provide stability and dignity for workers up and down the occupational ladder, and the government invested lavishly in infrastructure, education, research, and culture as the US rose to superpower status. When they were buying homes in the 1960s and 70s, real estate was cheap and interest rates were low. As they entered their prime earning years in the 1980s, the economy and the stock market boomed, lifting salaries and investment yields for those already well-established in the middle class. When it was time to retire, many could rely on fixed-benefit pension plans, fully-funded Social Security and Medicare benefits, massive appreciation of their investments and real estate assets, and the proceeds of a lifetime of savings instilled by the thrifty habits acquired in their Depression-era youth. In the last few years, the wealthiest Silents also got the benefits of the Bush tax cuts in 2001 and 2003, further augmenting their relative position in the economy.

Consequently, the pre-Baby Boom generation has had little incentive to stick around in the workforce. As of 2005, Silents comprised only 8 percent of the US working population. Over 95 percent had formally retired to collect benefits by 2007, and those still working mostly did so as part-timers and volunteers. Don't tell that to my mom, of course, or to Warren Buffett, John McCain, Hugh Hefner, or any of the other prominent septegenarians still making their influence felt in the executive corridor.

But the bottom line is that the influence of this fourth generation in the workplace - which was never fully-felt because of its small numbers - is receeding precipitously. As more and more Boomers pass the six decade mark, it is their outlook and their values which will define older adulthood. We are seeing this already with the flood of retirement investment ads featuring music and personalities associated with the 1960s, and copy aimed at appealing to Boomer idealism rather than Silent prudence.

Since my work is mostly future-oriented, I prefer to talk about three rather than four generations in the US workforce. This isn't meant as a slight to the Silents, whose contributions and fair-minded workstyle will be greatly missed, but it does reflect the statistical realities. The leading edge of the Millennial generation (b. 1981-2000) already outnumbers the remaining Silents in paid, full-time positions. As we move into the 2010s, it is they, the Boomers, and GenX who will define the generational blend at work. We won't see a fourth generation in the workforce again until the 2020s, when the first batch of post-Millennials will start appearing - doubtless to a chorus of concern and a flurry of new adaptation.