For starters, consider the timing. It's true that inflation-adjusted male earnings were lower in 2008 than they had been 25 years earlier in 1973. But at the same time, inflation-adjusted male earnings were much lower in 1948 than they were either 25 or 50 years later. So by this theory we would have expected very low marriage rates in the poor late-1940s—even lower than we see today—which of course isn't the observed pattern. What's more, male earnings experienced a substantial local increase over the course of the 1990s that wasn't matched by any localized turnaround in the marriage trends.
Sure, and male wages were even lower in 1648. But wages that are stable or rising wouldn't be expected to have a negative impact on marriage rates. Steeply dropping wages, however, might, as young men increasingly lose their sense of self-worth, become less attached to the workforce and less attached to traditional bourgeois values, and become less attractive mates to young women. And since this is a four-decade trend, there's no reason to think that a brief upward blip in the 90s would have much effect.
Matt prefers a different explanation:
I continue to think the common sense explanation here is that we're witnessing the consequences of increased labor market opportunities for working class women, rather than diminished labor market opportunities for working class men....As women's labor market opportunities have increased, they've got choosier about entering into marriage. It's true that in pure economic terms even a low-quality husband is a net benefit to the household, but there's more to life than pure economic terms.
Sure, I agree. That's the flip side of declining male earnings, and it's almost certainly part of the picture. But keep something in mind: poor and working class women have always worked outside the home in significant numbers. It's middle-class and upper middle-class women who have been the biggest beneficiaries of increased labor market opportunities, and yet that's precisely the class that's seen the least change in marriage habits. What's more, this increase in labor market opportunties has been true throughout the Western world, but marriage trends nonetheless vary pretty widely among developed countries. So the data here isn't all that clean after all.
Again: this is almost certainly a complicated issue with multiple causes. Lower male earnings and higher female earnings are probably both part of the picture. Changing social mores are probably part of the picture. Increased welfare payments to families with children are probably part of the picture. Overall economic growth is probably part of the picture. I'd be very hesitant to embrace any monocausal explanation — not Charles Murray's and not mine. It's complicated.