The bigger your family, the more liberal it probably is.
I’ve now used evolutionary psychology theory to help explain why populations with high proportions of immigrants (Part 1 of 3) and young people (Part 2 of 3) would be more liberal. Those conditions are more strongly associated with the Openness psychological trait, and that trait correlates strongly with liberalness.
But the other important implication of a low average age is bigger average family sizes. Bigger families mean more children, including a greater proportion of the population born second or later — and it turns out that first-born children are more likely to score highly on Conscientiousness (and therefore hold conservative beliefs), while younger children are more likely to score highly on Openness (and therefore hold liberal beliefs).
For example, one study of Japanese-Americans (PDF) “found that first-borns were 1.4 times more likely to vote for conservative political candidates than their younger siblings.” The authors of another study (PDF) “estimated that later-borns are between 20 and 43 percent more likely than first-borns to support a liberal political position, to back a liberal candidate, or to campaign for a liberal social cause.”
If you game it out, it makes sense. First-born children are more likely to have to take care of younger siblings and are likely to get the most favorable attention from their parents. Those two factors would both give first born children a greater interest in being conscientious of authority and established hierarchies.
Meanwhile, younger children in a family are less likely to have to take care of fellow siblings. And historically at least (going back millennia), they were less likely to receive an inheritance from their parents. This would give them less of an interest respecting hierarchies that disadvantage them and more of an interest in being open to new and unfamiliar experiences that might bring them more resources.
And when you look at fertility rates in the U.S., guess what: comparatively liberal populations like African-Americans, Asian-Americans, and Latinos tend to have higher fertility rates — and thus a higher proportion of their population is made up of younger-born people. With more non-first borns in a population, we should expect the population to be more liberal.
As the first-born Simpson child, Bart may be evolutionarily predisposed to
a conscientious personality.
So Does This Break the Stalemate?
At the end of Part 2, I asked:
Immigration status and average age are two pretty good reasons why Hispanics overall might be more inclined to Openness, but it doesn’t seem to be showing up in these data. Hmm. Something’s gotta give. Maybe looking at family size and birth order will help break the stalemate?
Well, family size and birth order do give us another good reason to think Hispanics overall should be inclined to Openness, since Hispanics have a relatively high group-wide fertility rate and thus a lower percentage of Hispanics are first born in their families.
That is compelling, but I wouldn’t say it breaks the stalemate. At the end of Part 1, I noted:
A number of other factors, like income, education level, or gender, could be skewing these results. But to control for them and isolate race as a predictive factor in people’s personality traits…I’d have to do some serious regression analysis. Nuts to that.
And there are many other potential confounding factors. For example, an entire lifetime of partisanship has been shown to depend strongly on whatever the prevailing political mood was when someone turned 18:
So, ultimately, I conclude that factors such as recent immigration history, average age, and family size/birth order probably do have some impact on making white people more conservative and groups like Hispanics and Asian-Americans more liberal. But there are, to say the least, a richly woven tapestry of factors that is very difficult to unravel. As political scientists keep plugging away at these problems, hopefully a clearer picture will emerge.