Steve Sailer asks: "Is there anyway to look at cohorts over time to see if ethnocentrism increases with age? I suspect ethnocentrism sets in more when you start thinking about grandchildren, but that's just a guess."
The GSS question on one's closeness to his ethnic group (ETHCLOSE) was asked in 1996 and 2004. I calculated the mean score for all whites in their 50s in 1996 and got 2.84. Next, I computed the mean for people ages 58-67 in 2004 (since the earlier group had aged 8 years). Their mean is 3.12, almost one-third of a standard deviation higher. The difference is not quite significant at the two-tailed 95% confidence level, but the small samples (143 and 137) do not help.
I take this as evidence that Steve is right: tribalism rises as you reach the age when grandchildren are in your thoughts.