Blogger JayMan (a member of the HBD 23) has an interesting post up about the rise of universalism (i.e. tolerance, social liberalism) over the last century or so.  There have been several theories proposed to explain this:

1) Pumpkin Person’s Theory:  The Flynn effect.  I’m probably not the first person to think of this, but it seems to me that as 20th century nutrition increased brain size, neurological development, and thus IQ over the last several generations, people became more moral, open minded, and inclusive, because social liberalism is positively correlated with IQ for reasons I’ve explained here.  Add to that the rise of education and people would have become especially enlitended.

2) HBD Chick’s theory:  Outbreeding in Northwestern Europe caused a rise in universalism and related values.  HBD Chick (a member of the HBD 23) writes:

the individualistic guilt-culture of northwest (“core”) europeans today came into existence thanks to their extensive outbreeding during the medieval period (…and the manorialism). the outbreeding started in earnest in the 800s (at least in northern france) and, as we saw above, by 1050-1100 thoughts on individualis began to stir. around the same time, communes appeared in northern italy and parts of france — civic societies. violence rates begin to fall in the 1200s, especially in more outbred populations, i would argue (guess!) because the impulsive violence related to clan feuding was no longer being selected for.

by the 1300-1400s, after an additional couple hundred years of outbreeding, the renaissance was in full swing due to the “wikification” of northern european society — i.e. that nw europeans now possessed a set of behavioral traits that drove them to work cooperatively with non-relatives — to share openly knowledge and ideas and labor in reciprocally altruistic ways. the enlightenment? well, that was just the full flowering of The Outbreeding Project — an explosion of these not-so-nepotistic behavioral traits that had been selected for over the preceding 800 to 900 years. individualism? universalism? liberal democracy? tolerance? reason? skepticism? coffeehouses? the age of enlightenment IS what core europeans are all about! hurray! (^_^) the Project and its effects are ongoing today.

3) Bruce Charlton’s theory:  Dysgenics.  Professor Charlton argues that an accumulation of recent mutations over the 20th century has caused genetic fitness reducing social attitudes.  He writes:

It is possible, perhaps even plausible, that the usual type of explanation for the self-hating, self-destructive insanities of New Left Political Correctness may be insufficient – and that in reality the core, permissive, necessary factor has not been socio-political but instead biological.

4) Joshua Gamson’s theory: According to Yale sociologist Joshua Gamson (author of the book Freaks Talk Back), the prevocative 20th century daytime talk shows, pioneered by Phil Donahue, but popularized and reinvented by big brained Oprah in 1986, and taken to extremes by Ricki Lake and Jerry Springer, created a kind of confession culture that gave gays and other marginalized groups a valued cultural space.  Although this genre was often dismissed as freak shows and trash TV, they would eventually be recognized as a major counter culture movement, causing Time magazine to rank Oprah as the most influential woman on the planet.

Several hosts from the glory days of day time talk shows source:

5) J.P. Rushton’s theory:  Professor Rushton mentioned that following World War II, there was such a strong backlash against Nazi Germany that the pendelum has swung to the opposite extreme: Political correctness and hostile opposition to anything even resembling racism.

6) Kevin MacDonald’s theories:  Professor MacDonald ( a member of the HBD 23) argues that  Northwest Europeans evolved a kind of pathological altruism because as hunter/gatherers during the ice age, they didn’t have the luxury of nepotism or ethnocentricism.  The ice age was so tough to survive that tribes had to embrace the smartest, most moral people, whatever their genetic background.  MacDonald argues that this natural uinversalism of Northwest Europeans has been amplified by Ashkenazi Jews who promote liberalism as part of a group evolutionary strategy to thrive in Western Cultures.

However in his post this weekend, blogger JayMan seems to reject such ideas, writing:

Many commenters on this matter like to blame Jewish influence for these shifts in social attitudes, and it is true that Ashkenazi Jews commonly hold and have promoted progressive agendas. But what these commenters ignore is this: why do people listen? Or more the point, why have some people (and peoples) embraced these views and not others? A promoted agenda is only as good as the traction it gains. Clearly, the trend towards universalism has been the purview of Northwestern European societies almost exclusively. If Jewish influence has had any role, it is only in the form of a rush in a much larger prevailing current.

Indeed, Jews are a vanishingly small portion of the population in many of the most progressive countries, such as the Scandinavian ones. Sweden for example is known for being a foremost champion of progressive causes.