They have been spurred in part by DNA evidence made available in 1998, which almost certainly proved Thomas Jefferson had fathered at least one child with his slave Sally Hemings.
The cumulative effect was a fundamental change in how millions of people approached life itself, a reversal of attitude that must rank as one of the largest in human history.
One thing is for sure, if or when the U.K. leaves the EU, it will erect new logistical and economic barriers, and no one knows how divisive they will be.