Final answer:
European parties on the political left tend to appeal mainly to urban professionals, representing a shift from previous trends where lower-income and less educated individuals were their main supporters.
Step-by-step explanation:
The question asks which group European parties on the political left tend to appeal mainly to. Historically, left-of-center parties in Europe garnered support from voters with low incomes and lower levels of education; however, Professor Thomas Piketty points out a shift in this dynamic. According to Piketty's analysis, urban professionals with higher education and income levels are now more likely to support liberal and leftist candidates, opposing earlier patterns where they might have aligned with right-wing parties. Meanwhile, working-class and less educated voters are found to trend towards conservative policies in recent years. This emerging trend has been an outgrowth of various factors, including changing class identities in politics, economic transformations, and the rise of communications technology.