This goes for individuals as well as societies.
- Some people go vegan quickly (a few) others do it slowly (the majority).
- Social trends regarding animals tend to change slowly, then there's a tipping point (critical mass) where it changes quickly.
Gradual social change regarding animal testing:
Gradual social change regarding fur:
These images are from Gallup polls.
Here is the link: http://www.gallup.com/poll/1681/Moral-Issues.aspx