Many likely 2016 Republican presidential candidates have expressed opinions about mandatory vaccination this week amid a measles outbreak in the United States.

New Jersey Gov. Chris Christie kicked things off on Monday when he said parents should have “some measure of choice” to decide whether to vaccinate their kids.

But the vaccine question isn’t the first time potential GOP candidates have taken on questions of science.

Below are quotes from the possible candidates, suggesting where they stand on vaccines, climate change and evolution.