Scientists, teachers, students — even preschool kids — are joining in on the March for Science in San Francisco and across the nation Saturday.

More than 1,000 people have gathered at Justin Herman Plaza across from the Ferry Building, where several speakers are scheduled to talk before the march moves up Market Street and ends at Civic Center. At one point, the crowd could be heard yelling, "Science not silence!"

Organizers say the purpose of the march is to celebrate and stand up for scientific research and promote the use of evidence-based science in public policy.