Even so, the marches were effectively protests against steep cuts that US President Donald Trump has proposed for federal science and research budgets and his administration's scepticism about climate change and the need to slow global warming.
"It's important to show this administration that we care about facts," said Chris Taylor, 24, who was part of an early crowd of about 2,000 who gathered on the Mall for teach-ins on topics like climate change, water quality and sustainable food.
"It just seems like they're not really concerned about economic growth or creating new technologies, just catering to massive corporations," said Taylor, who is earning a PhD in robotics at George Mason University in Virginia.
March for Science is the latest in a series of national demonstrations that have been staged since Trump's inauguration nearly 100 days ago. Previous marches and protests have focused on a range of partisan issues, from abortion rights to immigration policy.
The White House did not respond to a request for comment on Saturday's marches. However, in the past, Trump has said climate change was a hoax that was stifling policies to foster economic growth.
Trump's proposed 2018 budget calls for deep spending cuts by government science agencies, including a 31 per cent reduction for the Environmental Protection Agency.
The direct involvement by the scientific community in a national policy debate has stirred some criticism about whether scientists should get involved in politics. But organizers have defended the march as crucial because of the threat posed by discrediting scientific consensus and restricting research.
"As scientists, as human beings, our mandate is clear - it's to stand up for what we know to be true," said Kellan Baker, a senior fellow at Johns Hopkins School of Public Health and one of the speakers on the National Mall.
That theme was echoed by many of those who showed up in Washington for teach-ins, which organizers said were a centerpiece of the initial Earth Day held in 1970 to call attention to the environment.
"Science isn't respected and it needs to be," said Sarah Binkow, 22, a civil engineer who traveled from Pontiac, Michigan, to attend the Washington rally.
"Being here definitely gives me hope that there's this overwhelming population that supports science and supports scientific theory," she said.