Though not everyone sees an ancestral resemblance to Curious George when they look in the mirror, people worldwide will be able to celebrate both the 199th birthday of evolution theorist Charles Darwin and the annual Darwin Day today.

Even though Institute for Humanist Studies spokesman Duncan Crary said an estimated 43 percent of Americans deny the theory of evolution because of religious beliefs, U.S. residents still debate Darwin’s ideas on the theorist’s birthday.

“We take medicine when we’re sick, we have airbags in our cars to prevent us from getting injured,” Crary said. “There is an unending amount of benefits to our lives that are direct results of science, but we don’t often take the time to think about the science itself.”

He said more than 800 church congregations nationwide celebrated “evolution weekend” a few days ago. “It’s a chance for religious organizations to discuss the compatibility of science and religion,” Crary said.

Though the idea behind Darwin Day is enlightenment and learning, the holiday is meant to be fun, Crary said.

“When you think of science, you don’t often think of a party or a celebration,” he said. “It’s a chance to have a little bit of fun with science and to eat birthday cake, of course.”

Secular Student Alliance Executive Director August Brunsman said college students are the most active participants in Darwin Day celebrations. Brandeis University, Harvard University, Tufts University and Bentley College have secular or humanist student groups. She said there are more than 100 affiliate groups on campuses across the country.

“One of the most popular ways to celebrate Darwin Day is to get a table in the student union with birthday cake and literature about evolution and Darwin’s life in general,” she said.

People with non-theistic religious beliefs have said they enjoy Darwin Day because it gives them a chance to have a religious tradition of their own.

Ethical Society Without Walls ethical culture leader Susan Rose said because her religion is ethical culture and does not have the same traditional qualities of other religions, she appreciates a day to celebrate beliefs that match up with her own.

“I like to be able to share with other people the importance of science and reason,” she said.

Local Darwin Day events include the second annual Toast to Darwin at Redline in Cambridge and a screening of “Inherit the Wind” with discussion afterward at Revolution Books in Cambridge.