Federal prisoners who identify as humanist can now celebrate Darwin Day and get accommodations typically afforded to those inmates who believe in a deity.

The federal Bureau of Prisons agreed in the settlement of a lawsuit to add a section on humanism to its manual on inmate beliefs and practices. Officials in the prison system will also consider requests from humanist inmates for access to study materials, observance of holy days, and time and space for religious activities.

Inmate Jason Michael Holden and the American Humanist Association filed the lawsuit last year, saying Holden and other humanist prisoners were prohibited from forming a study group at a federal prison in Sheridan, Oregon.

Humanism is similar to atheism. But rather than simply reject belief in a god, humanists advocate rational thinking.

"There's not much to talk about in respect to just atheism," Holden's attorney, Monica Miller, said by phone from Washington, D.C. "It's really about what you do believe, and what those worldviews are and what those philosophies are."

The settlement comes a little more than a year after the U.S. Army added humanist to its list of religious preferences.

It is unknown how many inmates identify as humanist. But giving them the ability to choose that preference, and to have it entered in the federal prison database, will allow the number to be calculated.

Holden has been imprisoned since an armed robbery in Washington state more than a decade ago. He explained in a May 2014 interview with Uptown Radio that not all atheists — such as those who are white supremacists — are humanists.

"As humanists, we believe in the ability of mankind to transcend their differences and find some common ground, you know, make the world a better place," he said.

Sheridan prison officials allowed Holden to form the study group after the lawsuit was filed. Under the settlement, Holden can maintain the group as long as there are at least two like-minded prisoners, and the option will be afforded to humanist prisoners elsewhere.

Darwin Day is celebrated Feb. 12, the birthdate of Charles Darwin. Those who observe the day use it to highlight science. Miller said the inmates could perhaps watch a video to mark the occasion and have some type of snack.