Eventually, the calling he felt from God became too powerful to ignore. The promising neuroscientist left the Ivy League research laboratory — and entered seminary at Catholic University of America in Northeast D.C. to become a priest.

“This constant intuition — I almost want to say nagging — that maybe I was called to serve in a different way… it was always frequent,” he said. “At different times the question would come back: If I see myself 90 years old, close to death, would I say to myself, ‘I should have entered seminary’?”

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He entered. And now, within the church, he hopes to help Catholics understand scientists, and scientists understand Catholics.

Scientists are a secular lot, on the whole. While 95 percent of Americans say they believe in God or some other higher power, just 51 percent of scientists do, according to a 2009 Pew study. But many of them quietly believe. And a small but significant number are turning from research to the priesthood, bringing a science-based perspective to the Catholic church that many church leaders say is greatly needed.

When Maldonado-Aviles arrived at Theological College, the Catholic University seminary, many of his classmates were young men just out of college. But he also found among his peers a seminarian with a PhD in chemistry, another who studied nanoscience, another who first went to medical school.

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The number of seminarians in Washington who studied the sciences, at least as undergraduates, is high enough that Cardinal Donald Wuerl, the head of the archdiocese, has noticed it. “Here they are, saying, ‘There’s more,'” he said about those seminarians who seek God after finding science first.

Ken Watts works as a recruiter for Pope St. John XXIII Seminary, a unique school in Massachusetts open specifically to men over 30 — sometimes many decades over 30 — who decide they want to become priests. By far the most common first career for these men is education, he said, followed by healthcare, military service, social work and other religious work — all fields that logically might lead to the priesthood. But he’s guided scientists to seminary quite a few times.

“They seem to fit in pretty well, is all I can say. There doesn’t seem to be a terrible struggle for them to bring their scientific backgrounds through the front door here. Nobody asks them to abandon it,” Watts said. “When the moral issues are those that revolve around medical, scientific areas, it’s certainly helpful to have people who really understand that world to help refine and clarify the church’s thinking on this.”

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Suzanne Tanzi, a spokeswoman for Theological College who noted the several scientists who have enrolled there, said scientist-priests are particularly helpful given one of the primary focuses of the current pope, who in fact was once a chemist himself: the environment. Francis’s first major writing as pope was a highly technical treatise on the environment, and the church has been an increasingly vocal advocate worldwide for policies to reduce climate change.

As Watts put it: “They’re very, very valuable.”

Maldonado-Aviles’s thoughts about the priesthood started early, as a youth growing up in Puerto Rico. He participated in mission trips as a high schooler, and started wondering what it would be like to grow up to be a missionary.

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Instead, he studied biology at the University of Puerto Rico, where he earned a fellowship for honors students through the National Institutes of Health. After he earned his doctorate at the University of Pittsburgh, he went into a post-graduate program at Yale, where he spent six years. He became particularly interested in researching the molecular basis of eating disorders.

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Almost three years ago, he got a job offer that seemed perfect: a tenure-track position doing research at the pharmacy school at the University of Puerto Rico. The job would bring him home to be closer to his family, which he had been wanting. It would mean longterm stability, a good salary and the chance to do interesting, meaningful research.

And after much debate, Maldonado-Aviles turned down the offer.

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“I have to seriously explore these questions,” he decided. And his process of priestly formation began.

That requires two years of philosophy, which some candidates complete while they are undergraduates, followed by four years of theology. For Maldonado-Aviles, who never studied either subject, that means six years of schooling. Now, at age 37, he’s in his third year.

If he continues on pace, he’ll be over 40 when he becomes a priest. That makes him older than more than 80 percent of newly-ordained priests in recent years, according to statistics from the U.S. Conference of Catholic Bishops, but far from the oldest. So-called “second vocation” priests have always been a presence in seminaries. American seminaries in 2016 ordained six men in their 50s and three in their 60s.

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Moving back into a dorm, Maldonado-Aviles has given up some things: He doesn’t earn a salary, instead living with his fellow seminarians where the church takes care of his needs. He can’t visit his family in Puerto Rico as often.

And he used to date, and assumed he would someday marry. Now, he anticipates a life of celibacy if he becomes a priest.

“I wouldn’t say that I’m making more sacrifices” than someone in a marriage, which requires sacrifices of its own, he said. “If I believe God is calling me to be a priest, I also believe he will give me charisms — gifts — that will help me.”

Maldonado-Aviles is careful to say that he does not know yet that he will certainly become a priest. The time he spends in seminary is all part of his process of discernment: Reading the clues that God has left for him that point to the path he’s meant to take. He saw some of those signs long before he entered seminary — times he heard a particular Biblical passage in Mass and felt it was calling personally to him to radically devote his life to Jesus, for instance.

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He seeks these clues with a diligence and precision that hearkens back to his first career.

He said he used to feel like the only one in the lab who believed in God — until he started seeing Yale professors filling the same pews he sat in at Mass. His work studying neurons led him to marvel all the more at God’s handiwork: “The complexity and yet the order in which things work in our body and in our brain, it makes you think there’s more than just randomness.”

But reconciling his faith and his work wasn’t always so easy. He remembers going to a talk about the development of the human neocortex, and realizing that the research being presented had been conducted on aborted human embryos in Europe.

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He was shaken to think that his scientific career might bring him in contact with abortion, which the church teaches is a grave sin. “What is it that I’m doing? Would I ever compromise my faith based on the pressure for success?” he wondered.

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Now, he says he has a deep interest in bioethics. Inspired by a handful of priest-scientists around him at Catholic University and some of the greats of Catholic history — priest Georges Lemaitre who first came up with the Big Bang theory, monk Gregor Mendel who originated the study of genetics — he envisions a potential future bridging the two realms. He wants to advise scientists on the ethics of their work.

“Theology has to learn from the scientific advice. We are informed as to how life works. But science also has to learn from theology,” said Maldonado-Aviles as he headed into the imposing stone seminary where he lives and prays — a student, and someday a teacher, of both.