That decision changed the course of their lives. The same could probably be said for many of the Peace Corps' more than 200,000 volunteers, many of whom will descend on Washington, D.C., this weekend for the Peace Corps 50th anniversary celebration, Sept. 24.
Shirley, now 63, developed an affinity for Africa when he represented Tanzania in the Model U.N. in high school. That interest grew at the California Institute of Technology, and though he applied to graduate schools as well, his first choice came through when he was accepted into the Peace Corps.
Within a few weeks of graduating from college in 1969, he arrived in Sierra Leone.
Shirley taught high school math in the town of Bonthe for two years and ended up staying for a third year to help institute a curriculum change that was sweeping across West Africa.
Though he never intended to be a math teacher — let alone a teacher of math teachers — Shirley briefly came back to America before returning to Africa, this time to train math teachers at Ahmadu Bello University in Nigeria
"I went to Nigeria only intending to stay for three years, and I ended up staying for 15," he said. "Partially because I liked the job, but also because life caught up with me."
Life, as it turned out, became a Ghanaian woman named Alberta Ohenewah, whom he married and had two children with.
They lived in Nigeria until 1988, when he decided to move his family back to America. He had finished his doctorate and believed American high school would be better for his children should they wish to go to college here.
More importantly, after nearly two decades as a math teacher in West Africa, Shirley felt his work there was finished.
"When I first went to Nigeria, the university was staffed by ex-patriots," Shirley said. "But Nigeria was growing and producing its own staff. Most of the teaching staff was Nigerian. There weren't many Americans or Europeans left. (Leaving) seemed like the right thing to do."
The trans-Atlantic interview process proved difficult, but Shirley swung a one-year teaching gig at Northern Illinois University, and from there, landed at Towson University, where he began as a math professor and has ascended to acting dean of graduate studies.
"Many times people say how the Peace Corps changed their lives," Shirley said. "In my case, it's more than most. I wasn't really planning a career in math education, and it's been my career ever since."
Cook's decision to join the Peace Corps was a bit more spontaneous. After graduating from the University of Richmond in May 1965, she intended to go to a seminary for her master's degree in church music and become a church choir director.
Instead, she married Richard Cook on Aug. 14, 1965. The newlyweds reported to Peace Corps training 23 days later.
"I would have never done that alone," said Cook, now 67. "But that's what he was going to do, so if I wanted to marry him, I had to join the Peace Corps."
Six married couples began training at Camp David, a jungle camp in Puerto Rico that provided intensive language training and cultural lessons. Just one other couple — another pair of newlyweds — made it through the three-month training session.
From there, the couple reported to an urban slum in Panama. Richard Cook helped build concrete paths and steps in the hillside village, allowing residents to retrieve water without slipping down the muddy slopes.
Barbara Cook taught music and introduced the village women to family planning. She planned to teach sewing, only to learn the women knew much more about it than she.
"The whole issue of our going down there and thinking we have something to teach people is paternalistic, and it's natural for one to think that, but these ladies are just so much more talented than one gives credit for," she said.
Like many Peace Corp volunteers, Cook was touched by what she saw.
"Watching people love life and have fun on nothing was a wonderful lesson for life, and I never forgot that," she said. "I learned not to whine. All I have to do is remember the lady next door who was trying to raise four kids with a dirt floor and a little fire. I'll never forget."
The couple's spontaneity didn't cease after the Peace Corps. After living in New York for a short time, Richard Cook decided to move across the country to organize grape and lettuce boycotts with Cesar Chavez and the United Farm Workers Union.
"Again, I went along for the ride," Barbara Cook said. "Off to California with two babies."
The couple's third child was born while they were working with the UFW in St. Louis, and Barbara Cook began to think of a more permanent future. She applied to medical school.
"Everybody laughed at me," she said. "I was 32, I had three kids — nobody was accepting women like that."
But she was successful — thanks to her time in the Peace Corps.
The dean of students that interviewed her at St. Louis University was from Puerto Rico. Sensing an opportunity, she spoke to him and interviewed in Spanish.
"He thought I had spunk and put my name forward to the committee," she said. "They never accepted a woman over 30. They never accepted a woman with three kids, so I had a job to do. I needed to make it, and I needed to be successful to pave the way for other women who have that same goal."
She did just that. From beginnings with the Public Health Service at a miners' hospital in West Virginia to her becoming president of the Johns Hopkins Community Physicians, Cook has excelled wherever she's found herself.
She was the first woman elected to the Board of Governors at the Ochsner Clinic, in New Orleans, and, in 2010, was named the Dr. Sebastian Russo Award Memorial Winner, given by the Baltimore City Health Department to a doctor who provides low-income individuals and families with health care.
Without her decision to join the Peace Corps, none of it might have happened.
"Growing up in the South, I was supposed to get married, have babies and be a housewife," she said. "That was the path I thought I was heading down, but I've had a spectacular career that I never dreamed I would ever have."
World of difference
Though their lives now play out largely within the United States, both Shirley's and Cook's families have a worldly flavor. Of her three children, only Cook's son Ben lives in America. Her son Matt lives in Costa Rica and her daughter, Sarah, lives in Mexico City. Cook had planned on attending this weekend's celebration in Washington, but instead will be visiting her daughter.
Likewise, Shirley's family has grown into a worldly one. His half-daughter, Takyiwah, still lives in Ghana, and his son, Jefferson, lives with his wife in Scotland. His daughter, Emily, still lives in the area.
While they lead separate lives on separate continents, the Shirley family returned to Ghana under the saddest of circumstances last summer. After 36 years of marriage, Shirley's wife died and the family went back to her homeland so she could have Ghanaian funeral rites.
Going forward, he hopes to get back under better circumstances.
"I very well may be doing more work in West Africa when I retire," he said. "There's a couple of opportunities that have come up. I don't know for sure what I might do, but there's that possibility that I could go back.
"Who knows? I could even become a [Peace Corps] volunteer again."