Frank Alexander Welsh III, 77, a passionate lover of nature and professor emeritus of biochemistry, died Friday, April 2, at his Bryn Mawr home of leukemia.

Known as Dusty to his friends, Mr. Welsh enjoyed a distinguished 40-year academic career at the University of Pennsylvania School of Medicine. A member of the neurosurgery faculty, he loved teaching and mentored many young scientists until his retirement 10 years ago.

Mr. Welsh was also a respected scientific researcher, focusing on the area of stroke and cerebral blood flow, and he wrote more than 80 published peer-reviewed research articles.

Penn neurosurgeon and colleague M. Sean Grady said Mr. Welsh’s published research includes his collaboration with fellow scientist Katalin Kariko and her now-famous studies of messenger RNA. That, Dr. Grady said, is recognized as a major keystone in the development of the Moderna and Pfizer vaccines now being used to help fight the coronavirus pandemic.

He was also invited to lecture internationally, collaborated with colleagues from around the world, and edited several scientific journals.

But throughout his life, nature was Mr. Welsh’s great inspiration.

“It was such a passion,” said his wife, Barbara.

Particularly important to him was Yosemite National Park, which he first visited as an undergraduate student at Stanford University. It was through Yosemite that Mr. Welsh got to develop a feeling of great kinship with the late John Muir, the famed Scottish naturalist and conservationist who also loved Yosemite. Throughout Mr. Welsh’s adult life, he visited the park almost yearly, sometimes more than once year, and into his 70s.

“It was like his spiritual home,” his wife said. “There was always something about Yosemite that touched him to the core.”

In June 2018, the couple made what would be one of his last trips to Yosemite, that time with their grandchildren in tow.

“We were introducing our very young grandchildren to the park for the first time,” Barbara Welsh said. “That was so important to him.”

The mountains and canyons of Yosemite were a far cry from Evanston, Ill., where Mr. Welsh was born, and Rockford, Ill., where he was raised playing golf and rooting for the then-Milwaukee Braves. After he left to earn a bachelor of science degree in chemistry, he went on to get his doctorate in pharmacology from Washington University in St. Louis and was a postdoctoral fellow in biochemistry at Duke University.

But his love of baseball stuck.

From 1981 to when his legs ceased to cooperate, he played with friends on the local Sunday Morning Baseball group, usually second or third base. He coached Little League in St. Louis, Chapel Hill, N.C., and Radnor. Since boyhood, he also played a board baseball game called APBA and, in retirement, joined a local group of players, becoming the group’s commissioner. His team name was the same as the one used by the late City Councilman Thacher Longstreth when he played APBA — The Argyle Socks.

Mr. Welsh also sought out opportunities to work with children and youth. He had served as a leader in local Webelos and Boy Scout groups. He advised high school youth at the Main Line Unitarian Church, where he was a member. In addition, he was a leader in a local Sierra Club program that helps city youth from Philadelphia explore nearby parklands.

A man of science and a gentle lover of the earth, Mr. Welsh was loved and admired by many different people, according to John F. Smith, board chair emeritus of the nonprofit Global Philadelphia Association.

“How do you measure the value of a life like Dusty’s?” asked Smith. “He was a groundbreaking scientific researcher, a devoted lover of nature, an adviser to youth, a leader by example. But in a world where self-promotion often reigns, he never talked about his many accomplishments, preferring to let them speak for themselves instead. Most importantly, he was our friend. We loved him and yearned to be like him.”

In addition to his wife of 54 years, Mr. Welsh is survived by sons Edward and Frank Alexander IV, four grandchildren, and other relatives.

A Celebration of Life is being planned for a future date.

In lieu of flowers, family and friends are invited to contribute to the nature group of their choice.