A half-century ago, when researchers said cancers were caused by exposure to toxins in the environment, Dr. Henry T. Lynch begged to differ.

Many cancers, he said, were hereditary. To prove his point he traveled to gatherings of families that he suspected had histories of hereditary cancer. He arranged to meet family members and asked: Who in the family had cancer? What kind of cancer? Could he get medical records, and blood samples, which he could freeze and store?

He hand-drew family trees, with squares for men and circles for women, marking who got cancer and what kind. He was soon insisting to a doubting world that he had found compelling evidence of genetic links.

In time, the medical world accepted his claims, and his work — the family trees, the blood samples — eventually contributed to the discovery, by others, of a gene that when mutated can lead to colon cancer and an array of other cancers. He also contributed work that led to the discovery of gene mutations that greatly increase the risk of breast and ovarian cancer.