A pedigree shows the members of a kindred. The kindred consists of one’s immediate family and other relatives, including uncles and aunts, cousins, great uncles and great aunts. Those who do genealogy know how fast such pedigrees can grow. In human genetics they are useful for identifying relatives at risk for inherited disorders and genetic counselors frequently take such extended family histories when figuring out the passage of genes to an affected child. I have frequently prepared such pedigrees for students when they ask me about a genetic condition running in their families. The geneticist uses circles to represent females and squares to represent males. They are connected by horizontal and vertical lines to show their relationship to one another.
Scholars sometimes construct a different kind of pedigree. They like to show how they are connected to other scholars. This is almost as much fun as learning who one’s ancestors were. For example, I got my PhD at Indiana University with Nobelist H. J. Muller who first induced mutations with x-rays in 1927. He got his PhD with T. H. Morgan who got his Nobel Prize in 1933 for working out the principles of classical genetics with fruit flies, chiefly for his work on what is called X-linked inheritance (traits such as color blindness, hemophilia, and Duchenne muscular dystrophy) and crossing over (the shuffling of genes between related chromosomes). Morgan was at Columbia University when this work was done by his laboratory. Morgan got his PhD with William Keith Brooks and H. Newell Martin at Johns Hopkins University, the first modern graduate research program in the United States. Brooks was a zoologist who studied oysters and other invertebrates. Martin was from England, recruited because he was an experimental physiologist. Brooks got his PhD from Alexander Agassiz at Harvard. Agassiz was a founder of Woods Hole, the first experimental biology station in the US. Martin got his advanced training from Thomas Henry Huxley, an evolutionist who was influenced by Charles Darwin and who championed his work for him. He was so effective speaking in public on behalf of Darwin’s views on evolution that he is known as “Darwin’s Bulldog.” Alexander Agassiz got his graduate education from his father, Louis Agassiz, one of America’s most famous nineteenth century scientists who came to the US from Switzerland. He was the Carl Sagan of his day and did much to popularize science in America.
In a genetic pedigree there is a reduction by 50% of the amount of heredity one gets from each ancestor as one moves back one generation. Thus my great-great grandfather, Carl Frederick Pettersson, contributed about 7% of my genes. There is no way to assess the influence of ideas in one’s intellectual pedigree. Most of the intellectual heirs of Darwin shared an enthusiasm for evolution by natural selection. But none of the intellectual heirs of Louis Agassiz shared his views on the Divine Creation of life. Agassiz, true intellect that he was, respected his own students who all became strong supporters of Darwin’s theory of evolution by natural selection. While heredity distributes its genes across the generations in predictable ways, ideas are far more uncertain. Some ideas are shared indefinitely after they are established and others may be short-lived.