The term ‘pedigree collapse’ was coined by Robert Gunderson of the Genealogical Society of Utah. Essentially, it refers to a reduction in the number of ancestors a person has due to the relationship of their parents. For example, if two first cousins marry and reproduce, their child will have, at most, six great-grandparents rather than the usual eight. Without pedigree collapse a person’s ancestral tree would become impossibly large – going back to the Middle Ages my family tree woul...