Ruth Ashdown
Ruth is a family historian with an actuary's fondness for tables. She writes the genealogy mathematics: cousins and removes, relatedness, pedigree collapse and how many years a generation really is.
Explainers by Ruth
Teaching kinship with a spreadsheet, one row per person
Build a small genealogy in Excel or Google Sheets: one row per person, formulas that find grandparents, siblings and cousins, and a lookup that names relatives.
Pedigree collapse: why no one has a billion ancestors
Why the doubling of ancestors cannot go on: pedigree collapse worked through with small numbers, the Spanish Habsburgs, and what Chang and Rohde found.
The coefficient of relationship, worked out by hand
Sewall Wright's path method for the coefficient of relationship, worked step by step for siblings, uncles, cousins and double cousins, with what DNA adds.