eg:
Some sociologists and anthropologists consider the extended family structure to be the most common family structure in most cultures and at most times for humans, rather than the nuclear family.
~ https://en.wikipedia.org/wiki/Nuclear_familywhich also provides the common use definitions:
A nuclear family (also known as an elementary family, atomic family, or conjugal family) is a term for a family group consisting of parents and their children (one or more), typically living in one home residence.
It is in contrast to a single-parent family, a larger extended family, or a family with more than two parents.
Other sources include: Families Across Cultures: A 30-Nation Psychological Study (2006) from Cambridge press by the same author cited in wikipedia (James Georgas) and others: John W. Berry, Fons J. R. van de Vijver, Cigdem Kagitcibasi, Ype H. Poortinga Contemporary trends such as increased one-parent families, high divorce rates, second marriages and homosexual partnerships have all contributed to variations in the traditional family structure.
But to what degree has the function of the family changed and how have these changes affected family roles in cultures throughout the world? This book attempts to answer these questions through a psychological study of families in thirty nations, carefully selected to present a diverse cultural mix.
The study utilises both cross-cultural and indigenous perspectives to analyse variables including family networks, family roles, emotional bonds, personality traits, self-construal, and 'family portraits' in which the authors address common core themes of the family as they apply to their native countries.
From the introductory history of the study of the family to the concluding indigenous psychological analysis of the family, this book is a source for students and researchers in psychology, sociology and anthropology.